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Assembling molecular triangles into discrete and infinite architectures
Abstract
Having established that molecules with general formulae [MnIII6O2(R-sao)6(O2CR)2(L)4–6] ([Mn6]) and [MnIII3O(R-sao)3(X)(L)3] ([Mn3]) (saoH2 = salicylaldoxime; R = H, Me, Et etc; X = RCO2−, ClO4−; L = solvent), with the latter being the analogous “half” molecules of the former, exhibit the phenomenon of single-molecule magnetism, we have exploited them as building blocks to construct supramolecular architectures by means of host–guest interactions and coordination driven self-assembly. A number of discrete and infinite architectures, namely [MnIII3O(Ph-sao)3(4Cl-sbz)3(MeOH)3]2(OH)(ClO4)·2MeOH (1·2MeOH), [MnIII3O(Ph-sao)3(4Me-sbz)3(EtOH)3]2(OH)(NO3) (2), {[MnIII3O(Et-sao)3(4,4′-bpy)2(MeOH)] ClO4·1.5MeOH·Et2O}n (3·1.5MeOH·Et2O), {[MnIII3O(sao)3(4,4′-bpe)1.5]ClO4·3MeOH}n (4·3MeOH) and [{MnIII3O(Et-sao)3(O2CPh)(EtOH)}2{4,4′-bpe}2] (5), based on the molecular triangle [Mn3] and various pyridyl-type ligands (4Cl-sbz = 4-chlorostilbazole, 4Me-sbz = 4-methylstilbazole, 4,4′-bpy = 4,4′-bipyridine and 4,4′-bpe = trans-1,2-bis(4-pyridyl)ethylene) were obtained and structurally and magnetically characterized.
... The two most studied families of oxime groups in Molecular Magnetism are the salicyl aldo(keto)ximes and the 2-pyridyl aldo(keto)ximes, Figure 21. The former [142][143][144][145][146][147][148][149][150][151][152][153][154][155] have led to a variety of clusters with exciting molecular structures and magnetic properties; they have been used, among others, in the development of a synthetic process widely known as "ground-state spin switching and enhancing SMM properties via targeted structural distortion" strategy [56,[142][143][144][145][147][148][149]. The latter [156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171][172][173][174], in addition to their involvement in the synthesis of 3d-metal SIMs [158], have provided access to interesting 3d-metal clusters and SMMs. ...
... Excluding utilization of hydrogen bonds, with which it is difficult to control oligomerization and to achieve retention of the supramolecular structure in solution, the best solution is the designed linking of SMMs via coordination bonds. The groups of Papaefstathiou, Escuer, Brechin and Christou [150][151][152][153][170][171][172][173][174], among others, have used building-block strategies to link SMMs together employing carefully chosen linkers that provide inter-SMM interactions and ensure the formation of discrete oligomeric (and not polymeric) species. ...
There has been a renaissance in the interdisciplinary field of Molecular Magnetism since ~2000, due to the discovery of the impressive properties and potential applications of d- and f-metal Single-Molecule Magnets (SMMs) and Single-Ion Magnets (SIMs) or Monometallic Single-Molecule Magnets. One of the consequences of this discovery has been an explosive growth in synthetic molecular inorganic and organometallic chemistry. In SMM and SIM chemistry, inorganic and organic ligands play a decisive role, sometimes equally important to that of the magnetic metal ion(s). In SMM chemistry, bridging ligands that propagate strong ferromagnetic exchange interactions between the metal ions resulting in large spin ground states, well isolated from excited states, are preferable; however, antiferromagnetic coupling can also lead to SMM behavior. In SIM chemistry, ligands that create a strong axial crystal field are highly desirable for metal ions with oblate electron density, e.g., TbIII and DyIII, whereas equatorial crystal fields lead to SMM behavior in complexes based on metal ions with prolate electron density, e.g., ErIII. In this review, we have attempted to highlight the use of few, efficient ligands in the chemistry of transition-metal SMMs and SIMs, through selected examples. The content of the review is purely chemical and it is assumed that the reader has a good knowledge of synthetic, structural and physical inorganic chemistry, as well as of the properties of SIMs and SMMs and the techniques of their study. The ligands that will be discussed are the azide ion, the cyanido group, the tris(trimethylsilyl)methanide, the cyclopentanienido group, soft (based on the Hard-Soft Acid-Base model) ligands, metallacrowns combined with click chemistry, deprotonated aliphatic diols, and the family of 2-pyridyl ketoximes, including some of its elaborate derivatives. The rationale behind the selection of the ligands will be emphasized.
... A good strategy is the use of building-block approaches to link SMMs together employing carefully chosen linker groups that will provide weak inter-SMM interactions and ensure that discrete oligomeric species (and not polymers) are obtained. The groups of Papaefstathiou, Brechin, Christou, and Escuer, among others, have successfully contributed into this general synthetic goal Inglis et al., 2010;Cordero et al., 2011;Nguyen et al., 2011Nguyen et al., , 2015Nguyen et al., , 2016Mowson et al., 2013). We herein present examples of the supramolecular approaches which have been almost exclusively developed in Mn SMM chemistry. ...
The area of 3d-metal coordination clusters that behave as Single-Molecule Magnets (SMMs) is now quite mature within the interdisciplinary field of Molecular Magnetism. This area has created a renaissance in Inorganic Chemistry. From the synthetic Inorganic Chemistry viewpoint, the early years of “try and see” exercises (1993–2000) have been followed by the development of strategies and strict approaches. Our review will first summarize the early synthetic efforts and routes for the preparation of polynuclear 3d-metal SMMs, and it will be then concentrated on the description of the existing strategies. The former involve the combination of appropriate 3d-metal-containing starting materials (simple salts with inorganic anions, metal cardoxylates, and pre-formed carboxylate clusters, metal phosphonates) and one or two primary organic ligands; the importance of the end-on azido group as a ferromagnetic coupler in 3d-metal SMM chemistry will be discussed. The utility of comproportionation reactions and the reductive aggregation route for the construction of manganese SMMs will also be described. Most of the existing strategies for the synthesis of SMMs concern manganese. These involve substitution of carboxylate ligands in pre-formed SMMs by other carboxylate or non-carboxylate groups, reduction procedures for the {Mn8IIIMn4IV} SMMs, spin “tweaking,” “switching on” SMM properties upon conversion of low-spin clusters into high-spin ones, ground-state spin switching and enhancing SMM properties via targeted structural distortions, the use of radical bridging ligands and supramolecular approaches. A very useful strategy is also the “switching on” of SMM behavior through replacement of bridging hydroxide groups by end-on azido or isocyanato ligands in clusters. Selected examples will be mentioned and critically discussed. Particular emphasis will be given on the criteria for the choice of ligands.
This chapter provides information on the most often used synthetic methods for the preparation of homometallic and heterometallic single‐molecule magnets. It explains the most appropriate synthetic methods for the preparation of single‐ion magnets (SIMs). The chapter covers the main synthetic routes and methods for the isolation of single‐molecule magnets (SMMs) and SIMs. It discusses the synthetic aspects for polynuclear 3d metal SMMs and dinuclear and polynuclear 4f metal complexes with SMM properties and actinide SMMs. After a brief introduction about the specific type of SMMs/SIMs, it presents a short discussion concerning the criteria for the selection of the metal ion(s) and the choice of the ligands (both inorganic and organic ligands) used. The structures and magnetic properties of the resulting SMMs and SIMs are briefly mentioned. The emphasis is on the chemistry and the rationale that are behind this. Finally, the chapter provides some concluding comments and gives the authors' prognosis for the future.
Employment of di-2-pyridyl ketone and poly-carboxylates in the CuII chemistry has afforded four complex hydrogen-bonded frameworks, one 1D, one 2D and three 3D coordination polymers. Di-2-pyridyl ketone has undergone several metal-assisted transformations to yield three CuII structural units which in combination with the poly-carboxylate anions of the trimesic, isophthalic, 5-hydroxy-isophthalic and pyromellitic acids provided access to extended frameworks by either dative or hydrogen bonds. All nine complex frameworks were realized in terms of their topological analysis. The 3D and the 2D polymers consist of [Cu2] dimers and found to be dominated by ferromagnetic interactions. The origin of the ferromagnetic coupling was attributed to the counter complementarity of the simultaneous alkoxo / syn,syn-carboxylate bridges within the dimers.
The reaction of MnCl2·4H2O with salicylaldoxime (H2salox) and the sodium salt of 1,3-bis(carboxypropyl)tetramethyldisiloxane (H2L) in a 1:1:1 molar ratio led to the self-assembly of {[Mn6O2(salox)6(H2salox)(H2O)3(μ-L)]H2salox·1.2H2O}n, a 1D coordination polymer consisting of hexamanganese(III) salicylaldoximate cluster as secondary building unit (SBU) and tetramethyldisiloxane-based dicarboxylate linker, namely, 1,3-bis(carboxypropyl)tetramethyldisiloxane. The structure of the compound was established by single crystal X-ray diffraction. The Mn(III) clusters consist of two staggered μ3-oxo-bridged Mn3 triangles held together by the oxygen atoms of the oxime groups. Because of Jahn–Teller distortion, the Mn–O distances reach 2.5 Å for the oxygen atoms located above and below the triangles mean planes. The compound showed a glass transition peak at around 14 °C in the differential scanning calorimetry (DSC) curve. The magnetic susceptibility data were fitted with a set of three intracluster antiferromagnetic exchange interaction coupling constants: J1 = −0.65 cm–1, J2 = −1.5 cm–1, and J3 = −0.9 cm–1. The ac magnetic susceptibility measurements in the 2–5 K temperature range reveal a frequency-dependent behavior indicative of a slow relaxation of magnetization at low temperature. The coexistence of the lypophilic 1,3-bis(propyl)tetramethyldisiloxane moieties and hydrophilic polar SBUs confers to the structure an amphiphilic character. Dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and transmission (TEM) and scanning (SEM) electron microscopies demonstrate that in dimethylformamide (DMF) the coordination polymer organizes as micelles, whereas in chloroform it tends to form inverse micelles and vesicles.
Quantum coherence and entanglement give resources to enhance the capabilities of computers well beyond those achievable by present-day or even future classical devices. Quantum information processing can be carried out via a combination of two elementary logic operations: unitary rotations of individual qubits and quantum-gate operations that involve at least two coupled qubits. An outstanding challenge for science and technology is to find suitable realizations of these basic elements. In recent years, magnetic molecular clusters have become candidates to implement the quantum computer hardware. Here, we summarize some of the strategies that have been followed to design and synthesize molecular spin qubits and quantum gates. In particular, we show that molecular clusters containing two Tb3+ ions meet all ingredients required to implement a CNOT quantum logic gate. The definition of control and target qubits is based on the strong magnetic anisotropy and the magnetic inequivalence of the two ions, which can be achieved by chemically engineering dissimilar coordination spheres. The magnetic asymmetry also provides a method to realize a SWAP gate in the same cluster. The synthesis of related molecular structures enables a vast choice of quantum-gate designs. Chemically engineered molecular quantum gates can therefore open promising avenues for the realization of scalable quantum computing architectures.
The syntheses and properties of four magnetically-supramolecular oligomers of triangular Mn3 units are reported: dimeric [Mn6O2(O2CMe)8(CH3OH)2(pdpd)2] (3) and [Mn6O2(O2CMe)8(py)2(pdpd)2](ClO4)2 (4), and tetrameric [Mn12O4(O2CR)12(pdpd)6](ClO4)4 (R = Me (5),
t
Bu (6)). They were all obtained employing 3-phenyl-1,5-di(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH2), either in direct synthesis reactions involving oxidation of MnII salts or in metathesis reactions with the preformed complex [Mn3O(O2CMe)6(py)3](ClO4) (1); complex 6 was then obtained by carboxylate substitution on complex 5. Complexes 3 and 4 contain two [MnIII2MnII(μ3-O)]6+ and [MnIII3(μ3-O)]7+ units, respectively, linked by two pdpd2- groups. Complexes 5 and 6 contain four [MnIII3(μ3-O)]7+ units linked by six pdpd2- groups into a rectangular tetramer [MnIII3]4. Solid-state dc magnetic susceptibility studies showed that the Mn3 subunits in 3 and 4 have a ground-state spin of S = 3/2 and S = 2, respectively, while the Mn3 subunits in 5 and 6 possess an S = 6 ground state. Complexes 5 and 6 exhibit frequency-dependent out-of-phase (χ''M) ac susceptibility signals indicating 5 and 6 to be tetramers of Mn3 single-molecule magnets (SMMs). High-frequency EPR studies of a microcrystalline powder sample of 5·2CH2Cl2 provided precise spin Hamiltonian parameters of D = -0.33 cm-1, |E| = 0.03 cm-1, B04 = -8.0 × 10-5 cm-1, and
g
= 2.0. Magnetization vs. dc field sweeps on a single crystal of 5·xCH2Cl2 gave hysteresis loops below 1 K that exhibit exchange-biased quantum tunneling of magnetization (QTM) steps with a bias field of 0.19 T. Simulation of the loops determined that each Mn3 unit is exchange-coupled to the two neighbors linked to it by the pdpd2- linkers, with an antiferromagnetic inter-Mn3 exchange interaction of J/kB = -0.011 K (Ĥ = -2Jŝ
i
·ŝ
j
convention). The work demonstrates a rational approach to synthesizing magnetically-supramolecular aggregates of SMMs as potential multi-qubit systems for quantum computing.
In this account, we discuss some metal–organic frameworks (MOFs) that are based on single‐molecule magnets (SMMs). Although the fields of MOFs and SMMs have independently grown rapidly over the last two decades, examples of SMM‐based MOFs are limited, with those possessing a 3D framework numbering just a handful. MOFs are robust porous molecular materials that are predominantly based on polynuclear metal complexes (clusters) owing their properties to their open framework structures. SMMs, on the other hand, are interesting in their own right as they constitute a very special kind of polynuclear metal complex, having the ability to store magnetic information at the molecular level. Although the properties of SMMs are of molecular origin, they can be influenced by crystal‐packing effects, especially at low temperatures. As expected, the combination of these two molecular materials benefits both fields, as SMMs can carry their magnetic properties to a MOF, while their incorporation within a framework may alter/modulate their magnetic properties. Therefore, a new class of molecular materials rises from the combination of the two. Although this new field is very much in its infancy, early examples of SMM‐based MOFs promise much exciting chemistry (and physics) for both academic intuition and an applications‐driven perspective. We hope that this account will inspire scientists to make many more such SMM‐based MOFs and study their properties.
Phenolic oximes, which are frequently used as bridging ligands in the construction of molecule-based magnets, have stimulated considerable interest in magnetochemistry. This tutorial review is concentrated on manganese-based phenolic oximes systems and related magnetochemistry and consists of five main sections. The first section offers an introduction to Mn-based phenolic oxime complexes and some important results obtained from magneto–structural correlations in phenolic oximes compounds which will be discussed in the following sections. The next three sections provide overviews of phenolic oximes-mediated Mn compounds from zero-dimension to one-, two- and three-dimensional supramolecular architectures and their unusual magnetic properties including SMM and SCM behavior. The last section contains concluding remarks and provides perspectives for the future of phenolic oximes-mediated compounds.
In an attempt to employ salicylic acid (HOsalH), 2,6-dihydroxy benzoic acid {(HO)2PhCO2H} and naphthalene-1,8-dicarboxylic acid {1,8-naph(CO2H)2} in Mn(III) salicylaldoximate chemistry as a means to alter the structural identity of the hexanucluear clusters usually obtained from this reaction system, we have isolated a family of hexanuclear Mn(III) complexes based on salicyladloxime (saoH2) and 2-hydroxy-1-naphthaldehyde oxime (naphthsaoH2). Five hexanuclear clusters of formulae [Mn6O2(sao)6(HOsal)2(EtOH)4]•EtOH (1•EtOH), [Mn6O2(sao)6{1,8-naph(CO2Me)(CO2)}2(MeOH)6]•3MeOH (2•3MeOH), [Mn6O2(naphthsao)6{1,8-naph(CO2Et)(CO2)}2(EtOH)6] (3•2MeOH), [Mn6O2(naphthsao)6(MeCO2)2(EtOH)4]•2H2O (4•2H2O) and [Mn6O2(naphthsao)6{(HO)2PhCO2}2(EtOH)4]•4EtOH (5•4EtOH) have been synthesized and characterized by single-crystal x-ray crystallography. The magnetic properties of complexes 3, 4 and 5 are discussed.
Controlled organization of high-spin complexes and single-molecule magnets is a great challenge in molecular magnetism in order to study the effect of the intercomplex magnetic interactions on the intrinsic properties of a given magnetic object. In this work, a new ST = 7 trinuclear mixed-valence Mn complex, [Mn(III)Mn(II)2(LA)2(Br)4(CH3OH)6] ·Br·(CH3OH)1.5·(H2O)0.5 (1), is reported using a pyridinium-functionalized 1,3-propanediol ligand (H2LABr = 1-(3-bromo-2,2-bis(hydroxymethyl)propyl)pyridinium bromide). Using azido anions as bridging ligands and different pyridinium-functionalized 1,3-propanediol ligands (H2LBBr = 1-(3-bromo-2,2-bis(hydroxymethyl)propyl)-4-picolinium bromide; H2LCBr = 1-(3-bromo-2,2-bis(hydroxymethyl)propyl)-3,5-lutidinium bromide), the linear [Mn(III)Mn(II)2L2X4](+) building block has been assembled into one-dimensional coordination networks: [Mn(III)Mn(II)2(LA)2(Br)4(CH3OH)4(N3)]·((C2H5)2O)1.25 (2∞), [Mn(III)Mn(II)2(LB)2(Br)4(C2H5OH)(CH3OH)(H2O)2(N3)]·(H2O)0.25 (3∞), and [Mn(III)Mn(II)2(LC)2(Cl)3.8(Br)0.2(C2H5OH)3(CH3OH)(N3)] (4∞). The syntheses, characterization, crystal structures, and magnetic properties of these new [Mn3]-based materials are reported.
Three new coordination polymers [Mn4(bptca)2(titmb)(H2O)7]·DMF·4H2O (1), [Ni2(bptca)(titmb)2]·13H2O (2) and [Co2(bptca)(titmb)2]·13H2O (3) were constructed from 4,4′-bipyridine-2,2′,6,6′-tetracarboxylic acid (H4bptca) and 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb) under hydrothermal conditions. Single crystal X-ray diffraction analysis shows that 1 contains [Mn4(μ2-OCO)4] subunits linked through organic ligands to form a two-dimensional (2D) double-layer structure, while 2 and 3 are isostructural and exhibit a unique three-dimensional (3D) framework with open channels resided by water molecules. The magnetic behavior of 1 and sorption property of 2 have been investigated.
A monomolecular four center low spin paramagnetic organometallic
complex is proposed and theoretically studied to work as a controlled quantum
swap molecule logic gate. The magnetic super-exchange interaction between the 2
intramolecular qubits depends on the oxydation state of a third intermediate center
itself controlled by an intervalence electron transfer process. A model system is
build up using entangled spin qubits in the framework of an Heisenberg-Dirac-Van
Vleck like spin Hamiltonian demonstrating the effective swapping operation of this
complex.
A mixed-valent [Mn12] complex with an unprecedented [MnIII4MnII8(μ-OCH3)4] core was obtained by oxidation of MnCl2 in the presence of salicylaldoxime (saoH2). This complex adopts a rare topology based on a central [MnII4] cage decorated by four dinuclear [MnII–MnIII] motifs. Studies of the magnetic properties show the presence of strong intracomplex antiferromagnetic interactions and suggest an ST = 2 spin ground state.
A triangular Mn(III) complex with an [Mn III3μ3- O(sao) 3] unit (sao - doubly deprotonated salicylaldoxime) and unprecedented coordination by a TPO (triphenylphosphine oxide) ligand is the result of a transfer of the TPO ligand from a rhenium(V) complex onto a preformed [Mn III3O] unit. In the crystal structure, isomeric complex molecules with different patterns of their terminal substituents form hydrogen-bonded dimers.
Two Mn(4) single-molecule-magnet (SMM)-based coordination polymers, {[Mn(4)O(salox)(3)(N(3))(3)(DMF)(2)(H(2)O)(dpp)]·0.5MeOH}(n) (1·0.5MeOH; H(2)salox = salicylaldoxime; dpp = 1,3-di-4-pyridylpropane; DMF = N,N-dimethylformamide) and {[Mn(4)O(Me-salox)(3)(N(3))(3)(dpp)(1.5)]·1.5Et(2)O}(n) (2·1.5Et(2)O; Me-H(2)salox = hydroxyphenylethanone oxime), are self-assembled from Mn(ClO(4))(2)·6H(2)O/H(2)salox and Mn(ClO(4))(2)·6H(2)O/Me-H(2)salox systems with dpp and NaN(3) in DMF/MeOH, respectively. Both compounds comprise a mixed-valence tetranuclear manganese core, [Mn(II)Mn(III)(3)O](9+), which serves as a building unit for subsequent assembly via oximate and azido ligands. The flexible dpp ligand links with a Mn(4) unit, leading to the formation of a one-dimensional helical structure in 1·0.5MeOH and a three-dimensional pcu network in 2·1.5Et(2)O. The magnetic data analysis shows that antiferromagnetic interactions within the Mn(4) units resulted in S = (3)/(2) and (7)/(2) ground states for 1·0.5MeOH and 2·1.5Et(2)O, respectively. Both compounds show SMM behavior, as evidenced by frequency-dependent out-of-phase signals in alternating-current magnetic susceptibility and magnetic hysteresis loop studies with an energy barrier of U(eff) = 37 K for 2·1.5Et(2)O.
The reaction of Mn(HCOO)(2)·2H(2)O, (t)BuSaoH(2) (3,5-di-tert-butyl-salicylaldoxime) and sodium azide in isopropanol leads to [NaMn(3)((t)BuSao)(6)] (1). Its structure can be described as a linear trinuclear cluster bridged by oximato ligands. Magnetic investigation revealed that the ferromagnetic coupling interaction is dominant in 1 leading to a ground-state spin S(T) = 5. 1 shows single-molecule magnet behaviour under zero or 1 kOe dc field with energy barrier U(eff)∼ 10 K.
The field of molecular magnetism has rapidly expanded since the discovery of single-molecule magnets (SMMs) at the beginning of the 1990s. Numerous SMMs have been studied and a broad community currently works on these systems to improve their magnetic characteristics. However, it has also become an important strategy to diversify a part of our research activity toward the organization of these magnetic molecules in order to move closer to future applications. One of the possible ways is to utilize SMMs as molecular building blocks and assemble them with the help of coordination chemistry. This strategy presents a significant challenge since the intrinsic magnetic properties of the parent SMMs can be modified, which consequently also provides a unique opportunity to investigate new behaviours at the frontier between SMMs and classical bulk magnets. Furthermore, the design of systems with "enhanced" SMM properties or magnet behaviour is theoretically possible by choosing coordinating linkers that could favour an effective ferromagnetic arrangement of the SMMs. In this perspective article, we will give an overview of the known networks based on SMMs with an emphasis on the synthetic strategies, magnetic properties, and finally possible routes to a new generation of molecular magnetic materials.
The dimeric complex [Mn(III)(2)(Naphth-sao)(2)(Naphth-saoH)(2)(MeOH)(2)]·4MeOH (1·4MeOH), acts as a simple model complex with which to examine the magneto-structural relationship in polymetallic, oxime-bridged Mn(III) complexes. Dc magnetic susceptibility studies reveal that ferromagnetic exchange is mediated through the heavily twisted Mn-O-N-Mn moiety (J = +1.24 cm(-1)) with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high field, high frequency EPR data reveal a single ion anisotropy, D((Mn(III))) = -3.94 cm(-1). Theoretical studies on simplified model complexes of 1 reveal that calculated values of the exchange coupling and the anisotropy are in excellent agreement with experiment, with the weak ferromagnetism resulting from an accidental orthogonality between the Mn-N-O plane of the first Mn(III) ion and the Jahn-Teller axis of the second Mn(III) ion.
The use of derivatised salicylaldoximes in manganese chemistry has led to the synthesis of a family of approximately fifty hexanuclear ([Mn(III)(6)]) and thirty trinuclear ([Mn(III)(3)]) Single-Molecule Magnets (SMMs). Deliberate, targeted structural distortion of the metallic core afforded family members with increasingly puckered configurations, leading to a switch in the pairwise magnetic exchange from antiferromagnetic to ferromagnetic. Examination of both the structural and magnetic data revealed a semi-quantitative magneto-structural correlation, from which the factors governing the magnetic properties could be extracted and used for predicting the properties of new family members and even more complicated structures containing analogous building blocks. Herein we describe an overview of this extensive body of work and discuss its potential impact on similar systems.
The serendipitous self-assembly of the complex [Mn(III)(2)Zn(II)(2)(Ph-sao)(2)(Ph-saoH)(4)(hmp)(2)] (1),whose magnetic core consists solely of two symmetry equivalent Mn(iii) ions linked by two symmetry equivalent -N-O- moieties, provides a relatively simple model complex with which to study the magneto-structural relationship in oxime-bridged Mn(III) cluster compounds. Dc magnetic susceptibility measurements reveal ferromagnetic (J = +2.2 cm(-1)) exchange resulting in an S = 4 ground state. Magnetisation measurements performed at low temperatures and high fields reveal the presence of significant anisotropy, with ac measurements confirming slow relaxation of the magnetisation and Single-Molecule Magnetism behaviour. Simulations of high field, high frequency EPR data reveal a single ion anisotropy, D((Mn(III))) = -3.83 cm(-1). DFT studies on a simplified model complex of 1 reveal a pronounced dependence of the exchange coupling on the relative twisting of the oxime moiety with respect to the metal ion positions, as suggested previously in more complicated [Mn(III)(3)] and [Mn(III)(6)] clusters.
The exploration of the NiX(2)/py(2)CO/Et(3)N (X = F, Cl, Br, I; py(2)CO = di-2-pyridyl ketone; Et(3)N = triethylamine) reaction system led to the tetranuclear [Ni(4)Cl(2){py(2)C(OH)O}(2){py(2)C(OMe)O}(2)(MeOH)(2)]Cl(2)·2Et(2)O (1·2Et(2)O) and [Ni(4)Br(2){py(2)C(OH)O}(2){py(2)C(OMe)O}(2)(MeOH)(2)]Br(2)·2Et(2)O (2·2Et(2)O) and the trinuclear [Ni(3){py(2)C(OMe)O}(4)]I(2)·2.5MeOH (3·2.6MeOH), [Ni(3){py(2)C(OMe)O}(4)](NO(3))(0.65)I(1.35)·2MeOH (4·2MeOH) and [Ni(3){py(2)C(OMe)O}(4)](SiF(6))(0.8)F(0.4)·3.5MeOH (5·3.5MeOH) aggregates. The presence of the intermediate size Cl(-) and Br(-) anions resulted in planar tetranuclear complexes with a dense hexagonal packing of cations and donor atoms (tetramolybdate topology) where the X(-) anions participate in the core acting as bridging ligands. The F(-) and I(-) anions do not favour the above arrangement resulting in triangular complexes with an isosceles topology. The magnetic properties of 1-3 have been studied by variable-temperature dc, variable-temperature and variable-field ac magnetic susceptibility techniques and magnetization measurements. All complexes are high-spin with ground states S = 4 for 1 and 2 and S = 3 for 3.
Recent examples of interpenetrating and self-penetrating networks are highlighted in a discussion of interpenetration topology. A web site (http://web.chem.monash.edu.au/Department/Staff/Batten/Intptn.htm) has been set up which contains a tabulated list of all known examples of interpenetration.
The articles published in the tenth anniversary issue of CrystEngComm are reviewed. The issue highlighted the state-of-the-art of crystal engineering and new trends and developing areas in crystal engineering. In particular, the following article emphasises developments in the areas of intermolecular interactions, notably hydrogen and halogen bonds; metal–organic frameworks or coordination polymers; polymorphism and solvates.
We report three heptanuclear [Ni 7 ] complexes with planar disc-like cores, akin to double-bowl metallocalix[6]arenes, which form molecular H-bonded host cavities. Polymetallic complexes of paramagnetic 1st row transition metal ions are of great current interest since they often exhibit fascinating physical properties such as spin-crossover behaviour, 1 long range ordering (i.e. in 1-, 2-and 3D coordination polymers 2) and single-molecule magnet (SMM) behaviour. 3 Ni II in particular, has shown much promise in the synthesis of both single-molecule magnets (SMMs) and spin phonon traps; the former taking advantage of its significant single-ion anisotropy and the latter its paramagnetic nature when confined within a highly symmetric cage. 4–6 In addition, the use of magnetic clusters as building blocks to create supramo-lecular architectures (i.e. discrete polyhedra 7 and 1-, 2-and 3D polymers 8) using both covalent and non-covalent interactions has led to materials whose physical properties can be rather different to that of their parent paramagnetic building blocks. 9 An important factor in the construction of such assemblies is the choice of ligand, since this dictates not only cluster symmetry, topology and the number of paramagnetic metal ions present, but also the inter-molecular interactions between clusters in the crystal. Our own interest in this area has recently led us to investigate the coordination chemistry of the Schiff-base ligand 2-iminomethyl-6-methoxy-phenol (HL 1) and its bromo-analogue 2-iminomethyl-4-bromo-6-methoxy-phenol (HL 2) (Fig. 1) and herein report its initial coordination and supramolecular chemistry with Ni II . Reaction of Ni(NO 3) 2 $6H 2 O and HL 1 in the presence of NaOH in EtOH produces the heptanuclear complex [Ni 7 (m 3 -OH) 6 (L 1) 6 ](NO 3) 2 (1) in 30% yield. The green hexagon shaped crystals of 1 crystallize in the trigonal space group P-3c1 (Fig. 1). Heptanuclear complex 1 possesses a core comprising a hexagon of Ni II ions surrounding a central Ni II centre. The central Ni II ion (Ni1) is located at a site with imposed 3 symmetry while the nitrogen atom (N2) of the NO 3 À group lies on a threefold axis. The remainder of the asymmetric unit comprises a second Ni II centre (Ni2) along with one L 1 À unit and one hydroxy group (O1–H1) occupying general positions. Although topologically analogous [Mn 7 ], 10 [Fe 7 ] 11 and [Co 7 ] 12 complexes are known, the synthesis of 1 represents the first nickel complex to possess a planar hexagonal disc-like structure. All Ni ions are in distorted octahedral geometries with the six m 3 -bridging OH À ions (O1) linking the central nickel (Ni1) to the six peripheral nickel ions (Ni2); each trigonal pyramidal OH À ion being situated alternately above and below the [Ni 7 ] plane (Fig. 1). The anionic ligands L 1 À (singly deprotonated at the phenolate site) bridge the peripheral Ni II centres adopting a m 2 -h 1 :h 2 :h 1 coordination motif, lying alternately above and below the [Ni 7 ] plane. The result is a double-bowl conformation in which the [Ni 7 ] core is the basal plane, reminiscent of a metallocalix[6]arene concave unit (Fig. 1). Close inspection of the double-bowl conformation shows approximate bowl dimensions of (base  depth  rim diameter) 6.20  4.21  11.70 Å . In the crystal the [Ni 7 ] units stack on top of one another resulting in a unit cell possessing four psuedo-superimposable 1D columns of [Ni 7 ] units with each unit linked by a 120 rotation. The Fig. 1 (left) Structure of the ligands HL 1 and HL 2 (R ¼ H (L 1), Br (L 2)). (right) Molecular structures of complexes 1 (top) and 2 (bottom) viewed perpendicular and parallel to the [Ni 7 ] plane, respectively.
The occurrence of interpenetration in metal-organic and inorganic networks has been investigated by a systematic analysis of the CSD and ICSD structural databases. For this purpose, a novel version of TOPOS (a program package for multipurpose crystallochemical analysis) has been employed, where the procedure of recognition of interpenetrating nets is based on the representation of a crystal structure as a finite reduced graph. In this paper we report a comprehensive list (301 Refcodes) of interpenetrating metal-organic 3D structures from CSD, that are analyzed on the basis of their topologies. Interesting trends and novel features have been observed and distinct classes of interpenetrating nets have been envisaged, depending on the relationships of the individual motifs.
The synthesis and characterisation of a large family of trimetallic [Mn(III)(3)] Single-Molecule Magnets is presented. The complexes reported can be divided into three categories with general formulae (type 1) [Mn(III)(3)O(R-sao)(3)(X)(sol)(3-4)] (where R = H, Me, (t)Bu; X = (-)O(2)CR (R = H, Me, Ph etc); sol = py and/or H(2)O), (type 2) [Mn(III)(3)O(R-sao)(3)(X)(sol)(3-5)] (where R = Me, Et, Ph, (t)Bu; X = (-)O(2)CR (R = H, Me, Ph etc); sol = MeOH, EtOH and/or H(2)O), and (type 3) [Mn(III)(3)O(R-sao)(3)(sol)(3)(XO(4))] (where R = H, Et, Ph, naphth; sol = py, MeOH, beta-pic, Et-py, (t)Bu-py; X = Cl, Re). We show that deliberate structural distortions of the molecule can be used to tune the observed magnetic properties. In the crystals the ferromagnetic triangles are involved in extensive inter-molecular H-bonding which is clearly manifested in the magnetic behaviour, producing exchange-biased SMMs. These interactions can be removed by ligand replacement to give "simpler" SMMs.
The synthesis and characterisation of a large family of hexametallic [Mn(III)(6)] Single-Molecule Magnets of general formula [Mn(III)(6)O(2)(R-sao)(6)(X)(2)(sol)(4-6)] (where R = H, Me, Et; X = (-)O(2)CR' (R' = H, Me, Ph etc) or Hal(-); sol = EtOH, MeOH and/or H(2)O) are presented. We show how deliberate structural distortions of the [Mn(3)O] trinuclear moieties within the [Mn(6)] complexes are used to tune their magnetic properties. These findings highlight a qualitative magneto-structural correlation whereby the type (anti- or ferromagnetic) of each Mn(2) pairwise magnetic exchange is dominated by the magnitude of each individual Mn-N-O-Mn torsion angle. The observation of magneto-structural correlations on such large polymetallic complexes is rare and represents one of the largest studies of this kind.
The use of alpha-benzoin oxime in Ni(II) chemistry leads to the formation of a family of unusual molecular and supramolecular wheels.
Replacement of carboxylate and solvent with facially capping tripodal ligands enhances the single-molecule magnet (SMM) properties of [Mn(III)3] triangles.
We report the synthesis of a series of mixed valence Mn(II/IV) tetranuclear clusters [Mn(II)2Mn(IV)2O2(heed)2(EtOH)6Br2]Br2 (1), [Mn(II)2Mn(IV)2O2(heed)2(H2O)2Cl4].2EtOH.H2O (2.2EtOH.H2O), [Mn(II)2Mn(IV)2O2(heed)2(heedH2)2](ClO4)4 (3), [Mn(II)2Mn(IV)2O2(heed)2(MeCN)2(H2O)2(bpy)2](ClO4)4 (4) and [Mn(II)2Mn(IV)2O2(heed)2(bpy)2Br4].2MeOH (5.2MeOH). Clusters 1-5 are constructed from the tripodal ligand N,N-bis(2-hydroxyethyl)ethylene diamine (heedH2) and represent rare examples of tetranuclear Mn clusters possessing the linear trans zig-zag topology, being the first Mn(II/IV) mixed-valent clusters of this type. The molecular clusters can then be used as building blocks in tandem with the (linear) linker dicyanamide ([N(CN)2]-, dca-) for the formation of a novel extended network {[Mn(II)2Mn(IV)2O2(heed)2(H2O)2(MeOH)2(dca)2]Br2}n (6), which exhibits a rare form of the 2D herring bone topology.
A multi– high-frequency electron paramagnetic resonance method is used to probe the magnetic excitations of a dimer of single-molecule
magnets. The measured spectra display well-resolved quantum transitions involving coherent superposition states of both molecules.
The behavior may be understood in terms of an isotropic superexchange coupling between pairs of single-molecule magnets, in
analogy with several recently proposed quantum devices based on artificially fabricated quantum dots or clusters. These findings
highlight the potential utility of supramolecular chemistry in the design of future quantum devices based on molecular nanomagnets.
Independent one-, two-, and even three-dimensional nets interpenetrate each other in many solid-state structures of polymeric, hydrogen-bonded nets and coordination polymers. For example, the interpenetration of the adamantane units of two diamondlike nets is shown on the right. A detailed and systematic examination of many interpenetrating nets of this kind is made, and implications for crystal engineering are discussed.
This review describes advances made in three areas of molecular magnetic materials of the types A: extended frameworks (coordination polymers) showing long-range magnetic order, B: spin-coupled clusters with emphasis on single molecule magnets and (n x n) grid species, C: polynuclear spin-switching (spin crossover) compounds of Fe-II with emphasis on dinuclear compounds and one-dimensional (1D) and three-dimensional (3D) (framework) materials, including porous 'hybrid' systems. The work of the author and his group is largely used to provide examples, together with results from other groups and collaborators that are included for comparison and completeness. Supramolecular aspects such as cluster-cluster and chain-chain interactions are discussed where relevant. A brief discussion is also given of the recent studies, carried out elsewhere, dealing with aspects of spintronics and the possible future relevance to molecular computers (type B materials) and with memory and other device possibilities (type C materials)
Self-assembly of new tetranuclear (1) and octanuclear (2) manganese carboxylate clusters is controlled by the bis(bipyridine) ligands L1 and L2, respectively, which are shown on the right. The cation I consists of two Mn2O complex fragments, each of which contains one Mn(II) and one Mn(III) center; 2 contains two butterfly-like Mn4O2 cores linked by bis(bipyridine) bridges. Counterion: ClO4/-.
An attempt to utilize a Co(II) cubanecluster as a building block to create extended frameworks results instead in the transformation of the cube into a dimer of dimers.
The reactions of Ga(acac)3 with salicylaldoxime (saoH2) and methyl-salicylaldoxime (Me-saoH2) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)2] (1) and [Ga(acac)3][Ga(acac)(MesaoH)2] (2), respectively, in high yields. The crystal structures of 1 and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(III) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH− and one bidentate chelate acac− ligands. A [Ga(acac)3] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. 1H and 13C NMR data in CDCl3 indicate that the salicylaldoximato complexes isomerize in solution.
The trinuclear nanomagnet [MnIII3O(Et-sao)3(MeOH)3](ClO4) (1) has been utilized as a building block for the construction of the hexanuclear cluster [{MnIII3O(Et-sao)3(O2CPh)(EtOH)}2{4,4′-bpe}2] (3) that conforms to a rectangle and the two-dimensional coordination polymer {[MnIII3O(sao)3(4,4′-bpe)1.5]ClO4·3MeOH}n (2·3MeOH). The latter exhibits an unprecedented type of entanglement that is based on host guest interactions. The polygon versus the polymer is rationalized in terms of changing an auxiliary anion that influences the arrangement of the potentially “vacant” coordination axes on each MnIII ion of the trinuclear precursor and thereby directing the self-assembly process.
The rational design and self-assembly of complex metallacyclic supermolecules is simply achieved by the use of a strategy based on coordination. The methodology is described, discussed, and illustrated here by various two- and three-dimensional examples, such as the molecular square on the right.
A non-technical account of the links between two-dimensional (2D) hyperbolic and three-dimensional (3D) euclidean symmetric patterns is presented, with a number of examples from both spaces. A simple working hypoth-esis is used throughout the survey: simple, highly symmetric patterns traced in hyperbolic space lead to chemically relevant structures in euclidean space. The prime examples in the former space are derived from Felix Klein's engraving of the modular group structure within the hyperbolic plane; these include various tilings, networks and trees. Disc packings are also derived. The euclidean examples are relevant to condensed atomic and molecular materials in solid-state chemistry and soft-matter structural science. They include extended nets of relevance to covalent frameworks, simple (lattice) sphere packings, and interpenetrating extended frameworks (related to novel coordination polymers). Limited discussion of the projection process from 2D hyperbolic to 3D euclidean space via mapping onto triply periodic minimal surfaces is presented. Manuscript received: 29 July 2003. Final version: 4 August 2003.
The complexes [Mn III 3 O(Et-sao) 3 (O 2 CPh(Cl) 2)(MeOH) 3 (H 2 O)] (1), [Mn III 3 O(Et-sao) 3 (ClO 4)(MeOH) 3 ] (2), [Mn III 3 O(Et-sao) 3 (O 2 Ph(CF 3) 2)(EtOH)(H 2 O) 3 ] (3), and [Mn III 3 O(Ph-sao) 3 (O 2 C-anthra)(MeOH) 4 ]·Ph-saoH 2 (4·Ph-saoH 2) display dominant ferromagnetic exchange interactions leading to molecules with S = 6 ground states. The molecules are sin-gle molecule magnets (SMM) displaying large effective energy barriers for magnetization reversal. In each case their crystal structures reveal multiple intermolecular H-bonding interactions. Single crystal hysteresis loop measurements demonstrate that these interactions are strong enough to cause a clear field bias, but too weak to transform the spin net-works into classical antiferromagnets. These three-dimensional networks of exchange coupled SMMs demonstrate that quantum tunnelling magnetization can be controlled using exchange interactions, suggesting supramolecular chemistry can be exploited to modulate the quantum physics of molecular magnets.
Independent one-, two-, and even three-dimensional nets interpenetrate each other in many solid-state structures of polymeric, hydrogen-bonded nets and coordination polymers. For example, the interpenetration of the adamantane units of two diamondlike nets is shown on the right. A detailed and systematic examination of many interpenetrating nets of this kind is made, and implications for crystal engineering are discussed.
Interpenetration in metal-organic and inorganic networks has been investigated by a systematic analysis of the crystallographic structural databases. We have used a version of TOPOS (a package for multipurpose crystallochemical analysis) adapted for searching for interpenetration and based on the concept of Voronoi-Dirichlet polyhedra and on the representation of a crystal structure as a reduced finite graph. In this paper, we report comprehensive lists of interpenetrating inorganic 3D structures from the Inorganic Crystal Structure Database (ICSD), inclusive of 144 Collection Codes for equivalent interpenetrating nets, analyzed on the basis of their topologies. Distinct Classes, corresponding to the different modes in which individual identical motifs can interpenetrate, have been attributed to the entangled structures. Interpenetrating nets of different nature as well as interpenetrating H-bonded nets were also examined. (c) 2005 Elsevier Inc. All rights reserved.
The use of crystal engineering concepts has produced a variety of coordination networks, many of which exhibit novel and fascinating types of entanglements of individual motifs. This review analyses the structures of a number of entangled polymeric networks reported in these years by many groups. A topological classification of the different interlocked and interweaved species is attempted. Wide classes of polycatenated and polythreaded species have been recognized and other phenomena, as polyknotting (self-penetration) and interweaving of ID chains, are also discussed. Unexpected topological features and new linkages, that were previously overviewed, have been discovered, including the first examples of infinite Borromean links. (C) 2003 Elsevier B.V. All rights reserved.
A number of coordination networks, exhibiting novel and fascinating types of entanglements of individual motifs have been reported throughout the years by many groups. The structural complexity of these species has caused, in some cases, misinterpretations regarding the correct nature of the entanglement. In this article, we analyse the structures of some polymeric networks of the 'polycatenanes' class, which have the peculiar feature of all the constituent motifs having lower dimensionality than that of the overall array. Unexpected topological features and new linkages, that had previously been overlooked, have been discovered. The most relevant finding concerns the first observation of examples of Borromean links in 3D and 2D arrays. These systems are comprised of layers that are not catenated but, nonetheless, inseparably entangled in an uncommon topological fashion.
The synthesis of transition-metal high-spin complexes and of infinite coordination networks of these high-spin carriers now represents a recognized subdiscipline of coordination chemistry. This new research trend has been particularly encouraged by the discoveries that molecular and one-dimensional coordination aggregates may behave as nanomagnets, as illustrated by the so-called single-molecule magnets (SMMs) and single-chain magnets (SCMs). While the synthesis of isolated polynuclear high-spin complexes still rely mostly on serendipitous assembly with appropriate ligands, the synthesis of SCMs or extended networks of high-spin complexes demands a more designed and controlled bottom-up assembly of precursor complexes and bridging species selected for their coordination abilities. In this context, the case of a [Mn4] SMM is unique in the literature, as one-, two-, and three-dimensional networks have been rationally designed by using this SMM unit as a building block, giving rise to original magnetic properties. This review gathers all reported systems that we know of, having the corresponding [Mn4O6] core, either in isolated complexes or in frameworks. Their structures and, when relevant, the synthetic strategy and magnetic properties are described. The demonstrated and potential outcomes, in terms of physical properties, of such coordination assemblies of high-spin complexes are then discussed. These are highlighted through examples with other building blocks, to broaden the scope of possible strategies and building blocks, and thus provide a basis for the further development of this promising area. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
The formation of capsule based architectures on the molecular scale has been of interest to many researchers in recent times. The formation of these assemblies is often challenging and can produce structures on a multi nano-metre scale that can serve specific functions. Some of the approaches used to produce such assemblies are outlined in relation to various building blocks in metal-organic polyhedra, molecular boxes and molecular capsules for example. The last of these has been the focus of our recent studies since the discovery of a hydrogen-bonded nano-capsule based on C-methylresorcin[4]arene, although the molecule also assembles in dimeric capsule motifs. The related pyrogallol[4]arenes display similar behaviour, however a number of metal-organic analogues have recently been synthesised and characterised through a variety of techniques that suggest various assembly processes. These are highlighted in the context of related architectures in order to give a sense of potential for such assemblies that can, in some cases, be assembled instantaneously or very rapidly.
An out-of-plane dimeric MnIII quadridentate Schiff-base compound, [Mn2(salpn)2(H2O)2](ClO4)2 (salpn(2-) = N,N'-(propane)bis(salicylideneiminate)), has been synthesized and structurally characterized. The crystal structure reveals that the [Mn2(salpn)2(H2O)2](2+) units are linked through weak H-bonds (OHwater...OPh) in one dimension along the c-axis, forming supramolecular chains. The exchange interaction between MnIII ions via the biphenolate bridge is ferromagnetic (J/kB = +1.8 K), inducing an ST = 4 ground state. This dinuclear unit possesses uni-axial anisotropy observed in the out-of-plane direction with DMn2/kB = -1.65 K. At low temperatures, this complex exhibits slow relaxation of its magnetization in agreement with a single-molecule magnet (SMM) behavior. Interestingly, the intermolecular magnetic interactions along the one-dimensional organization, albeit weak (J'/kB = -0.03 K), influence significantly the thermally activated and quantum dynamics of this complex. Thus, unique features such as M vs H data with multiple steps, hysteresis effects, and peculiar relaxation time have been explained considering SMMs in small exchange-field perturbations and finite-size effects intrinsic to the chain arrangement. The magnetic properties of this new complex can be regarded as an intermediate behavior between SMM and single-chain magnet (SCM) properties.
We report the synthesis and magnetic characterisation of a series of planar [M₇] (M= Ni(II), Zn(II)) disc complexes [Ni₇(OH)₆(L₁)₆](NO₃)₂ (1), [Ni₇(OH)₆(L₁)₆](NO₃)₂·2MeOH (2), [Ni₇(OH)₆(L₁)₆](NO₃)₂·3MeNO₂ (3), [Ni₇(OH)₆(L₂)₆](NO₃)₂·2MeCN (4), [Zn₇(OH)₆(L₁)₆](NO₃)₂·2MeOH·H₂O (5) and [Zn₇(OH)₆(L₁)₆](NO₃)₂·3MeNO₂ (6) (where HL₁ = 2-iminomethyl-6-methoxy-phenol, HL₂ = 2-iminomethyl-4-bromo-6-methoxy-phenol). Each member exhibits a double-bowl pseudo metallocalix[6]arene topology whereby the individual [M₇] units form molecular host cavities which are able to accommodate various guest molecules (MeCN, MeNO₂ and MeOH). Magnetic susceptibility measurements carried out on complexes 1 and 4 indicate weak exchange between the Ni(II) centres.
Take this ring … Hybrid organic–inorganic rotaxanes can be prepared using a thread incorporating an alkyl ammonium functionality to template the self-assembly of an inorganic wheel cluster. This approach was used to assemble a range of examples, including a system combining two rings and two threads (see picture; C gray, H white, O red, Cu orange, Cr blue-gray, N blue, F light blue).
Insider dealing: Self-assembled hosts applied as “molecular flasks” can alter and control the reactivity and properties of molecules encapsulated within their well-defined, confined spaces. A variety of functional hosts of differing sizes, shapes, and utility have been prepared by using the facile and modular concepts of self-assembly.
The application of self-assembled hosts as “molecular flasks” has precipitated a surge of interest in the reactivity and properties of molecules within well-defined confined spaces. The facile and modular synthesis of self-assembled hosts has enabled a variety of hosts of differing sizes, shapes, and properties to be prepared. This Review briefly highlights the various molecular flasks synthesized before focusing on their use as functional molecular containers—specifically for the encapsulation of guest molecules to either engender unusual reactions or unique chemical phenomena. Such self-assembled cavities now constitute a new phase of chemistry, which cannot be achieved in the conventional solid, liquid, and gas phases.
The reaction of Mn(ClO4)(2).6H2O with Naphth-saoH2 (Naphth-saoH2=2-hydroxy-1-napthaldoxime) in pyridine (py) forms the complex [MnIII3O(Naphth-sao)3(py)3](ClO4).0.5py (.0.5py) in very good yields. Reaction of with NaO2CPh in EtOH produces the complex [MnIII6O2(Naphth-sao)6(O2CPh)2(EtOH)6].[MnIII6O2(Naphth-sao)6(O2CPh)2(EtOH)4].2.5Et2O.0.5H2O (.2.5Et2O.0.5H2O). Further reaction of complex with 1 equivalent of both NaN3 and Mn(ClO4)(2).6H2O in MeOH produces the complex [MnII2MnIII6O2(Naphth-sao)6(N3)6(MeOH)8].10MeOH (.10MeOH) that displays an S approximately 0 ground state. Ligand substitution of Naphth-saoH2 with Me-saoH2 in CH2Cl2-MeOH for the latter complex (Me-saoH2= 2-hydroxyphenylethanone oxime) forms the complex [MnII2MnIII6O2(Me-sao)6(N3)6(MeOH)8].10MeOH (.10MeOH) that displays an S=7 ground state with Ueff= 44.6 K. In all four complexes the main building block is the triangular {MnIII3O(R-sao)3} unit (R=Naphth for , and ; R=Me for ). The ligand substitution in triggers a structural distortion in the [Mn6] sub-core as observed by the increased (Mn-N-O-Mn) torsion angles in , switching the interactions from antiferro- to ferromagnetic, dramatically changing the ground-state of the octanuclear complexes from S=0 to 7.
Use of the dicarboxylates iso-phthalate and succinate in the preparation of [Mn(6)] SMMs links the hexametallic units into 1D chains.
Propelling magnetism: Supramolecular organization leads to a remarkable dodecanuclear {Cu(3)Dy(3)}(2) cluster with a "double-propeller" shape (see picture). The linkages of the CuDy units, both intramolecular and supramolecular, appear to be responsible for a drastic change in the single molecule magnetic behavior.
Coordination-driven self-assembly that combines rigid ditopic Pt(II) metal acceptors and bis-pyridyl organic donors provides a facile means of synthesizing well-defined metallacycles of predetermined size and geometry. Functionalization of the component acceptor or donor building blocks allows for the preparation of multifunctional supramolecular materials wherein the stoichiometry and position of individual functional moieties can be precisely controlled. The design, self-assembly, and applications of polyfunctional supramolecules incorporating functional moieties with host-guest, photonic, materials, and self-organizational properties is discussed.
Metal-organic polyhedra with surface-exposed organic groups have been designed. The polyhedra are based on concentric shells of alternating negative-positive-negative charges and have been used to design homochiral hosts.
The synthesis and magnetic properties of a large family of hexanuclear MnIII SMMs based on the complex [MnIII6O 2(sao)6(O2CH)2(EtOH)4] (saoH2=salicylaldoxime) was investigated. Direct current (dc) magnetization measurements were carried out on polycrystalline samples in a field of 0.1 T and a temperature range of 5-300 K. No attempt was made to fit the data as the crystal structure contained two independent molecules with different geometries. Alternating current susceptibility studies were carried out on crystalline samples in the temperature range 1.8-10.0 K in a 3.5 G field oscillating at frequencies between 50 and 1000 Hz. It was observed that the intermolecular interactions are strong enough to cause a clear field bias, but too weak to transform the spin network into a classical antiferromagnet.
Two types of supramolecular transformations, wherein a self-assembled Pt(II)-pyridyl metal-organic polygon is controllably converted into an alternative polygon, have been achieved through the reaction between cobalt carbonyl and the acetylene moiety of a dipyridyl donor ligand. A [6 + 6] hexagon is transformed into two [3 + 3] hexagons, and a triangle-square mixture is converted into [2 + 2] rhomboids. 1H and 31P NMR spectra are used to track the transformation process and evaluate the yield of new self-assembled polygons. Such transformed species are identified by electrospray ionization (ESI) mass spectrometry. This new kind of supramolecule-to-supramolecule transformations provides a viable means for constructing, and then converting, new self-assembled polygons.
Various present and future specialized applications of magnets require monodisperse, small magnetic particles, and the discovery of molecules that can function as nanoscale magnets was an important development in this regard. These molecules act as single-domain magnetic particles that, below their blocking temperature, exhibit magnetization hysteresis, a classical property of macroscopic magnets. Such 'single-molecule magnets' (SMMs) straddle the interface between classical and quantum mechanical behaviour because they also display quantum tunnelling of magnetization and quantum phase interference. Quantum tunnelling of magnetization can be advantageous for some potential applications of SMMs, for example, in providing the quantum superposition of states required for quantum computing. However, it is a disadvantage in other applications, such as information storage, where it would lead to information loss. Thus it is important to both understand and control the quantum properties of SMMs. Here we report a supramolecular SMM dimer in which antiferromagnetic coupling between the two components results in quantum behaviour different from that of the individual SMMs. Our experimental observations and theoretical analysis suggest a means of tuning the quantum tunnelling of magnetization in SMMs. This system may also prove useful for studying quantum tunnelling of relevance to mesoscopic antiferromagnets.
We provide a summary of our results in three-dimensional, coordination-driven self-assembly based on the directional-bonding methodology, in which the stoichiometric mixing of complementary building blocks, with appropriate, predefined geometries, leads to targeted, nanoscopic cages. Using this motif, we have synthesized high-symmetry ensembles resembling the Platonic solids, such as dodecahedra, and the Archimedean solids, such as truncated tetrahedra and cuboctahedra, as well as other cages, like trigonal bipyramids, adamantanoids, and trigonal prisms. The synthesis and characterization of these compounds is discussed, as is some host-guest chemistry.
A new family of tetranuclear Mn complexes [Mn4X4L4] (H2L = salicylidene-2-ethanolamine; X = Cl (1) or Br (2)) and [Mn4Cl4(L')4] (H2L' = 4-tert-butyl-salicylidene-2-ethanolamine, (3)) has been synthesized and studied. Complexes 1-3 possess a square-shaped core with ferromagnetic exchange interactions between the four Mn(III) centers resulting in an S = 8 spin ground state. Magnetochemical studies and high-frequency EPR spectroscopy reveal an axial magnetoanisotropy with D values in the range -0.10 to -0.20 cm(-1) for complexes 2 and 3 and for differently solvated forms of 1. As a result, these species possess an anisotropy-induced energy barrier to magnetization reversal and display slow relaxation of the magnetization, which is observed as hysteresis for 1 and 3 and frequency-dependent peaks in out-of-phase AC susceptibility measurements for 3. The effective energy barrier was determined to be 7.7 and 7.9 K for 1 and 3, respectively, and evidence for quantum tunneling of the magnetization was observed. Detailed magnetochemical studies, including measurements at ultralow temperatures, have revealed that complexes 1 and 2 possess solvation-dependent antiferromagnetic intermolecular interactions. Complex 3 displays ferromagnetic intermolecular interactions and approaches a ferromagnetic phase transition with a critical temperature of approximately 1 K, which is coincident with the onset of slow relaxation of the magnetization due to the molecular anisotropy barrier to magnetization reversal. It was found that the intermolecular interactions have a significant effect on the manifestation of slow relaxation of the magnetization, and thereby, these complexes represent a new family of "exchange-biased single-molecule magnets", where the exchange bias is controlled by chemical and structural modifications.
A one-dimensional chain of interconnected single-molecule magnets (SMMs) is obtained that consists of [Mn(4)(hmp)(6)](4+) units bridged by chloride ions. Slow magnetization relaxation is evident in the AC susceptibility data and in magnetization hysteresis measurements for [Mn(4)(hmp)(6)Cl(2)](n)(ClO(4))(2)(n). The magnetization hysteresis loops for this complex are similar to those for an SMM and show significant coercive field and steps at regular magnetic intervals. Spin-canted antiferromagnetic coupling due to misalignment of easy axes of neighboring Mn(4) units is also observed for this complex.
Three two-dimensional (2D) network compounds based on Mn(III)/Mn(II) tetranuclear single-molecule magnets (SMMs) connected by dicyanamide (dcn-) linkers have been synthesized: [Mn4(hmp)4(Hpdm)2(dcn)2](ClO4)2 x 2 H2O x 2 MeCN (2), [Mn4(hmp)4Br2(OMe)2(dcn)2] x 0.5 H2O x 2 THF (3), [Mn4(hmp)6(dcn)2](ClO4)2 (4), where Hhmp and H2pdm are 2-hydroxymethylpyridine and pyridine-2,6-dimethanol, respectively. The [Mn4]/dcn- system appears very versatile, but enables its chemistry to be rationalized by a fine-tune of the synthetic conditions. The double cuboidal [Mn4] unit is preserved in the whole family of compounds, despite strong modifications of its Mn(II) coordination sphere. The chemical control of the coordination number of dcn- on the Mn(II) sites has been the key to obtain the following series of compounds: a discrete cluster, [Mn4(hmp)6(NO3)2(dcn)2] x 2 MeCN (1), 2D networks (2, 3, and 4), and the previously reported 3D compound, [Mn4(hmp)4(mu3-OH)2][Mn(II)(dcn)6] x 2 MeCN x THF. Direct current magnetic measurements show that both Mn2+-Mn3+ and Mn3+-Mn3+ intra-[Mn4] magnetic interactions are ferromagnetic leading to an S(T) = 9 ground state for the [Mn4] unit. Despite the very similar 2D lattices in 2-4, the two kinds of orientation of the [Mn4] unit (i.e., angle variations between the two easy axes) lead to different magnetic properties ranging from SMM behavior for 2 and 1 to a long-range canted antiferromagnetic order for 4. Compound 3 is more complicated as the magnetic measurements strongly suggest the presence of a canted antiferromagnetic order below 2.1 K, although the magnetization slow relaxation is simultaneously observed. Heat capacity measurements confirm the long-range magnetic order in 4, while in 3, the critical behavior is frozen by the slow relaxation of the anisotropic [Mn4] units.
Structural distortion in a [Mn-6] complex switches the magnetic exchange from antiferro- to ferromagnetic, resulting in a single-molecule magnet with a record anisotropy barrier.