-
[show abstract]
[hide abstract]
ABSTRACT: The use of 1-amino-1-cyclohexyl phosphonic acid, a functionalised phosphonate, leads to the synthesis of two new structural types for 3d-4f phosphonate cages with unusual structural cores and which show high magnetocaloric effects.
Chemical Communications 03/2013; · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The pnictogen-centered nucleophiles LiE(SiMe3)2 (E = N, P, or As) substitute a cyclopentadienide ligand of chromocene (Cp2Cr), with elimination of lithium cyclopentadienide, to give the series of pnictogen-bridged compounds [(μ:η2:η5-Cp)Cr{μ-N(SiMe3)2}2Li] (1) and [(η5-Cp)Cr{μ-E(SiMe3)2}]2, with E = P (2) or E = As (3). Whereas 1 is a heterobimetallic coordination polymer, 2 and 3 are homometallic dimers, with the differences being due to a structure-directing influence of the hard or soft character of the bridging group 15 atoms. For compound 1, the experimental magnetic susceptibility data were accurately reproduced by a single-ion model based on high-spin chromium(II) (S = 2), which gave a g-value of 1.93 and an axial zero-field splitting parameter of D = -1.83 cm-1. Determinations of phosphorus- and arsenic-mediated magnetic exchange coupling constants, J, are rare: in the dimers 2 and 3, variable-temperature magnetic susceptibility measurements identified strong antiferromagnetic exchange between the chromium(II) centers, which was modeled using the spin Hamiltonian H = -2J(SCrA·SCrB), and produced large coupling constants of J = -166 cm-1 for 2 and -77.5 cm-1 for 3.
Inorganic Chemistry 03/2013; · 4.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nanoporous crystals formed by the cobalt complex of 2,3,9,10,16,17,23,24-octa(29,69-di-iso-propyphenox-y)phthalocyanine were used to demonstrate in situ coordination chemistry by single-crystal-to-single-crystal transformations. Ligand exchange, including the introduction of imidazole with the apparent simultaneous oxidation of the metal centre, was readily achieved by simply adding the new ligand into the solvent in contact with the Phthalocyanine nanoporous crystals (PNCs). In addition, chloride and bromide axial ligands were introduced by the use of aqueous hydrochloric, hydrobromic acid or bromine as reagents.
CrystEngComm 01/2013; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nanoporous crystals formed by the cobalt complex of 2,3,9,10,16,17,23,24-octa(2',6'-di-iso-propyphenoxy)phthalocyanine were used to demonstrate in situ coordination chem. by single-crystal-to-single-crystal transformations. Ligand exchange, including the introduction of imidazole with the apparent simultaneous oxidn. of the metal center, was readily achieved by simply adding the new ligand into the solvent in contact with the Phthalocyanine nanoporous crystals (PNCs). In addn., chloride and bromide axial ligands were introduced by the use of aq. hydrochloric, hydrobromic acid or bromine as reagents. [on SciFinder(R)]
CrystEngComm 01/2013; 15(8):1545-1550. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An experimental and ab initio computational study of an unsymmetrical, hydride-bridged di-dysprosium single-molecule magnet is reported.
Chemical Communications 12/2012; · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The syntheses of 2,6-di(pyrid-2-yl)pyrazine (L(1)), 2,6-di(pyrazinyl)pyridine (L(2)), 2,2':6',2''-terpyrazine (L(3)), 2,6-di(pyrimidin-4-yl)pyridine (L(4)), 2,6-di(1,2,4-triazin-3-yl)pyridine (L(5)), 4-hydroxy-2,6-di(pyrazinyl)pyridine (L(6)) and 4-hydroxy-2,6-di(pyrimidin-2-yl)pyridine (L(7)) are described. Homoleptic iron(ii) and cobalt(ii) complexes of these ligands have been prepared and, in four cases, structurally characterised. The iron complexes are all low-spin. However, while the cobalt complexes of the pyrazine-rich ligands L(2), L(3) and L(6) are all predominantly low-spin in the solid state, the other cobalt complexes are essentially high-spin between 5-300 K. The voltammetric M(iii)/(ii) (M = Fe or Co) oxidations and metal- or ligand-based reductions all become more anodic as the nitrogen content of the ligands increases, which correlates well with Lever's additive electrochemical parameters for the heterocyclic donor groups in each complex.
Dalton Transactions 11/2012; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The trimetallic complex [{CpMn(μ-OSiPh(3))(2)}(2)Mn] () and the heterocubane [CpMn(μ(3)-SSiPh(3))](4) () are formed by deprotonation of Ph(3)SiQH (Q = O, S) by manganocene, or by transmetallation of manganocene by Ph(3)SiQLi. The Mn(ii) centres in and are antiferromagnetically coupled, with J = -4.4 and -3.0 cm(-1) in and , respectively (-2J formalism).
Dalton Transactions 11/2012; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The iron pivalate clusters [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu (), [Fe(8)(OH)(4)(O(2)C(t)Bu)(12)(OC(6)H(4)C(6)H(5))(8)] () and [Fe(3)O(O(2)C(t)Bu)(6)(C(5)H(5)N)(3)] () have been used as single source precursors to synthesise iron oxide nanoparticles by a hot injection thermal decomposition method in oleylamine, hexadecanol, oleic acid, oleylamine/oleic acid with dodecanol or octyl ether as solvent. The effect of the different reaction parameters such as temperature, reaction time and capping agents on the phase and morphology were studied. The reaction time was studied for () by thermolysis in a mixture of oleylamine, oleic acid, hexadecanol and dodecanol (solvent) at 260 °C. The results obtained showed that a mixture of maghemite-C (Fe(2)O(3)) and magnetite (Fe(3)O(4)) were obtained for aliquots withdrawn for reaction times of less than 30 minutes whilst only magnetite was obtained after one hour. The nanoparticles were characterised by p-XRD, TEM and magnetic measurements. TEM showed that monodispersed magnetite particles were obtained when the precursor was injected at the boiling point of the solvent. The diameter of the monodispersed nanoparticles obtained by the thermolysis of [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu () in oleylamine, hexadecanol, oleic acid with dodecanol or octyl ether as solvent were 4.3 ± 0.4 and 4.9 ± 0.5 nm respectively. Magnetic measurements revealed that all the particles are superparamagnetic.
Dalton Transactions 11/2012; · 3.84 Impact Factor
-
Michael L Baker,
Grigore A Timco,
Stergios Piligkos,
Jennifer S Mathieson,
Hannu Mutka, Floriana Tuna,
Piotr Kozlowski,
Michal Antkowiak,
Tatiana Guidi,
Tulika Gupta,
Harapriya Rath,
Robert J Woolfson,
Grzegorz Kamieniarz,
Robin G Pritchard,
Høgni Weihe,
Leroy Cronin,
Gopalan Rajaraman,
David Collison,
Eric J L McInnes,
Richard E P Winpenny
[show abstract]
[hide abstract]
ABSTRACT: The term "frustration" in the context of magnetism was originally used by P. W. Anderson and quickly adopted for application to the description of spin glasses and later to very special lattice types, such as the kagomé. The original use of the term was to describe systems with competing antiferromagnetic interactions and is important in current condensed matter physics in areas such as the description of emergent magnetic monopoles in spin ice. Within molecular magnetism, at least two very different definitions of frustration are used. Here we report the synthesis and characterization of unusual nine-metal rings, using magnetic measurements and inelastic neutron scattering, supported by density functional theory calculations. These compounds show different electronic/magnetic structures caused by frustration, and the findings lead us to propose a classification for frustration within molecular magnets that encompasses and clarifies all previous definitions.
Proceedings of the National Academy of Sciences 11/2012; · 9.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A series of heteroaromatic bridging ligands are employed in the synthesis of a family of paramagnetic, heterometallic ring dimers. The extent of spin propagation between the rings via the organic conduit is investigated through micro-SQUID magnetometry and EPR spectroscopy from which conclusions over the mechanism of spin-communication are drawn.
Dalton Transactions 07/2012; 41(44):13626-31. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The complex tris(N,N-diethyl-N’-naphthoylselenoureato)iron(III) was synthesised and its X-ray single crystal structure determined. Thermolysis of this complex in oleylamine at all temperatures produced nanocrystals of FeSe2 whereas Aerosol Assisted Chemical Vapour Deposition produced FeSe thin films on silicon substrates. Nanocrystals and thin films were characterised by powder X-ray Diffraction (p-XRD), Scanning Electron Microscopy (SEM), Atomic Force microscopy (AFM), and Transmission Electron Microscopy (TEM).
Journal of Materials Chemistry 06/2012; · 5.97 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The sulfur-bridged dimers [{Cp'(2)Ln(μ-SSiPh(3))}(2)] (Ln=Gd (1), Dy (2); Cp'=η(5)-C(5)H(4)Me) were synthesized by the transmetalation reactions between [Cp'(3)Ln] and Ph(3)SiSLi. Compound 2 is a single-molecule magnet with slow relaxation of magnetization up to 40 K and an anisotropy barrier of U(eff) =133 cm(-1). Insight into the SMM properties of 2 and closely related SMMs has been obtained using ab initio calculations.
Angewandte Chemie International Edition 06/2012; 51(28):6976-80. · 13.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Manganocene reacts with LiE(SiMe(3))(2) (E = P or As) to give [(η(5)-Cp)Mn{μ-E(SiMe(3))(2)}](2), where E = P (1) or As (2). The temperature dependence of the magnetic susceptibility in 1 and 2 is due to antiferromagnetic exchange and to spin-crossover (SCO). Compound 2 shows two-step SCO with hysteresis, involving high-spin (S = 5/2) and intermediate-spin S = (3/2) Mn(II).
Chemical Communications 06/2012; 48(65):8087-9. · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The synthesis, magnetic and electron paramagnetic resonance (EPR) characterisation of isolated, discrete, {Cr
n
III} antiferromagnetically coupled chain complexes is reported for n=6 and 7. Previous studies had reported supramolecular linked {Cr
n
III}
x
species. For n=6, the lowest lying total spin state is diamagnetic with S=1 and 2 first and second excited states, respectively; for n=7, the lowest lying total spin state is S=3/2 with S=1/2 and 5/2 first and second excited states, respectively. The zero-field splittings of these states are well defined by
low-temperature, multi-frequency EPR spectroscopy.
Applied Magnetic Resonance 04/2012; 37(1):685-692. · 0.75 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The electronic structures of [Cu(terpy)(2)](2+) and [Cu(bpp)(2)](2+) (bpp = 2,6-di[pyrazol-1-yl]pyridine) are different, when doped into [M(bpp)(2)][BF(4)](2) (M(2+) = Fe(2+) or Zn(2+)). The [Cu(terpy)(2)](2+) dopant is a typical pseudo-Jahn-Teller elongated copper(II) center. However, the [Cu(bpp)(2)](2+) sites show EPR spectra consistent with a tetragonally compressed {d(z(2))}(1) configuration.
Chemical Communications 03/2012; 48(34):4055-7. · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The synthesis, structures, and magnetic properties of six families of cobalt-lanthanide mixed-metal phosphonate complexes are reported in this Article. These six families can be divided into two structural types: grids, where the metal centers lie in a single plane, and cages. The grids include [4 × 3] {Co(8)Ln(4)}, [3 × 3] {Co(4)Ln(6)}, and [2 × 2] {Co(4)Ln(2)} families and a [4 × 4] {Co(8)Ln(8)} family where the central 2 × 2 square is rotated with respect to the external square. The cages include {Co(6)Ln(8)} and {Co(8)Ln(2)} families. Magnetic studies have been performed for these compounds, and for each family, the maximum magnetocaloric effect (MCE) has been observed for the Ln = Gd derivative, with a smaller MCE for the compounds containing magnetically anisotropic 4f-ions. The resulting entropy changes of the gadolinium derivatives are (for 3 K and 7 T) 11.8 J kg(-1) K(-1) for {Co(8)Gd(2)}; 20.0 J kg(-1) K(-1) for {Co(4)Gd(2)}; 21.1 J kg(-1) K(-1) for {Co(8)Gd(4)}; 21.4 J kg(-1) K(-1) for {Co(8)Gd(8)}; 23.6 J kg(-1) K(-1) for {Co(4)Gd(6)}; and 28.6 J kg(-1) K(-1) for {Co(6)Gd(8)}, from which we can see these values are proportional to the percentage of the gadolinium in the core.
Journal of the American Chemical Society 12/2011; 134(2):1057-65. · 9.91 Impact Factor
-
Thomas B Faust,
Valerio Bellini,
Andrea Candini,
Stefano Carretta,
Giulia Lorusso,
David R Allan,
Laura Carthy,
David Collison,
Rebecca J Docherty,
Jasbinder Kenyon, [......],
Christopher A Muryn,
Harriott Nowell,
Robin G Pritchard,
Simon J Teat,
Grigore A Timco, Floriana Tuna,
George F S Whitehead,
Wolfgang Wernsdorfer,
Marco Affronte,
Richard E P Winpenny
[show abstract]
[hide abstract]
ABSTRACT: We present a synthetic, structural, theoretical, and spectroscopic study of a family of heterometallic ring dimers which have the formula [{Cr(7)NiF(3)(Etglu)(O(2)CtBu)(15)}(2)(NLN)], in which Etglu is the pentadeprotonated form of the sugar N-ethyl-D-glucamine, and NLN is an aromatic bridging diimine ligand. By varying NLN we are able to adjust the strength of the interaction between rings with the aim of understanding how to tune our system to achieve weak magnetic communication between the spins, a prerequisite for quantum entanglement. Micro-SQUID and EPR data reveal that the magnetic coupling between rings is partly related to the through-bond distance between the spin centers, but also depends on spin-polarization mechanisms and torsion angles between aromatic rings. Density functional theory (DFT) calculations allow us to make predictions of how such chemically variable parameters could be used to tune very precisely the interaction in such systems. For possible applications in quantum information processing and molecular spintronics, such precise control is essential.
Chemistry 11/2011; 17(50):14020-30. · 5.93 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Pentagonal-bipyramidal complexes [Co(DABPH)X(H(2)O)]X [X = NO(3) (1), Br (2), I (3)] were synthesized, and their magnetic behavior was investigated. Simulation of the magnetization versus temperature data revealed the complexes to be highly anisotropic (D ≈ +30 cm(-1)) and the magnitude of the anisotropy to be independent of the nature of the axial ligands. The reaction of 1 with K(3)[M(CN)(6)] (M = Cr, Fe) produces the pentametallic clusters [{Co(DABPH)}(3){M(CN)(6)}(2)(H(2)O)(2)] [M = Cr (4), Fe (5)]. Both clusters consist of three {Co(DABPH)} moieties separated by two {M(CN)(6)} fragments. In 4, the central and terminal Co(II) ions are bound to cyanide groups cis to one another on the bridging {Cr(CN)(6)}, whereas in 5, the connections are via trans cyanide ligands, resulting in the zigzag and linear structures observed, respectively. Magnetic investigation revealed ferromagnetic intramolecular interactions; however, the ground states were poorly isolated because of the large positive local anisotropies of the Co(II) ions. The effects of the local anisotropies appeared to dominate the behavior in 5, where the magnetic axes of the Co(II) ions were approximately colinear, compared to 4, where they were closer to orthogonal.
Inorganic Chemistry 11/2011; 50(23):12045-52. · 4.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: [Cp(2)Dy(thf)(μ-Cl)](2) (2) was synthesized from [Cp(2)Dy(μ-Cl)](n), which crystalizes as two polymorphs, with n = 2 (1a) or ∞ (1b). All three compounds show slow relaxation of magnetization, and in 2 the quantum tunnelling was found to be exchange-biased.
Chemical Communications 09/2011; 48(10):1508-10. · 6.17 Impact Factor
-
Michael L Baker,
Stergios Piligkos,
Alberto Bianchi,
Stefano Carretta,
David Collison,
Joseph J W McDouall,
Eric J L McInnes,
Hannu Mutka,
Grigore A Timco, Floriana Tuna,
Prabha Vadivelu,
Høgni Weihe,
Hans U Güdel,
Richard E P Winpenny
[show abstract]
[hide abstract]
ABSTRACT: An investigation into the physical consequences of including a Jahn-Teller distorted Cu(II) ion within an antiferromagnetically coupled ring, [R(2)NH(2)][Cr(7)CuF(8)((O(2)C(t)Bu)(16))] is reported. Inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) spectroscopic data are simulated using a microscopic spin Hamiltonian, and show that the two Cr-Cu exchange interactions must be inequivalent. One Cr-Cu exchange is found to be antiferromagnetic and the other ferromagnetic. The geometry of the Jahn-Teller elongation is deduced from these results, and shows that a Jahn-Teller elongation axis must lie in the plane of the Cr(7)Cu wheel; the elongation is not observed by X-ray crystallography, due to positional disorder of the Cu site within the wheel. An electronic structure calculation confirms the structural distortion of the Cu site.
Dalton Transactions 09/2011; 40(34):8533-9. · 3.84 Impact Factor
