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ABSTRACT: We demonstrate the use of a Cu(I) catalyzed "Click" reaction in the synthesis of novel ligands for spin crossover complexes. The reaction between azides and alkynes was used to synthesize the reported tripodal ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBTA, and the new ligands tris[(1-cyclohexyl-1H-1,2,3-triazol-4-yl)methyl]amine, TCTA, and tris[(1-n-butyl-1H-1,2,3-triazol-4-yl)methyl]amine, TBuTA. Reactions of TBTA with Co(ClO(4))(2) lead to complexes of the form [Co(TBTA)(CH(3)CN)(3)](ClO(4))(2), 1, and [Co(TBTA)(2)](ClO(4))(2), 2, where complex formation can be controlled by the metal/ligand ratio and the complexes 1 and 2 can be chemically and reversibly switched from one form to another in solution resulting in coordination ambivalence. The benzyl substituents of TBTA in 2 show intramolecular C-H-π T-stacking that generates a chemical pressure to stabilize the low spin (LS) state at lower temperatures. The structural parameters of 2 are consistent with a Jahn-Teller active LS Co(II) (elongation) ion showing four short and two long bonds. 2 shows spin-crossover (SCO) behavior in the solid state and in solution with a high T(0) close to room temperature which is driven by the T-stacking. 1 remains high spin (HS) between 2 and 400 K. Reversible chemical switching is observed between 1 and 2 at room temperature, with an accompanying change in the spin state from HS to LS. The importance of the intramolecular T-stacking in driving the SCO behavior is proven by comparison with two analogous compounds that lack an aromatic substituent and remain HS down to very low temperatures.
Inorganic Chemistry 07/2011; 50(13):6114-21. · 4.60 Impact Factor
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ABSTRACT: Among iron 122 pnictide superconductors, the EuFe$_2$As$_2$ series draws
particular interest because, in addition to superconductivity or the long-range
spin-density-wave order in the Fe subsystem, the localized Eu$^{2+}$ magnetic
moments order at low temperatures. Here we present a novel scheme of how the
spins align in the Eu compounds when pressure varies the coupling; we explain
magnetization measurements on EuFe$_2$(As$_{1-x}$P$_x$)$_2$ single crystals as
well as other observations of the Eu$^{2+}$ ordering previously reported in
literature. The magnetic moments of the Eu$^{2+}$ ions are slightly canted even
in the parent compound EuFe$_2$As$_2$, yielding a ferromagnetic contribution
along the $c$-direction that becomes stronger with pressure. Reducing the
interlayer distance even further, the antiferromagnetic coupling of the $ab$
planes finally turns ferromagnetic.
03/2011;
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Advanced Materials 09/2010; 22(36):4054-8. · 13.88 Impact Factor
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Chemistry 02/2010; 16(10):2977-81. · 5.93 Impact Factor
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ABSTRACT: A new heteroleptic bis(phthalocyaninato) terbium(III) complex 1, bearing a pyrenyl group, exhibits temperature and frequency dependence of ac magnetic susceptibility, typical of single-molecule magnets. The complex was successfully attached to single-walled carbon nanotubes (SWNTs) using pi-pi interactions, yielding a 1-SWNT conjugate. The supramolecular grafting of 1 to SWNTs was proven qualitatively and quantitatively by high-resolution transmission electron microscopy, emission spectroscopy, and atomic force spectroscopy. Giving a clear magnetic fingerprint, the anisotropy energy barrier and the magnetic relaxation time of the 1-SWNT conjugate are both increased in comparison with the pure crystalline compound 1, likely due to the suppression of intermolecular interactions. The obtained results propose the 1-SWNT conjugate as a promising constituent unit in magnetic single-molecule measurements using molecular spintronics devices.
Journal of the American Chemical Society 10/2009; 131(42):15143-51. · 9.91 Impact Factor
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ABSTRACT: A mixed theoretical and experimental approach was used to determine the local magnetic anisotropy of the dysprosium(III) ion in a low-symmetry environment. The susceptibility tensor of the monomeric species having the formula [Dy(hfac)(3)(NIT-C(6)H(4)-OEt)(2)], which contains nitronyl nitroxide (NIT-R) radicals, was determined at various temperatures through angle-resolved magnetometry. These results are in agreement with ab initio calculations performed using the complete active space self-consistent field (CASSCF) method, validating the predictive power of this theoretical approach for complex systems containing rare-earth ions, even in low-symmetry environments. Susceptibility measurements performed with the applied field along the easy axis eventually permitted a detailed analysis of the temperature and field dependence of the magnetization, providing evidence that the Dy ion transmits an antiferromagnetic interaction between radicals but that the Dy-radical interaction is ferromagnetic.
Journal of the American Chemical Society 04/2009; 131(15):5573-9. · 9.91 Impact Factor
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Angewandte Chemie International Edition 01/2009; 48(4):746-50. · 13.45 Impact Factor
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ABSTRACT: A revolution in electronics is in view, with the contemporary evolution of the two novel disciplines of spintronics and molecular electronics. A fundamental link between these two fields can be established using molecular magnetic materials and, in particular, single-molecule magnets. Here, we review the first progress in the resulting field, molecular spintronics, which will enable the manipulation of spin and charges in electronic devices containing one or more molecules. We discuss the advantages over more conventional materials, and the potential applications in information storage and processing. We also outline current challenges in the field, and propose convenient schemes to overcome them.
Nature Material 04/2008; 7(3):179-86. · 32.84 Impact Factor
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ABSTRACT: Hybrid mixed metal oxalates of general formula [M(2)(III)M(II)(C(2)O(4))(6)][DAMS](4)center dot 2DAMBA center dot 2H(2)O, where M(III) = Rh, Fe, Cr; M(II) = Mn, Zn; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium, belong to a new family of multifunctional materials displaying both very high second harmonic generation (SHG) efficiency and tunable magnetic properties. Here we report on the preparation and magnetic characterization of the new Ni(II) members of this family. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II) and Mn(II), thus preserving the very high NLO efficiency but allowing further significant tuning of the magnetic properties. In particular the delocalization of Ni(II) magnetic orbitals along the inorganic "stripes" of the crystalline network produces strong next-nearest-neighbor magnetic interactions, otherwise absent in the chains of compounds containing the Mn(II) ions. Such interactions, when in the presence of magnetic M(III) ions such as Cr(III) or Fe(III), give rise to an interesting and complex magnetic behavior possibly due to an almost perfect compensation between nearest-neighbor and next-nearest-neighbor interactions along the chain. (C) 2008 Elsevier B.V. All rights reserved.
Inorganica Chimica Acta 01/2008; 361(14-15):4004-4011. · 1.85 Impact Factor
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Elena Cariati,
Roberto Macchi,
Dominique Roberto,
Renato Ugo,
Simona Galli,
Nicola Casati,
Piero Macchi,
Angelo Sironi, Lapo Bogani,
Andrea Caneschi,
Dante Gatteschi
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ABSTRACT: Mixed M(II)/M(III) metal oxalates, as "stripes" connected through strong hydrogen bonding by para-dimethylaminobenzaldeide (DAMBA) and water, form an organic-inorganic 2D network that enables segregation in layers of the cationic organic NLO-phore trans-4-(4-dimethylaminostyryl)-1-methylpyridinium, [DAMS+]. The crystalline hybrid materials obtained have the general formula [DAMS]4[M2M'(C2O4)6].2DAMBA.2H2O (M = Rh, Fe, Cr; M' = Mn, Zn), and their overall three-dimensional packing is non-centrosymmetric and polar, therefore suitable for second harmonic generation (SHG). All the compounds investigated are characterized by an exceptional SHG activity, due both to the large molecular quadratic hyperpolarizability of [DAMS+] and to the efficiency of the crystalline network which organizes [DAMS+] into head-to-tail arranged J-type aggregates. The tunability of the pairs of metal ions allows exploiting also the magnetic functionality of the materials. Examples containing antiferro-, ferro-, and ferri-magnetic interactions (mediated by oxalato bridges) are obtained by coupling proper M(III) ions (Fe, Cr, Rh) with M(II) (Mn, Zn). This shed light on the role of weak next-nearest-neighbor interactions and main nearest-neighbor couplings along "stripes" of mixed M(II)/M(III) metal oxalates of the organic-inorganic 2D network, thus suggesting that these hybrid materials may display isotropic 1D magnetic properties along the mixed M(II)/M(III) metal oxalates "stripes".
Journal of the American Chemical Society 09/2007; 129(30):9410-20. · 9.91 Impact Factor
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ABSTRACT: A control of the dynamics of the magnetisation is chemically achieved in a ring-like Dy-radical based molecule, allowing the estimation of the quantum tunneling frequency with a (4)He-cooled susceptometer.
Chemical Communications 06/2007; · 6.17 Impact Factor
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ABSTRACT: The first family of rare-earth-based single chain magnets is presented. Compounds of general formula [M(hfac)3(NITPhOPh)], where M = Eu, Gd, Tb, Dy, Ho, Er, or Yb, and PhOPh is the nitronyl-nitroxide radical (2,4'-benzoxo-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), have been structurally characterized and found to be isostructural. The characterization of both static and dynamic magnetic properties of the whole family is reported. Dy, Tb, and Ho compounds display slow relaxation of the magnetization, and ac susceptibility shows a thermally activated regime with energy barriers of 69, 45, and 34 K for Dy, Tb, and Ho compounds, respectively, while only a frequency-dependent susceptibility is observed for Er below 2.0 K. In Gd and Yb derivatives, antiferromagnetic interactions dominate. The pre-exponential factors differ by about 4 orders of magnitude. Finite size effects, due to naturally occurring defects, affect the static and dynamic properties of the compounds differently.
Journal of the American Chemical Society 07/2006; 128(24):7947-56. · 9.91 Impact Factor
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Angewandte Chemie International Edition 10/2005; 44(36):5817-21. · 13.45 Impact Factor
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ABSTRACT: The second-order nonlinear optical properties of a family of rare-earth-based single chain magnets are presented (using a fundamental field at wavelength l = 766 nm), together with an analysis of the origin of the second-harmonic generation (SHG) process. By studying the fundamental crystal symmetries and the geometrical arrangement of the constituting elements of the system in the unit cell we show that the main contribution to the nonlinear process arises from intermolecular p-stacking interactions.
Journal of material chemistry.
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ABSTRACT: We demonstrate that van der Waals interactions can be used to self-assemble a small, controlled number of magnetic nanoparticles onto metallic and semiconducting carbon nanotubes. We study the effect of the sequential grafting on the room temperature transport properties of carbon-nanotube electronic devices containing metallic or semiconducting carbon nanotubes. The results show that the grafting of the nano-objects has different effects on metallic and semiconducting CNTs, with an appreciable effect for single nanoparticle grafting only on field effect transistors. The results indicate that these grafting techniques are suited for the production of multi-quantum dot systems usable at low temperatures. Magnetization measurements of single nano-objects using carbon nanotube-based magnetic sensors, like nano-SQUID devices, also become feasible. Obtaining electronic devices constituted of a few nano-objects with different functionalities is an essential issue of modern electronics 1 and in the emerging field of molecular spintronics, 2 where a controlled number of nanomagnets must be coupled to an electronic nanodevice. Systems with a quantized energy spectrum, called quantum dots (QDs), can be considered as artificial atoms and display quantum transport properties. 3 One way to perform molecular spintronic measurements is to use break junctions, in which a single magnetic molecule or QD is sandwiched between two metallic electrodes inside a nanometre-sized gap. 2 Another possibility is to use the tip of a scanning tunneling microscope to let a current flow through the molecule or QD. All such measurements descend from single molecule trans-port experiments, and can rely on previous experience and back-ground. Anyway in these detection schemes the electron flow interacts strongly with the probed system, even altering its oxida-tion state. Such changes could be exploited, in molecular magnets, to observe interesting physical effects, e.g. negative differential conductance, 4 but undoubtedly alter the magnetic state of the probed system. In contrast, it is important, e.g. to perform quantum computation experiments, to be able to probe the magnetization of a magnetic QD without interacting too strongly with it. Under this perspective it must be noticed that in spintronic experiments, unlike purely electrical transport spectroscopy, we do not necessarily need to flow the electrons through the molecule. If the magnetization of the nanomagnet can affect the electron flow through a nearby object, then we can probe the magnetization of the single object without strongly altering the magnetic state. This detection scheme uses what we called a spintronic double-dot, 2 and a proposed implementation exploits the particular properties of carbon nanotubes (CNTs). 2 CNTs constitute one-dimensional conducting nanowires and are appealing constituents for such double-dot hybrids as they behave, in small junctions, as QDs. 5 They display semi-conducting or metallic behaviour, depending on their structural characteristics. It is thus possible to build a variety of circuits from single CNTs, and obtain CNT-based field effect transistors (CNT-FETs) 6 or CNT-based superconducting quantum inter-ference devices (CNT-SQUIDs), 7 depending on the contacts used and the CNT connected. The absence of an outer oxide layer, normally present on nanowires and on most inorganic nano-structures, makes such devices particularly sensitive. CNT devices thus constitute extremely sensitive probes for chemical and biological applications 8,9 and CNT-based SQUIDs are, in principle, sensitive enough to probe the magnetization of a single nanoparticle (NP), molecule or atom. 7 With one magnetic QD in the multi-dot device, such CNT-based circuits could be used for molecular spintronics experiments, 2 provided that the QDs interact only weakly, thus retaining their identity. 2,7 Coupling a single, integrated CNT with a controlled number of nanomagnets, thus forming a multi-dot device, is a fundamental step towards information processing and advanced nano-electronics. 10 The controlled assembly of multi-dots is still a challenging task, and the inclusion of a magnetic QD is almost unconsidered. Chemical methods have produced double-and multi-dots useful for optical investigation 11 and multi-QDs suit-able for transport measurements have been created with litho-graphic techniques. 12 Anyway scaling these fabrication processes up to more than a few QDs has proved to be a formidable task, and the processes are usually not suited to magnetic materials. Thus new ways have to be explored for molecular spintronics.
