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01/2013: pages 475-506; , ISBN: 978-1-119-99867-9
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ABSTRACT: The self-assembly of [Cu(II)(dien)(H(2)O)(2)](2+) and [W(V)(CN)(8)](3-) in aqueous solution leads to the formation (H(3)O){[Cu(II)(dien)](4)[W(V)(CN)(8)]}[W(V)(CN)(8)](2)·6.5H(2)O (1). The crystal structure of 1 consists of an unprecedented {[Cu(II)(dien)](4)[W(V)(CN)(8)]}(5+)(∞) chain of (2,8) topology, nonbridging [W(CN)(8)](3-) anions, and crystallization water molecules. The analysis of magnetic behavior of 1 was performed by the density functional theory (DFT) method and magnetic susceptibility measurements. The DFT broken symmetry approach gave two J(CuW) coupling constants: J(ax) = +2.9 cm(-1) assigned to long and strongly bent W-CN-Cu linkage, and the J(eq) = +1.5 cm(-1) assigned to short and less bent W-CN-Cu linkage, located at the axial and the equatorial positions of square pyramidal Cu(II) centers, respectively, in the hexanuclear {W(2)Cu(4)} chain subunit. The dominance of weak-to-moderate ferromagnetic coupling within the chain was confirmed by magnetic calculations. Zero-field susceptibility of the full chain segment {WCu(4)}(n) was calculated by a semiclassical analytical approach assuming that only one W(V) out of five ½ spins of the chain unit WCu(4) is treated as a classical commuting variable. The calculation of the field dependence of the magnetization was performed separately by replacing the same spin with the Ising variable and applying the standard transfer matrix technique. The intermolecular coupling between the chain segments and off-chain [W(CN)(8)](3-) entities was resolved using the mean-field approximation set to be of antiferromagnetic character. The magnetic coupling parameters are compared with those of other low dimensional {Cu(II)-[M(V)(CN)(8)]} systems.
Inorganic Chemistry 03/2011; 50(8):3213-22. · 4.60 Impact Factor
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Michael Griffin,
Stephen Shakespeare,
Helena J Shepherd,
Charles J Harding,
Jean-François Létard, Cédric Desplanches,
Andrés E Goeta,
Judith A K Howard,
Annie K Powell,
Valeriu Mereacre,
Yann Garcia,
Anil D Naik,
Helge Müller-Bunz,
Grace G Morgan
Angewandte Chemie International Edition 01/2011; 50(4):896-900. · 13.45 Impact Factor
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ABSTRACT: An antiferromagnetic interaction of J = -51 cm(-1) has been obtained in a NCS-bridged {Mo(III)-Ni} compound (i.e. [{Mo(NCS)(6)}{NiL}(2)(NCS)](n)), a value twice as large as for the homologous {Cr(III)-Ni} derivative. The DFT calculated spin distribution on {Mo(NCS)(6)}(3-) reveals noticeable spin on the S atoms.
Chemical Communications 10/2010; 46(40):7519-21. · 6.17 Impact Factor
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ABSTRACT: This paper is divided into two parts: in the first part, the influence of solvate molecules on the magnetic properties of spin crossover salts of [Fe(bpp)(2)][Cr(L)(ox)(2)]ClO(4) x nS (bpp = 2,6-bis(pyrazol-3yl)pyridine; L = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen); ox = oxalate dianion; S = solvent) is analyzed. The second part is devoted to the photomagnetic properties of the previously reported [Fe(bpp)(2)][Cr(L)(ox)(2)](2) family of compounds. The study describes the crystal structure, differential scanning calorimetry (DSC) and magnetic properties of [Fe(bpp)(2)][Cr(bpy)(ox)(2)]ClO(4) x EtOH x 4 H(2)O (1) and [Fe(bpp)(2)][Cr(phen)(ox)(2)]ClO(4) x 1.5 EtOH x 4 H(2)O (2). Both salts are high-spin (HS) compounds. Desolvation of 1 yields a material exhibiting a gradual spin crossover that involves 50% of the Fe(2+) cations. Rehydration of this desolvated salt induces a significant increase in the low-spin (LS) population. Desolvation of 2 affords a material showing a more abrupt spin crossover with thermal hysteresis (T(1/2)(increasing) = 286 K and T(1/2)(decreasing) = 273 K). This material is not very sensitive to rehydration. The anhydrous compounds [Fe(bpp)(2)][Cr(bpy)(ox)(2)](2) (3) and [Fe(bpp)(2)][Cr(phen)(ox)(2)](2) (4) display some quantitative photomagnetic conversion with T(LIESST) values of 41 and 51 K, respectively. Kinetic parameters governing the photo-induced HS-LS relaxation process have been determined and used to reproduce the T(LIESST) curves.
Dalton Transactions 10/2009; · 3.84 Impact Factor
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ABSTRACT: An iron(II) complex [Fe(L5)2][ClO4]2 of a new nonplanar tridentate ligand [L5 = 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl](1-methylimidazole)] has been synthesized and its spin-transition properties have been investigated. X-ray structural analysis of the solvated compound [Fe(L5)2][ClO4]2.CH3CN at 100 K and at 298 K revealed a mononuclear Fe(II)N6 pseudooctahedron with the tridentate ligand in the meridional coordination mode. Magnetic susceptibility measurements revealed LS (1A1) <--> HS (5T2) transition starting above room temperature and remained incomplete even up to 350 K, however providing evidence for the hysteretic behaviour of the transition. Photo-magnetic measurements using a 532 nm laser revealed incomplete light-induced excited spin-state trapping (LIESST). Relaxation curves in the dark exhibited a stretched exponential shape, typical for broad distributions of relaxation times. The complete photo-magnetic data were modelled using a non-cooperative master equation including a tunnelling process with distributed parameters and accounting for the bulk absorption of light. We also measured the diffuse reflectance properties, with detailed investigation of the absorption spectra and discussed the obtained features with respect to structural properties, including the suggested presence of disorder.
Dalton Transactions 09/2009; · 3.84 Impact Factor
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ABSTRACT: The thermal and light-induced spin transitions in [FexZn1-x(Phen)2(NCS)2] (Phen = 1,10-phenantholine) have been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and undergo the light-induced excited spin state trapping (LIESST) effect at low temperatures. For each compound, the thermal spin transition temperature, T1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T1/2 decreases with the metal dilution while T(LIESST) remains unchanged. This behaviour is discussed on the basis of the kinetic study performed by combining the use of SQUID magnetometer, up to the T(LIESST) value, and the dynamic diffuse reflectivity setup, from the T(LIESST) temperature up to the thermal spin transition.
Journal of Physics Conference Series 03/2009; 148(1):012026.
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ABSTRACT: We report on the syntheses, crystal structures, and magnetic properties of two cyano-bridged molecular assemblies: [Cu(II)(phen)(3)](2){[Cu(II)(phen)(2)](2)[W(V)(CN)(8)](2)}(ClO(4))(2) x 10 H(2)O (phen = 1,10-phenanthroline) (1) and {[Cu(II)(bpy)(2)](2)[W(V)(CN)(8)]} {[Cu(II)(bpy)(2)][W(V)(CN)(8)]} x 4 H(2)O (bpy = 2,2'-bipyridyl) (2). Compound 1 consists of cyano-bridged [Cu(II)(2)W(V)(2)](2-) molecular rectangles and isolated [Cu(II)(phen)(3)](2+) complexes. The molecular structure of 2 reveals cyano-bridged trinuclear [Cu(II)(2)W(V)](+) and dinuclear [Cu(II)W(V)](-) ions. Magnetic interactions in 1 are interpreted in terms of the model of a tetranuclear moiety consisting of two ferromagnetic Cu(II)-NC-W(V) units (J(1) = +39(4) cm(-1)) interacting antiferromagnetically (J(2) = -1.6(4) cm(-1)). The analysis of the magnetic response of 2 reveals ferromagnetic interaction within the [Cu(II)-NC-W(V)-CN-Cu(II)](+) and [Cu(II)-NC-W(V)](-) isolated units, characterized by J = +35(7) cm(-1) and antiferromagnetic coupling between them (4J' = -0.30(8) cm(-1)). The discussion of the magnetic behavior and the correlation of the J(CuW) parameters with the geometry of cyano bridges at copper(II) centers of 1 and 2 is based on the DFT calculations, which yield J(av) = +13.2 cm(-1) for 1 and J = +31 cm(-1) for 2. The domination of the ferromagnetic Cu(II)-NC-W(V) interaction in 1 and 2 originates from the mutual orthogonality of natural magnetic orbitals in the case of coordination of cyano bridges at the equatorial sites of Cu(II) moieties.
Inorganic Chemistry 03/2009; 48(7):2865-72. · 4.60 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 10/2008; 2008(34):5382 - 5389. · 2.94 Impact Factor
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ABSTRACT: The title compound [Fe (II)(L) 2][ClO 4] 2.C 7H 8 (L = 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl]pyridine) has been isolated while attempting to grow single crystals of the spin-transition (continuous-type) compound [Fe (II)(L) 2][ClO 4] 2, published earlier ( Dalton Trans. 2003, 3392-3397). Magnetic susceptibility measurements, as well as Mossbauer and calorimetric investigations on polycrystalline samples of [Fe(L) 2][ClO 4] 2.C 7H 8 revealed the occurrence of an abrupt HS ( (5) T 2) <--> LS ( (1) A 1) transition with steep and narrow (2 K) hysteresis at approximately 232 K. The photomagnetic properties exhibit features typical for a broad distribution of activation energies, with relaxation curves in the shape of stretched exponentials. We performed a crystal structure determination of the compound at 120, 240, and 270 K. A noteworthy temperature-dependent behavior of the structural parameters was observed, in terms of disorder of both the anions and solvent molecules, leading to a strong thermal dependence of the strength and dimensionality of the interaction network. Additional data were obtained by diffuse reflectance measurements. We model and discuss the antagonistic effects of interactions and disorder by using a two-level cooperative mean-field approach which includes a distribution of barrier energies at the microscopic scale.
Inorganic Chemistry 10/2008; 47(17):7577-87. · 4.60 Impact Factor
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ABSTRACT: A tetranuclear cyano-bridged [{Ni(HL3)}{W(CN)8}]2 compound in a square geometry was formed by self-assembling of {W(CN)8}3- and {NiL3}2+ (L3=pentadentate ligand). The structure of the compound has been established by single crystal X-ray diffraction. The coordination sphere of the Ni ions is severely distorted with the macrocyclic ligand adopting a facial coordination with only four linkages to the metal center. The N atom of the pendant aminopropyl arm of L3 is no longer coordinated to the metal center but has undergone protonation during the assembling process. Magnetic measurements have revealed an unexpected antiferromagnetic behavior (J=-9 cm(-1)), which has been explained using a microscopic many-body electronic model Hamiltonian, based on DFT results. The many-body model is used to fit both the chiMT versus T and the M versus H plots obtained from experiments.
Inorganic Chemistry 07/2008; 47(11):4854-60. · 4.60 Impact Factor
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ABSTRACT: The thermal and light-induced spin transitions in [Fe(x)Zn(1-x)(phen)2(NCS)2] (phen = 1,10-phenantholine) have been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and undergo the light-induced excited spin state trapping (LIESST) effect at low temperatures. For each compound, the thermal spin transition temperature, T1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T1/2 decreases with the metal dilution while T(LIESST) remains unchanged. This behaviour is discussed on the basis of the kinetic study governing the photo-induced back conversion.
Dalton Transactions 06/2008; · 3.84 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 05/2008; 2008(19):2963 - 2966. · 2.94 Impact Factor
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ABSTRACT: A comprehensive study of the photomagnetic behavior of the [Fe(L222N5)(CN)2].H2O complex has been carried out. This complex is characterized by a low-spin (LS) iron(II)-metal center up to 400 K and exhibits at 10 K the well-known Light-Induced Excited Spin State Trapping (LIESST) effect. The critical LIESST temperature (T(LIESST)) has been measured to be 105 K. The kinetics of the transition from the metastable high-spin (HS) state to the low-spin state have been determined and used for reproducing the experimental T(LIESST) curve. This study represents a second example of a fully low-spin iron(II)-metal complex up to 400 K, which can be photoexcited at low temperature with an atypical long-lived metastable HS state. This underlines the preponderant role of the inner coordination sphere for stabilizing the lifetime of the photoinduced HS state.
Inorganic Chemistry 05/2007; 46(10):4114-9. · 4.60 Impact Factor
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ABSTRACT: Two main questions are addressed in this study: (i) What increase of exchange interaction can be expected when replacing a paramagnetic metal ion with a heavier congener located farther down the periodic table (i.e., 3d-4d-5d), and (ii) for a molecular unit with higher coordination numbers, eight in the present case, how is the magnetic information transferred from the metal ion to its ligand set? Qualitative and quantitative investigations on a series of trimetallic cyano-bridged {MoV(CN)8-NiII} and {WV(CN)8-NiII} compounds revealed ferromagnetic interactions but with a strength modulated by the spin organization and their nature. DFT calculations have been used to examine the mechanism and strengths of the exchange coupling, as well as the influence of the local symmetry of the cyanometalate unit on the spin density distribution. Both the experimental and the calculated behaviors underline a noticeable difference between the Mo and the W derivatives (JMoNi = 26.9 cm(-1) and JWNi = 37.3 cm(-1)) that is correlated to the spin density transferred from the metal center to its ligand set. It is also shown that the shape of the {M(CN)8} polyhedron may lead to nonequivalent CN sites and, consequently, to different strengths of the exchange interaction as a result of the position of the bridging ligands.
Journal of the American Chemical Society 09/2006; 128(31):10202-12. · 9.91 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 11/2005; 2006(2):329 - 333. · 2.94 Impact Factor
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ABSTRACT: We have first recalled the T(LIESST) procedure which consists to determine the temperature above which the photo-magnetic effect is erased. In addition we have selected to series of iron(II) spin crossover complexes, the [Fe(PM-L)2(NCS)2] and [Fe(bpp)2]X2nH2O families, to analyse the influence of the cooperativity on the stability of the photo-induced HS state. Some of these complexes exhibit gradual thermal spin crossover behaviours while some others undergo an abrupt thermal transition, with and without hysteresis. Interestingly, whatever the cooperativity effect on the thermal spin crossover transition, the lifetime of the metastable state of all these derivates remains governed by the T(LIESST) = T0 - 0.31 T1/2 relation. Finally, we have investigated the magnetic and the photomagnetic properties of a [Fe(bpp)2]-Nafion film. Once more the role of the cooperativity on the stability of the photoinduced HS state appears minor. Conversely, the influence of the nature and the geometry of the inner coordination sphere appears preponderant.
Journal of Physics Conference Series 09/2005; 21(1):23.
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ABSTRACT: Copper(II) complexes (1-3) of a sterically constrained phenol-based tetradentate N(2)O(2) ligand 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)piperazine (H(2)L) have been reported. The associated anions of the copper(II) ion precursors have profound influence on the stoichiometry of the products. Thus, with perchlorate ion, the product is a binuclear compound [Cu(2)L(2)] (1), while with coordinating anions viz. Cl(-) and N(3)(-), the products [Cu(3)L(2)Cl(2)(H(2)O)].1/2H(2)L (2) and [Cu(3)L(2)(N(3))(2)(CH(3)OH)].4H(2)O (3) have triangulo trinuclear composition. The syntheses, X-ray structures, and spectroscopic and magnetic properties of these complexes are described. Compound 1 has a noncentrosymmetric structure with a rectangular Cu(2)(OPh)(2) core. It appears to be a rare example of a phenolato-bridged Cu(II) dimer exhibiting ferromagnetic interactions (J = 0.93 cm(-)(1)), a behavior in agreement with the theoretical predictions but seldom observed experimentally. In compounds 2 and 3, the copper centers are triangularly disposed, and the molecules have a shape much like that of a butterfly. The terminal copper centers Cu(1) and Cu(2) in 2 and 3 have distorted square pyramidal geometry, connected to each other by a bridging chloro- (in 2) or azido ligand (in 3) in "end to end" fashion. The central copper center (Cu(3) in 2 and Cu in 3) in both the compounds has distorted square planar geometry. The separations between the metal centers, viz. Cu(1)...Cu(2), Cu(2)...Cu(3), and Cu(3)...Cu(1), are 4.826, 3.214, and 3.244 A, respectively, in 2. The corresponding distances in 3 are 5.590, 3.178, and 3.485 A, respectively. The overall magnetic behaviors in 2 and 3 are consistent with antiferromagnetic interactions between the spin centers. In 3, the exchange couplings between the terminal and central copper centers J(Cu(1))(-)(Cu) and J(Cu(2))(-)(Cu) appear to be equal (-234 cm(-)(1)), resulting in an S = (1)/(2) ground state at temperatures near or below 77 K.
Inorganic Chemistry 01/2005; 43(26):8501-9. · 4.60 Impact Factor
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ABSTRACT: A nanosized octadecaheteronuclear aggregate, [[NiL(2)](12)[Nb(CN)(8)](6)(H(2)O)(6)], and a 1-D coordination polymer, [[MnL(1)](2)[Nb(CN)(8)](H(2)O)]( infinity ), have been obtained by self-assembly between the octacyanometalate [Nb(CN)(8)](4)(-) and [ML](2+) complexes. The dimensionality of the supramolecular architectures was found to be controlled by the [ML] module for which the equatorial coordination sites are blocked by a macrocyclic ligand. The crystal structures and magnetic properties for both the compounds are described.
Inorganic Chemistry 11/2003; 42(21):6607-9. · 4.60 Impact Factor
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Inorganic Chemistry 04/2002; 41(5):1323-7. · 4.60 Impact Factor
