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The old but evergreen family of bimetallic oxalates still offers innovative and interesting results. When (Me4N)3[Cr(ox)3]·3H2O is reacted with MnIIions in a nonaqueous solvent, a novel three-dimensional magnet of the formula [N(CH3)4]6[Mn3Cr4(ox)12]·6CH3OH is obtained instead of the one-dimensional compound obtained in water. This new material exhibits an unprecedented stoichiometry with a binodal (3,4) net topology and the highest critical temperature (TC= 7 K) observed so far in a manganese–chromium oxalate based magnet.

Energy dispersive X-ray diffraction and X-ray absorption spectra of two CoFe Prussian blue analogues were collected under variable pressure at room temperature: one of them is essentially composed of Co IIand Fe IIIions and undergoes a Co II−Fe III→ Co III−Fe IIpressure-induced electron transfer, whereas the other is essentially composed of Co IIIand Fe IIions whatever the pressure. In both compounds, the Co III−Fe IIphase undergoes a structural distortion upon compression. The alkali cation free CoFe Prussian blue analogue, in which the pressure-induced electron transfer occurs, exhibits a more complicated interplay between structural and electronic events. Key interatomic interactions are proposed to account for the pressure behavior of both Co III−Fe IIand Co II−Fe IIIphases.

A new family of 1D cooperative spin-crossover polymers with general formula [{Fe(tba)3}X2]·nH2O [tba = N-(4H-1,2,4-triazol-4-yl)benzamide; X = CF3SO3–, n = 2 (1), n = 0 (4); BF4–,n = 3 (2), n = 0 (5); 4-CH3C6H4SO3–, n = 3 (3), n = 0 (6)] has been synthesised and characterised using a series of spectroscopic methods, X-ray powder diffraction, magnetic susceptibility measurements and differential scanning calorimetry. The copper analogue of 1, [{Cu(tba)3}(CF3SO3)2]·3H2O (7), has also been synthesised and its crystal structure solved at 293 K. Compound 7 crystallises in the P$\bar {1}$ space group. The bidentate N-(4H-1,2,4-triazol-4-yl)benzamide ligand bridges the copper ions through the 1,2-nitrogen positions leading to a one-dimensional infinite polymer. The EXAFS data collected at 80 K for 1 agree perfectly with a linear chain structure, as observed for 7, with [Fe(tba)3] chromophores linked to each other through the adjacent nitrogen atoms of three N-(4H-1,2,4-triazole-4-yl)benzamide ligands. IR spectroscopic studies confirm the retention of the C2v symmetry for the triazole rings in 2 and 3, thereby suggesting a similar chainlike arrangement in these compounds. Compound 1 is low spin (LS) at room temperature while 2 and 3 are high spin (HS). The latter two complexes undergo cooperative thermal spin transition at Tc↓ = 250 and Tc↑ = 258 K in 2 and Tc↓ = 226 and Tc↑ = 238 K in 3. The spin transition in 2 and 3 is accompanied by a change of colour from white in the HS state to violet in the LS state. The thermodynamic parameters associated with the spin transition estimated from DSC measurements are ΔH = 17.8 (2) and 14.6 kJ mol–1 (3), and ΔS = 67.2 (2) and 63.5 J K–1 mol–1 (3). In contrast, the dehydrated compounds 4, 5 and 6 show very different spin-transition behaviour. Complex 4 exhibits an abrupt spin transition centred at room temperature and is accompanied by a relatively large hysteresis loop with a width of 25 K (ΔH = 19.7 kJ mol–1 and ΔS = 65.6 J K–1 mol–1). Like 2 and 3, 4 shows a dramatic colour change upon the spin transition. Complex 5 shows a continuous and incomplete spin transition, and 6 is HS over the whole temperature range investigated (10–400 K). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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Theoretical methods based on density functional theory have been employed to search for Prussian blue analogues with Curie temperatures higher than the ones reached today. Our study suggests several possible cyano‐bridged compounds as candidates to present stronger exchange coupling and higher ordering temperatures than the well known CrIIIVIIderivatives.

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Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)6]³⁻ cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)n(CN&bond;M'L)6−n]^m+ (with n=0–5; M=Cr^III, Co^III, M'=Ni^II; L=pentadentate ligand). Thus, with M=Cr^III, d³, S=3/2, a dinuclear complex [Cr^III(CN)5(CN&bond;NiLn)]⁹⁺, (Ln=polydentate ligand) was built and characterised, showing a spin ground state, SG=5/2, with a ferromagnetic interaction JCr,Cu=+18.5 cm⁻¹. With M=Co^III (d⁶, S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi2, CoNi3, CoNi5 and CoNi6. By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.

Following a bottom-up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)6]³⁻ (M=Cr^III, Co^III) cores to well-defined heptanuclear complexes. By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M=Cr^III, d³, S=3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single-crystal X-ray diffraction and by powder magnetic susceptibility measurements, [Cr^III(CN&bond;M'Ln)6]⁹⁺ (M'=Cu^II, Ni^II, Mn^II, Ln=polydentate ligand), showing spin ground states SG=9/2 [Cu^II], with ferromagnetic interactions JCr,Cu=+45 cm⁻¹, SG=15/2 [Ni^II] and JCr,Ni=+17.3 cm⁻¹, SG=27/2 [Mn^II], with an antiferromagnetic interaction JCr,Mn=−9 cm⁻¹, (interaction Hamiltonian ℋ=−JCr,M [SCrΣiSM(i)], i=1–6). With M=Co^III, d⁶, S=0, the heptanuclear analogues [Co^III(CN−M'Ln)6]⁹⁺ (M'=Cu^II, Ni^II, Mn^II) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'&bond;Co&bond;M'. Supporting information for this article is available on the WWW under http://www.chemeuj.org or from the author.

Following a bottom‐up approach to nanomaterials, we present a rational synthetic route from hexacyanometalates [M(CN)6]3−(M=CrIII, CoIII) cores to well‐defined heptanuclear complexes. By changing the nature of the metallic cations and using a localised orbital model it is possible to control and to tune the ground state spin value. Thus, with M=CrIII, d3, S=3/2, three heptanuclear species were built and characterised by mass spectrometry in solution, by single‐crystal X‐ray diffraction and by powder magnetic susceptibility measurements, [CrIII(CNM′Ln)6]9+(M′=CuII, NiII, MnII, Ln=polydentate ligand), showing spin ground states SG=9/2 [CuII], with ferromagnetic interactions JCr,Cu=+45 cm−1, SG=15/2 [NiII] and JCr,Ni=+17.3 cm−1, SG=27/2 [MnII], with an antiferromagnetic interaction JCr,Mn=−9 cm−1, (interaction Hamiltonian ℋ︁=−JCr,M[SCrΣiSM(i)], i=1–6). With M=CoIII, d6, S=0, the heptanuclear analogues [CoIII(CN−M′Ln)6]9+(M′=CuII, NiII, MnII) were similarly synthesised and studied. They present a singlet ground state and allow us to evaluate the weak antiferromagnetic coupling constant between two next‐nearest neighbours M′CoM′.

Following a bottom‐up approach to nanomaterials, we present a rational synthetic route to high‐spin and anisotropic molecules based on hexacyanometalate [M(CN)6]3−cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X‐ray crystallography and magnetic susceptibility of bi‐, tri‐, tetra‐, hexa‐ and heptanuclear species [M(CN)n(CNM′L)6−n]m+(with n=0–5; M=CrIII, CoIII, M′=NiII; L=pentadentate ligand). Thus, with M=CrIII, d3, S=3/2, a dinuclear complex [CrIII(CN)5(CNNiLn)]9+, (Ln=polydentate ligand) was built and characterised, showing a spin ground state, SG=5/2, with a ferromagnetic interaction JCr,Cu=+18.5 cm−1. With M=CoIII(d6, S=0) were built di‐, tri‐, tetra‐, hexa and hepanuclear CoNi species: CoNi, CoNi2, CoNi3, CoNi5and CoNi6. By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next‐nearest neighbours M′‐Co‐M′.

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One-pot reaction between the dinuclear [Mnii₂(bpym)(H₂O)₈]4+ complex and the mononuclear [Miv(CN)₈]4− unit (M = Mo and W; bpym = 2,2'-bipyrimidine) in aqueous solution yields the novel heterobimetallic complexes of formula {(μ-bpym)[Mn(H₂O)]₂-(μ-NC)₆M(CN)₂} with M = Mo (1) and W (2). 1 and 2 are isostructural three-dimensional compounds where the manganese atoms are bridged by bisbidentate bpym and hexakismonodentate octacyanometalate units. Variable-temperature magnetic susceptibility data of 1 and 2 show the occurrence of a significant antiferromagnetic coupling between the high spin manganese(ii) ions through bridging bpym (J ca. −1.1 cm−1, the exchange Hamiltonian being defined as H = −JS_A·S_B).

The cyano-bridged [CuII(tetrenH₂)]₂[WIV(CN)₈]₂·5H₂O (tetren = tetraethylenepentaamine) (1), [CuII(tetrenH₂)][CuII(tetrenH)][WV(CN)₈][WIV(CN)₈]·2.5H₂O (2), [CuII(dien)]₂[WIV(CN)₈]·4H₂O (dien = diethylenetriamine) (3) and its isomorphous molybdenum(iv) analogue (4) have been prepared and structurally characterised. 1 and 2 are built from the W₂Cu₂(μ-CN)₄ squares extended into 1-D structure by cyano-bridges. 2-D 3 and 4 form a square grid pattern with tungsten atoms in the corners and –CN–Cu(dien)–NC– linkages on the edges of the squares. The magnetic behaviour of 1 and 3 indicates the presence of two isolated CuII spins S = 1/2 with a very weak antiferromagnetic coupling through the diamagnetic NC–WIV–CN bridges in the low temperatures. Assembly 2 exhibits a weak ferromagnetic interaction between CuII and WV isolated by diamagnetic [WIV(CN)₈]4− spacer from another CuII centre within WV–CN–CuII–NC–WIV–CN–CuII unit and the antiferromagnetic interaction between the CuII₂WVWIV units.

The cyano-bridged CuIItetrenH22WIVCN82·5H2O tetren tetraethylenepentaamine 1, CuIItetrenH2CuIItetrenHWVCN8WIVCN8·2.5H2O 2, CuIIdien2WIVCN8·4H2O dien diethylenetriamine 3 and its isomorphous molybdenumiv analogue 4 have been prepared and structurally characterised. 1and 2are built from the W2Cu2μ-CN4squares extended into 1-D structure by cyano-bridges. 2-D 3and 4form a square grid pattern with tungsten atoms in the corners and –CN–Cudien–NC– linkages on the edges of the squares. The magnetic behaviour of 1and 3indicates the presence of two isolated CuIIspins S 12 with a very weak antiferromagnetic coupling through the diamagnetic NC–WIV–CN bridges in the low temperatures. Assembly 2exhibits a weak ferromagnetic interaction between CuIIand WVisolated by diamagnetic WIVCN84−spacer from another CuIIcentre within WV–CN–CuII–NC–WIV–CN–CuIIunit and the antiferromagnetic interaction between the CuII2WVWIVunits.

AbstractThermo or photo-chromic properties can be measured using the light reflected by a surface. An apparatus has been designed for coupling to a SQUID Magnetometer. Instrumental improvements and new results on photo-magnetic systems are reported : (i) Spin crossover system [FexCo1−x(btr)2(NCS)2]·H2O : direct and reverse LIESST, Light Induced Thermal and Optical Hysteresis (LITH/LIOH) (ii) Prussian blue analogue Rb0.52Co[Fe(CN)6]0.84,2.31 H2O : first optical detection of photo-excitation and thermal relaxation of the metastable state.

AbstractUsing the irreducible tensor operator technique we develop a computational approach to the problem of g-tensors for the heteronuclear polymetallic systems consisting of the arbitrary number of coupled paramagnetic ions. We deduce the effective g-values for the family of the heterometallic CrIIINiIIncyanometalates (n=2,3,4,5,6) possessing different topologies. For CrIIINiII6complexes a good fit to experimental μ(T) is achieved. For CrIIICuII6the local anisotropy of g for CuIIions is taken into account.

AbstractPhoto-induced magnetisation has been recently evidenced by Hashimoto et al.in CoFe cyanide[1]. We synthesized a diamagnetic RbFeCo cyanide able to present the same photomagnetic effect. The magnetic properties of the excited state, the electronic structure and the local structure of the ground and the excited states have been investigated. The conditions required to observe the phenomenon and the mechanism of the electron transfer are discussed.

AbstractPrussian blue molecule-based magnets can be designed to exhibit various magnetic properties. One of them based on chromicyanide and vanadium is a magnet at room temperature. Its properties are very sensitive to the synthetic reaction conditions, solvent effects and counterions which can be used to tune the Tc.To study the interaction between nearest metallic neighbours we explore also the influence of diffuse and high energy magnetic orbitals, i.e. 4d or 5d metallic orbitals. Two derivatives of [Wv(CN)8]3-are presented.

Room–temperature magnets belonging to the Prussian blue family were obtained recently through mild chemistry methods, i.e. molecular solution chemistry at room temperature and pressure. The paper describes the rational way followed to reach this goal and the prospects opened. First, the structure of Prussian blues and how it allows variation of the electronic structure and exchange interaction through the cyanide bridge is recalled. Then it is shown how the systematic use of orbital models and simple semiempirical calculations, combined with the Néel molecular field approach, helps in increasing the Curie temperature up to room temperature in vanadium–chromium derivatives. Some methods are then proposed to improve the magnetic properties and some examples of applications in demonstrators, devices, photomagnetism, etc, are given. Finally, we mention some exciting challenges in molecular magnetism, including the preparation of single molecule magnets at room temperature.

A recently developed computational strategyis applied to examine the influence of several factors on the exchange coupling constants of oxalato‐bridged copper(II) binuclear complexes (shown schematically here); molecular topology, the nature of terminal ligands and selected structural parameters are discussed.

The spin density distribution in transition metal complexes is discussed in qualitative terms, taking into account the coexistence of spin delocalization and spin polarization mechanisms, with the help of numerical results for several complexes obtained from density functional calculations. The covalent character of the metal-ligand bonds as well as the σ- or π-characteristics of the partially filled d orbitals must be taken into account to qualitatively predict the sign of the spin density at a particular atom within a ligand. The same patterns can be applied to binuclear complexes and can be helpful in determining the ferro- or antiferromagnetic character of the exchange coupling between two paramagnetic ions when the energy gap between the partially occupied molecular orbitals is small. An attempt is made to establish a link between the qualitative-Hay-Thibeault-Hoffmann model of exchange coupling and the of spin polarization model.

Clusters which display the rare cubic Fe8topology have been obtained by reaction of the metastable hexavacant polyoxotungstate H2P2W12O4812−with basic trinuclear metal acetates.

In this short communication we describe the synthesis and the optical and magnetic properties of optically active three dimensional (3D) bimetallic [Cr-Mn] networks {[ΔCr^IIIΔMn^II(ox)3][ΔRu^II(bpy)3]ClO4}n1 − Δ, {[ΛCr^IIIΛMn^II(ox)3][ΛRu^II (bpy)3]ClO4}n 1 − Λ and {[ΔCr^IIIΔMn^II(ox)3][ΔRu^II(bpy)2p p y]}n 2 − Δ,{[ΛCr^IIIΛMn^II(ox)3][ΛRu^II(bpy)2ppy]}n 2 − Λ (ox = oxalate, bpy = bipyridine, ppy = phenyl-pyridine). Chirality 13:712–714, 2001. © 2001 Wiley-Liss, Inc.

In this short communication we describe the synthesis and the optical and magnetic properties of optically active three dimensional (3D) bimetallic [Cr‐Mn] networks {[ΔCrIIIΔMnII(ox)3][ΔRuII(bpy)3]ClO4}n1− Δ, {[ΛCrIIIΛMnII(ox)3][ΛRuII(bpy)3]ClO4}n1− Λ and {[ΔCrIIIΔMnII(ox)3][ΔRuII(bpy)2p p y]}n2− Δ,{[ΛCrIIIΛMnII(ox)3][ΛRuII(bpy)2ppy]}n2− Λ (ox = oxalate, bpy = bipyridine, ppy = phenyl‐pyridine). Chirality 13:712–714, 2001. © 2001 Wiley‐Liss, Inc.

Reaction of FeiiibipyCN4−with fully solvated Miications M Co 1 and Mn 2 produces the isostructural bis double zigzag chains FeiiibipyCN42MiiH2O·MeCN·½H2O; 1exhibits intrachain ferromagnetic and interchain antiferromagnetic couplings, slow magnetic relaxation and hysteresis effects.

Reaction of [Feiii(bipy)(CN)₄]− with fully solvated Mii cations [M = Co (1) and Mn (2)] produces the isostructural bis double zigzag chains [[Feiii(bipy)(CN)₄]₂Mii(H₂O)]·MeCN·½H₂O; 1 exhibits intrachain ferromagnetic and interchain antiferromagnetic couplings, slow magnetic relaxation and hysteresis effects.

Crystals of (H3O){[Cu(dien)]4[W(CN)8]} [W(CN)8]2·6.5H2O (dien: diethylenetriamine) are prepared by slow diffusion of aqueous solutions of [Cu(dien)(H2O)2]Cl2and Cs3[W(CN)8] in an H‐tube at room temperature (pH 5.5, 22% yield).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

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