Photo-induced magnetization in copper(II) octacyanomolybdate(IV)

The photomagnetic effect of the mixed-valence compound Cu₂^II[Mo^IV(CN)₈]·7.6H₂O (Cu^II; 3d⁹, S=1/2, Mo^IV; 4d², S=0) (1) was investigated. The UV–VIS spectra showed the intervalence transfer (IT) band between Mo^IV–CN–Cu^II and Mo^V–CN–Cu^I around 500 nm. When the paramagnetic compound 1 was irradiated by a filtered blue light (400–430 nm, 3 mW/cm²) of a Xe lamp at 5 K, the irradiated sample exhibited a spontaneous magnetization with a Curie temperature of 17 K. By annealing the irradiated sample above 200 K, the magnetic property of this sample returned to the initial state. This photo-induced magnetization is explained by the following mechanism. The excitation of the IT band causes the electron transfer from Mo^IV (S=0) to Cu^II (S=1/2), producing a mixed-valence isomer of Mo^V (S=1/2)–CN–Cu^I (S=0). However, half of the copper ions remain as Cu^II ions due to the stoichiometric limitation and hence the irradiated 1 is expressed as Cu^ICu^II[Mo^V(CN)₈]·7.6H₂O. The unpaired electrons on Mo^V (S=1/2) ions and those on Cu^II (S=1/2) ions in the irradiated compound interact ferromagnetically, giving rise to the spontaneous magnetization.     

Crystalline patterns and band structure dimensionality in a series of conducting hybrids associating amide-functionalized EDT-TTF π-donors with the isosteric octahedral anions [FeNO(CN)5]2− and [M(CN)6]3− (M = Co,Fe)

Four new radical cation salts based on the amide functionalized EDT-TTF organic donors EDT-TTF-CONH₂ (D1) and EDT-TTF-(CONH₂)₂ (D2), α′-(D1)₄[FeNO(CN)₅] (1), α′-(D1)₄[Co(CN)₆] (2), β-(D1)₆[Fe(CN)₆] (3) and (D2)₄[FeNO(CN)₅]NB (4), have been synthesized and characterized by X-ray single crystal diffraction experiments, band structure calculations and electrical resistivity measurements. Functionalized organic donors are remarkable for the ability to form cation⋯cation and cation⋯anion type hydrogen bonds which can effectively direct the crystal architecture of molecular conductors. The structural analysis reveals a well-developed hydrogen bond network in the crystals investigated. (D1)₂-dimers or (D2)_n-extended zigzag chains of donors connected through functional groups are found to be stable structural motifs in 1–4. Remarkably, salts 1 and 2 are isostructural despite the presence of anions of different charge (−2 and −3, respectively) and the inherent difference in the degree of charge transfer has a clear effect on the transport properties: σ_RT(2)/σ_RT(1) = 300. Salt 3 differs from 1 and 2 both in the stoichiometry and packing of the conducting organic layer. Crystals of 4 exhibit a superstructure with the incommensurate vector q = ±(0.5, 0.3, 0.2).     

Multi-component molecular conductors with supramolecular assembly based on ET radical cation salts with (NO3)− anion

Synthesis, structure and conducting properties of two new multi-component radical cation ET salts with the (NO₃)⁻ counterion: (ET)₂(NO₃)·C₂H₄(OH)₂ (I) and (ET)₂(NO₃)·0.5[C₂H₄(OH)₂]·H₂O (II) are described. Both salts have layered structures with the distinguishing feature of hydrogen bonds being present between the radical cation layers and anion sheets. It was found that introduction of glycol molecules to compositions of I and II significantly affects the structure of their cation and anion layers and, as a result, their conducting properties. I is a semiconductor, while II demonstrates metallic conductivity down to 4.2 K.     

Study on the boundary structures in a series of lanthanide hexacyanoferrate(III) n-hydrates

The properties of a series of lanthanide hexacyanoferrate(III) n-hydrates were studied by means of thermal analysis, IR spectroscopy, Raman spectroscopy and X-ray crystallography. Thermal analyses showed that there were two kinds of complexes in this series, Ln[Fe(CN)₆]·5H₂O (Ln=La–Nd) and Ln′[Fe(CN)₆]·4H₂O (Ln′=Sm–Lu). The boundary complex between them was Nd[Fe(CN)₆]·5H₂O. The IR spectra of the two kinds of complexes were obviously different. For the pentahydrates, there were two sharp CN stretching bands at 2050 and 2140 cm⁻¹, and one band at 1600 cm⁻¹ assigned to the HOH bending. On the other hand, for the tetrahydrates besides the two CN stretching bands at 2050 and 2140 cm⁻¹, a new band was observed at 1940 cm⁻¹, and the HOH bending band split into three bands around 1600 cm⁻¹. From the X-ray crystal analysis, the structure of the boundary complex Nd[Fe(CN)₆]·5H₂O was determined. It belonged to hexagonal, P6₃/m, with a=7.467(2) Å, c=13.793(3) Å and Z=2 (R=0.082, R_w=0.126). Neodymium was nine-coordinated in the form of the NdN₆(H₂O)₃ group. The three coordinated water molecules of the 5H₂O complex with Nd have a large value for the equivalent isotropic thermal parameter. One of the three water molecules was dissociated easily and the 5H₂O complex changed into the stable 4H₂O complex with Nd. The crystal of the 4H₂O complex is orthorhombic, and belongs to the space group Cmcm as well as the other Ln[Fe(CN)₆]·4H₂O (Ln=Sm–Lu). Therefore, the structure of Nd[Fe(CN)₆]·5H₂O is regarded as the boundary structure.     

Conductive complexes of [Ni(dmid)2] with TTF,TMTTF, and ET

Three charge-transfer salts of [Ni(dmid)₂]⁻ (dmid: 1,3-dithiol-2-one-4,5-dithiolate)—TMTTF[Ni(dmid)₂], TTF_x[Ni(dmid)₂] and ET_x[Ni(dmid)₂] (TMTTF: tetramethyl-tetrathifulvalene, TTF: tetrathifulvalene, ET: bis(ethylenedithio)-tetrathiafulvalene) are prepared and characterized. The TMTTF[Ni(dmid)₂] complex has a structure with mixed packs is formed by cations and anions, which alternate each other with subsequent shift. This compound is semiconductor with the room-temperature conductivity of 2.2 × 10⁻³ Ω⁻¹ cm⁻¹. The TTF_x[Ni(dmid)₂] and ET_x[Ni(dmid)₂] complexes have a highest conductivity: σ_RT 1.86 and 0.54 Ω⁻¹ cm⁻¹, respectively.     

Ferromagnetism and its photo-induced effect in 2D iron mixed-valence complex coupled with photochromic spiropyran

Iron mixed-valence complex, (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] (dto = C₂O₂S₂), shows a spin-entropy driven phase transition called charge transfer phase transition around 120 K and a ferromagnetic transition at 6.5 K. These phase transitions remarkably depend on the hexagonal ring size in two-dimensional honeycomb network structure of [Fe^IIFe^III(dto)₃]_∞. In order to control the magnetic properties and the electronic state in the dto-bridged iron mixed-valence system by means of photo-irradiation, we have synthesized a photo-sensitive organic–inorganic hybrid system, (SP)[Fe^IIFe^III(dto)₃] (SP = spiropyran), and investigated the photo-induced effect on the magnetic properties by the measurements of magnetic susceptibility, ESR, IR, UV–vis and ⁵⁷Fe Mössbauer spectra. Upon UV irradiation at 337 nm, a broad absorption band between 500 nm and 600 nm appears and continuously increases with the photo-irradiation time, which implies that the UV irradiation changes the structure of spiropyran from closed form to open one in solid state. The photochromism in spiropyran changes the ferromagnetic transition temperature and the coercive force.     

Structural and magnetic properties of metal complexes constructed by pyridine-2,6-dicarboxylate and 5-(4-bromophenyl)-2,4′-bipyridine

Pyridine-2,6-dicarboxylic acid reacts as the first ligand (L1) under hydrothermal conditions with different metal ions such as Co^II, Ni^II, and Cu^II to form two 1D polymeric complexes [M(L1)(L2)₂·H₂O]_n (M = Co²⁺ or Ni²⁺) and a tetranuclear cluster with formula [Cu₄(L2)₄(L1)₄]·2H₂O in the presence of 5-(4-bromophenyl)-2,4′-bipyridine as the second ligand (L2). Intramolecular interactions were observed in the three compounds, being antiferromagnetic in both cobalt and nickel 1D coordination polymers and ferromagnetic interaction in the tetranuclear copper cluster.     

Solid state electrical conductance properties of some new bimetallic salts and heterometallic coordination polymers derived from bis (1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolato) cuprate(II) ion

This paper describes the solid state conductivity of the salt [n-Bu₄N]₂[Cu(ecda)₂], bimetallic salts of the type, [M(diimine)₃][Cu(ecda)₂] and heterobimetallic coordination polymers, Pd[Cu(ecda)₂] and Ag₂[Cu(ecda)₂] (M=Fe(II), Co(II), Ni(II), or Cd(II); diimine=1,10-phenanthroline (phen) or ethylenediamine (en) and ecda²⁻=1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate) that have been synthesized and investigated using molecular spectroscopies. A unique feature of [n-Bu₄N]₂[Cu(ecda)₂], Pd[Cu(ecda)₂] and Ag₂[Cu(ecda)₂] is the complete quenching of paramagnetism showing the presence of strongly antiferromagnetically coupled copper(II) centres at room temperature. Temperature dependent compressed pellet conductivities of the complexes have been determined in the temperature range 303–373 K. All the complexes exhibited σ_rt in 10⁻¹¹–10⁻⁷ S cm⁻¹ range. The complexes [n-Bu₄N]₂[Cu(ecda)₂], [Fe(phen)₃]-[Cu(ecda)₂], Pd[Cu(ecda)₂] and Ag₂[Cu(ecda)₂] are semiconductors as their conductivity increases with the increase in temperature, with E_a=0.03–4.70 eV.     

The first BDH-TTP radical cation salts with mercuric counterions, κ-(BDH-TTP)4[Hg(SCN)4]·C6H5NO2 and α′-(BDH-TTP)6[Hg(SCN)3][Hg(SCN)4]

Two new radical cation salts of the non-TTF containing donor BDH-TTP with the thiocyanatomercurate anions were synthesized. The κ-(BDH-TTP)₄[Hg(SCN)₄]·C₆H₅NO₂ (1) and α′-(BDH-TTP)₆[Hg(SCN)₃][Hg(SCN)₄] (2) salts were characterized by single crystal X-ray diffraction, electrical resistance measurements and electronic band structure calculations. Both salts have a layered structure in which the BDH-TTP layers of κ- or α′-type alternate with anionic sheets. The anionic layers of 1 contain the counterion [Hg(SCN)₄]²⁻ and the nitrobenzene molecule which are statistically disordered. Salt 2 contains two different layers (although both of the α′-type) of the organic donors, a somewhat unusual fact in organic conductors. The anion layers of 2 consist of polymeric chains built up from a combination of the two different anions, [Hg(SCN)₃]¹⁻ and [Hg(SCN)₄]²⁻. Salt 1 shows a metallic behavior down to helium temperatures whereas salt 2 exhibits two-phase transitions in the temperature range 295–8 K.     

Spectroscopic studies of the radical cation salt (BEDT-TTF)2Pt(NO2)4

We report on spectroscopic studies of the charge transfer salt formed by the organic donor bis(ethelenedithio)tetrathiafulvalene (BEDT-TTF) and [Pt(NO₂)₄]²⁻ anions. In this salt BEDT-TTF molecules are arranged in well-isolated (BEDT-TTF⁺)₂ dimers. Polarized reflectance spectra of single crystals were measured in the IR region (650–6500 cm⁻¹). Moreover, absorption spectra (400–15,000 cm⁻¹) and FT-NIR Raman spectra of powdered crystals dispersed in KBr pellets were recorded. Vibrational and electronic features are discussed. We suggest that the frequency of the CC stretching ν₃(a_g) mode depends non-linearly on the degree of ionization of BEDT-TTF.     

Mass-balance and Eh-pH diagrams of Fe green rust in aqueous sulphated solution

The properties of a Fe^II-Fe^III mass-balance diagram are presented. Each compound is represented by a point P(x, R), where x=n_Fe^III/[n_Fe^II+n_Fe^III] is the ferric molar fraction and R=n_OH^-/[n_Fe^II+n_Fe^III] the number of mole of hydroxyl species necessary to precipitate one mole of iron in a given compound. If a chemical reaction leads to a given point P(x, R) in the diagram, the nature and relative abundance of the various iron species can be predicted by using simple rules that resemble those commonly used when studying binary and ternary phase diagrams. Reactions of oxidation of Fe^II species or coprecipitation reactions of Fe^II and Fe^III species are represented by different routes in the diagram. The evolution of the measured pH and redox potential E_h values during a controlled Fe^II oxidation experiment using sodium persulphate is explained by comparing the mass-balance and the E_h-pH Pourbaix diagrams. These values are also measured at the intersecting points of various routes and identical equilibrium conditions are often obtained. By displaying the involved chemical reactions, the Fe^II-Fe^III mass-balance diagram allows to understand the reaction path consequently followed in the E_h-pH Pourbaix diagram.     

New BETS salt with the square planar [Ni(CN)4]2− anion

The new radical cation salt based on bis(ethylenedithio)tetraselenafulvalene (BETS) with the square planar [Ni(CN)₄]²⁻ anion was synthesized by electrocrystallization: (BETS)₄·Ni(CN)₄. X-ray analysis, electron transport, magnetotransport and electronic band structure calculations are presented and discussed.     

Vibrational spectra of β″-(ET)3X2 (X = HSO4, ClO4) salts

The IR and Raman spectra of β″-(ET)₃X₂ [X = HSO₄ and ClO₄] salts were measured at various temperatures below 300 K. The ν₂ and ν₂₇ modes exhibit the splitting into two peaks below the metal–insulator transition temperature. This phenomenon is ascribed to the charge ordered (CO) state. The CO patterns of the presented compounds were determined on the basis of the numerical calculation of the vibronic ν_3L mode. The assignment of the ν₂₇ mode of ET⁺ was confirmed through the measurement of the reflectance spectra of the 1:1 salts (ET)ClO₄, (ET)AuCl₂Br₂ and the isotope analogues. The ν₂₇ mode is the efficient probe to the site charges of the ET salts.     

Synthesis and crystal structure of an organic-inorganic complex [Cu（DMF）3（H2O）2]2[SiMo12O40]·2H2O

The synthesis and crystal smacture of an polyoxometalate-based organic-inorganic complex [Cu（DMF）3（H2O）212[SiMo12O40].2H2O （DMF = N, N-dimethyl formamide） is described in this article. It was characterized using elemental analysis, thermal analysis, infrared, ultraviolet, and electron spin resonance spectroscopic studies. The X-ray crystallography analysis showed that the copper centers are pentacoordinated to show the square pyramidal geometry, and the polyanion [SiMo12O40]4- which is semi-coordinated to the copper（I/） centers prevents the existence of a sixth ligand. In addition, the intracationic hydrogen interaction enhanced the stability of the copper coordination cation.     

Coordination polymers with [Au(CN)4]- building blocks: a 1-d chain of molecular NiII2AuIII2 squares

A new coordination polymer utilizing the neglected cyanoaurate anion [Au(CN)₄]- building block is reported. Reaction of a Ni(II) salt, diethylenediamine (dien) and K[Au(CN)₄] yields Ni(dien)[Au(CN)4]₂, which consists of a unique bimetallic Ni(II)₂/Au(III)₂ supramolecular square through cis N(cyano) bridging of the [Au(CN)₄]- building block to [Ni(dien)]²⁺ cations. These squares further aggregate into a 1-D chain via Au-N(cyano) interactions; no Au(III)-Au(III) interactions are observed. Within the square, the magnetic coupling between the Ni(II) centres is very weak, indicating that the [Au(CN)₄]- unit is a poor mediator of magnetic exchange in this system.     

Low-dimensional magnetic behaviour of new radical-ion salts: (BEDT-TTF)2[AuIII(i-mnt)2] and (BEDT-TTF)2[BiBr4]

Electrical and magnetic properties of two new radicalion salts of BEDT-TTF (BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene) are reported. (BEDT-TTF)₂[Au^III(i-mnt)₂] (i-mnt is 1,1-dithio-2,2-dicyano-ethylene) is a semiconductor, σ_r.t. = 2.0 × 10⁻¹−5.5 × 10⁻² S cm⁻¹ with a temperature dependent activation energy (0.14–19 eV). The powder magnetic susceptibility (10–300 K) has been fitted according to a uniform antiferromagnetic (S = 1/2) Heisenberg model by using the experimental g value of 2.0067 and a magnetic exchange constant J/k_B of −110 K. (BEDT-TTF)₂ [BiBr₄] shows similar electrical and magnetic behaviour with σ_r.t. = 5 × 10⁻² S cm⁻¹ on a powdered sample and J/k_B = − 79 K. At low temperature impurities are responsible for the Curie-like behaviour.     

Crystal structure,ESR and conductivity studies of bis(ethylenedithio)tetrathiafulvalene (ET) organic conductor (H8-ET)2[Hg(SCN)2Br] and its deuterated analogue (D8-ET)2[Hg(SCN)2Br]

Protonated (I) and deuterated (II) crystals of (ET)₂[Hg(SCN)₂Br] (ET = bis(ethylenedithio)tetrathiafulvalene) are isostructural with B2/b space group and Z = 4. Crystal structure consists of (ET)₂⁺ dimers forming a κ-type motif and arranged in layers parallel to the bc-plane which are separated by anionic sheets of polymeric anions. A two-positional disorder exists in ethylene groups of deuterated ET molecules, while such disorder appears only in one of the ethylene groups in the hydrogenated salt. The crystals exhibit semimetallic behaviour at high temperatures with a transition to non-metallic state at 100 K for salt I and 60 K for salt II as is shown from d.c. conductivity measurements. Electron spin resonance (ESR) g factor and linewidth and their temperature behaviour are extensively discussed on the basis of existing theories and experimental data for low-dimensional organic conductors. The linewidth is determined by spin-phonon scattering driven relaxation processes which are mediated by Peierls fluctuations in the conducting phase and by spin-lattice relaxation processes below the critical temperature. The first-order phase transition in hydrogenated salt at 100 K is associated with a localization of electrons on ET dimers, whereas the transition of semiconductor-semiconductor type with possible magnetic ordering is suggested for deuterated salt. A considerable isotope effect in (ET)₂[Hg(SCN)₂Br] is considered to be related to a weak hydrogen bond between the terminal ethylene group of ET^dot;+ and the bromine atom of the anion in hydrogenated salt. A discussion of the nature of the phase transitions is given.     

Gold complexes with

The reactions of methane with the gold complexes [Au(OH)]⁻, [Au(OCH₃)₄]⁻, [Au(O(CO)₂O₂]⁻ and [Au(O₂CH)₂]⁺, [Au^I(acac)], [Au^III(acac)₂]⁺ (acac-acetylacetonato) were studied using the DFT/PBE method with the SBK basis set. High activation barriers were obtained for the electrophilic substitution in [Au(OH)]⁻, [Au(OCH₃)⁴]⁻, [Au(O(CO)₂O)₂]-and [Au^III(acac)₂]⁺ complexes, which excludes the possibility that these reactions might proceed under mild conditions. The reactions of the [Au(HCO₂)₂]⁺ and [AuI(acac)] complexes with methane have rather low energy barriers and proceed through the formation of an intermediate complex. The alternative mechanism of methane oxidation with a gold complex in the presence of oxygen is simulated.     

Synthesis and crystal structure and nonlinear optical properties of polymeric W （Mo）-Cu-S cluster

The polymeric chalcogenide [W2O2S6Cu4（NCMe）4]n （compound 1） was synthesized by the self-assembly reaction of （NHa）2（WOS3） with CuBr in MeCN in the presence of tricyclohexylphosphane （PCy3） under a purified nitrogen atmosphere using standard Schlenk techniques. It gives rise to a novel ID polymeric compound 1 with solvent MeCN coordinated to the copper atom. This situation is unprecedented in the W（Mo）/Cu/S system. The crystals were characterized by elemental analysis, IR and single-crystal X-ray crystallography. The configuration of the polymeric compound can be viewed as a helical chain which is propagated along the crystallographic c axis. The excited state absorption and refraction of compound 1 in CH3CN solution were studied by using the Z-scan technique with laser pulses of 40 ps pulse-width at a wavelength of 532 nm. The polymeric compound possesses an optical self-focusing performance. The positive nonlinear refraction is attributed to population transitions between singlet states. Compound 1 displays a strong excited-state absorption.     

Formation of ‘ferric green rust’ and/or ferrihydrite by fast oxidation of iron(II-III) hydroxychloride green rust

Fast oxidation processes of iron(II-III) hydroxychloride green rust GR(Cl⁻), Fe^II₃Fe^III(OH)₈Cl · 2H₂O, were simulated by two different methods. The first one consisted in using a strong oxidiser, namely H₂O₂. The main end product, analysed by X-ray diffraction and Mössbauer spectroscopy, is an iron(III) compound, designated as “ferric GR(Cl⁻)”, characterised by a layered structure identical to that of normal GR(Cl⁻). The second method consisted in decreasing the initial concentrations of reactants, thus increasing the proportion of dissolved O₂. Suspensions of GR(Cl⁻), obtained by mixing 4 × 10⁻³ M NaOH with FeCl₂ solutions for various R^′=[Cl⁻]/[OH⁻] values, oxidised rapidly into ferrihydrite-like compounds.