Reversible photomagnetic properties of the molecular compound [{Cu(bipy)2}2{Mo(CN)8}]·9H2O·CH3OH

The optical and photomagnetic properties of [{Cu^II(bipy)₂}₂{Mo^IV(CN)₈}]·9H₂O·CH₃OH (1) have been reinvestigated. A comparison between spectra in solution and in the solid state revealed the presence of an intervalence band (or Metal–Metal Charge Transfer, hereafter noted MMCT) at 570 nm. The photomagnetic properties have been performed in a Superconducting QUantum Interference Device at 10 K with irradiation in the range of the MMCT: 488 nm, 520 nm and 647 nm at 10 K. An important increase of the magnetic signal has been measured after 1 h of irradiation at 488 nm, whereas a weaker increase has been obtained for the irradiation at 520 nm in the same conditions. Moreover, after an excitation at 488 nm, an irradiation at 647 nm has induced a decrease of the magnetic moment, which corresponds to a partial deexcitation. The complete characterization of the photoproduct has been realised after an irradiation of 4 h at 488 nm. The photomagnetic properties have shown an increase of the paramagnetism of 1 at low temperature. After a thermal heating at 300 K, the material goes back to its initial state before irradiation. It is the first time that a fully reversible photomagnetic behaviour for the compound [{Cu^II(bipy)₂}₂{Mo^IV(CN)₈}]·9H₂O·CH₃OH has been described. The observed properties have been discussed in terms of an electron transfer mechanism Mo → Cu.     

Photoacoustic spectra of Nd(TFA)3 · 2H2O and Nd(HFA)3 · 2H2O

A new synthesis of trisfluoroacetylactone (TFA) and hexafluoroacetylactone (HFA) Nd complexes: Nd(TFA)₃ · 2H₂O and Hd(HFA)₃ · 2H₂O is reported. The photoacoustic (PA) spectra in the 300–800 nm region of the compounds NdCl₃ · 6H₂O, Nd(TFA)₃ · 2H₂O and Nd(HFA)₃ · 2H₂O are reported. The PA absorption bands are assigned and their relative intensities represented by intensity branching vectors are calculated. The perturbation of the ligand on the energy levels of Nd³⁺ ion is discussed and a model of the relaxation process of Nd(HFA)₃ · 2H₂O is proposed based on its PA and absorption spectra.     

Electrochemical, spectroelectrochemical and theoretical studies on the reduction and deprotonation of the photovoltaic sensitizer [(H3-tctpy)Ru(NCS)3] (H3-tctpy=2,2′:6′,2′′-terpyridine-4,4′,4′′-tricarboxylic acid)

The electrochemical reduction of the black dye photosensitizer [(H₃-tctpy)Ru^II(NCS)₃]⁻ (H₃-tctpy=2,2′:6′,2′′-terpyridine-4,4′,4′′-tricarboxylic acid) used in photovoltaic cells has been found to be a complex process when studied in dimethylformamide. At low temperatures, fast scan rates and at a glassy carbon electrode, the chemically reversible ligand based one-electron reduction process [(H₃-tctpy)Ru(NCS)₃]⁻+e⁻[(H₃-tctpy√⁻)Ru(NCS)₃]²⁻ is detected. This process has a reversible half-wave potential (E^r_1/2) of −1585±20 mV versus Fc/Fc⁺ at 25°C. Under other conditions, a deprotonation reaction occurs upon reduction, which produces [(H_3−x-tctpy^x−)Ru(NCS)₃]^(1+x)− and hydrogen gas. Mechanistic pathways giving rise to the final products are discussed. The E^r_1/2-value for the ligand based reductions of the deprotonated complex is 0.70 V more negative than for [(H₃-tctpy)Ru(NCS)₃]⁻. Consequently, data obtained from molecular orbital calculations are consistent with the reaction [(H₃-tctpy)Ru(NCS)₃]⁻+e⁻→[(H₂-tctpy⁻)Ru(NCS)₃]²⁻+1/2H₂ yielding the monodeprotonated complex as the major product obtained after electrochemical reduction of [(H₃-tctpy)Ru(NCS)₃]⁻. The E^r_1/2-values for the metal based Ru^II/III process differ by 0.30 V when data obtained for the protonated and deprotonated forms of the black dye are compared. Electronic spectra obtained during the course of experiments in an optically transparent thin layer electrolysis configuration are consistent with the overall reaction scheme proposed on the basis of voltammetric measurements and molecular orbital calculations. Reduction studies on the free ligand, H₃-tcpy, are consistent with results obtained with [(H₃-tctpy)Ru(NCS)₃]⁻.     

IR and Raman spectra of two layered aluminium phosphates Co(en)3Al3P4O16 · 3H2O and [NH4]3[Co(NH3)6]3[Al2(PO4)4]2 · 2H2O

The FT IR and FT Raman spectra of Co(en)₃Al₃P₄O₁₆ · 3H₂O (compound I) and [NH₄]₃[Co(NH₃)₆]₃[Al₂(PO₄)₄]₂ · 2H₂O (compound II) are recorded and analysed based on the vibrations of Co(en)₃³⁺, Co(NH₃)₆³⁺, NH₄⁺, Al---O---P, PO₃, PO₂ and H₂O. The observed splitting of bands indicate that the site symmetry and correlation field effects are appreciable in both the compounds. In compound I, the overtone of CH₂ deformation Fermi resonates with its symmetric stretching vibration. The NH₄ ion in compound II is not free to rotate in the crystalline lattice. Hydrogen bonding of different groups is also discussed.     

Vibrational spectra of α-Ge(HPO4)2·H2O compound

We have measured Raman and infrared spectra of α-Ge(HPO₄)₂·H₂O compound at room temperature. The analysis of vibrational modes indicated the presence of two non-equivalent HPO₄²⁻ units in agreement with ³¹P nuclear magnetic resonance measurements. A tentative assignment of all the observed modes is proposed based on the previous works reported for other hydrogenphosphate-based compounds.     

Electrochemical behaviour of [Ru(L)(CO)2Cl2] [Ru(L)(CO)Cl3][Me4N] and [Ru(L)(CO)2(CH3CN)2][CF3SO3]2 complexes (L = 2,2′- bipyridine or 4,4′-isopropoxycarbonyl-2,2′-bipyridine)

The clectrochemical behaviour of the complexes [Ru^II(L)(CO)₂Cl₂], [Ru^II(L)(CO)Cl₃][Me₄N] and [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ (L = 2,2′-bipyridine or 4,4′-isopropoxycarbonyl-2,2′-bipyridine) has been investigated in CH₃CN. The oxidation of [Ru(L)(CO)₂Cl₂] produces new complexes [Ru^III(L)(CO)(CH₃CN)₂Cl]²⁺ as a consequence of the instability of the electrogenerated transient Ru^III species [Ru^III(L)(CO)₂Cl₂]⁺. In contrast, the oxidation of [Ru^II(L)(CO)Cl₃][Me₄N] produces the stable [Ru^III(L)(CO)Cl₃] complex. In contrast [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ is not oxidized in the range up to the most positive potentials achievable. The reduction of [Ru^II(L)(CO)₂Cl₂] and [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ results in the formation of identical dark blue strongly adherent electroactive films. These films exhibit the characteristics of a metal-metal bond dimer structure. No films are obtained on reduction of [Ru^II(L)(CO)Cl₃][Me₄N]. The effect of the substitution of the bipyridine ligand by electron-withdrawing carboxy ester groups on the electrochemical behaviour of all these complexes has also been investigated.     

Cation → anion energy transfer in [Cr(en)3][Cr(CN)6]·2H2O

Energy transfer from Cr(en)₃³⁺ to Cr(CN)₆³⁻ has been observed in [Cr(en)₃][Cr(CN)₆]·2H₂O with an efficiency close to unity. The ⁴T₂ & rt arrow-wavy; ²E intersystem crossing efficiency in Cr(en)₃³⁺ is also unity.     

Single-crystal characterization of Co7(OH)6(H2O)3(C4H4O4)47H2O; A new cobalt succinate identified through high-throughput synthesis

A new form of cobalt succinate has been discovered using high-throughput methods and its structure was solved by single crystal X-ray diffraction. Co₇(C₄H₄O₄)₄(OH)₆(H₂O)₃7H₂O crystallizes in the monoclinic space group P2₁/c with cell parameters: a=7.888(2) Å, b=19.082(6) Å, c=23.630(7) Å, β=91.700(5)°, V=3555(2) Å³, R₁=0.0469. This complex structure, containing 55 crystallographically distinct non-hydrogen atoms, is compared to the previously reported nickel phase, characterized using ab initio structure solution from synchrotron powder diffraction data.     

(Croconato‐κ2O,O′)bis­(1,10‐phenanthroline‐κ2N,N′)cobalt(II), and the nickel(II) and copper(II) analogues

The title complexes, [M(C₅O₅)(C₁₂H₈N₂)₂], with M = Co^II, Ni^II and Cu^II, all lie across twofold rotation axes, around which two 1,10‐phenanthroline ligands are arranged in a chiral propeller manner. The Co^II and Ni^II complexes are isostructural, with octa­hedral coordination geometry, while the local geometry of the Cu^II complex is severely distorted from octa­hedral.     

A novel 2D layer structure constructed from sandwich-type transition metal substituted tungstates and nickel coordination fragments: {[Ni(enMe)2]2[Ni(enMe)2(H2O)]2[As2W18Ni4(enMe)2O68]}·2H3O·2H2O

A novel polyoxometalate {[Ni(enMe)₂]₂[Ni(enMe)₂(H₂O)]₂[As₂W₁₈Ni₄(enMe)₂O₆₈]}·2H₃O·2H₂O (1) (enMe = 1,2-propylenediamine) has been synthesized and characterized, which is the first high-dimensional structure constructed from sandwich-type transition metal substituted tungstates and transition metal coordination groups.     

Polarized emission from Ba[Pt(CN)4]·4H2O single crystals under high pressure

The emission spectra of single crystal Ba[Pt(CN)₄]·4H₂O were measured from 0 to 23 kbar for the two electronic transitions which are polarized with Ec and E;c. They exhibit a red-shift of −280 cm⁻¹/kbar and −195 cm⁻¹/kbar, respectively. 3he red-shift is explained by a pressure induced reduction of the intermolecular separation R in the direction of the linear chain (c-axis). The emission energies obtained at different pressures are compared with the results under normal conditions for various Me[Pt(CN)₄]·xH₂O salts (with different R). The close analogy between these two methods of R-reduction supports the importance of one-dimensional interaction for the interpretation of electronic properties of the tetracyano-platinates. Ba[Pt(CN)₄]·4H₂O shows a structural transition region in the pressure range studied here.     

A linear Cu-Gd-Cu-Gd complex derived from the assembly reaction of [NaCuH3L] and [Gd(thd)3(H2O)2] (H3L = meso-1,2-diphenyl-1-(2-oxybenzamido)-2-(2-oxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetra-methyl-3,5-heptanedione)

A linear tetranuclear Cu^II-Gd^III-Cu^II-Gd^III complex [Cu^IIL^dpen(meso)Gd^III(thd)₂(H₂O)]₂ was synthesized from the reaction of [NaCu^IIL^dpen(meso)(DMF)] with [Gd^III(thd)₃(H₂O)₂], and the structures and magnetic properties were investigated, where H₃L^dpen(meso) = meso-1,2-diphenyl-1-(2-hydroxybenzamido)-2-(2-hydroxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione. The Cu^II complex component [NaCu^IIL^dpen(meso)(DMF)] has a one-dimensional (1D) chain structure, in which the Na⁺ ion is coordinated by two phenoxo and an ethoxy oxygen atoms of a Cu^II complex and an amido oxygen atom of the adjacent Cu^II unit to produce the 1D structure, in which the diphenylethylenediamine moieties have the array of {(1R,2S)-Na-(1S,2R)}_1∞. The assembly reaction of the Cu^II and Gd^III components gave a linear complex with the array of Cu(1)-Gd(1)-Cu(2)-Gd(2), in which two diphenylethylenediamine moieties have the same chirality of (1R,2S)-(1R,2S) or (1S,2R)-(1S,2R). Two linear Cu(1)-Gd(1)-Cu(2)-Gd(2) units are linked by hydrogen bonds through two water molecules to give a cyclic structure with a center of symmetry. The temperature dependence of the magnetic susceptibilities and field-dependent magnetization revealed the ferromagnetic interaction between the Cu^II and Gd^III ions within the linear chain.     

An easy electrochemical procedure for tailoring thin films containing the [Fe(bpy)2(CH3CN)2] and/or [Fe(bpy)3]-like cores (bpy=2,2-bipyridine). Application to the design of a modified electrode with a supramolecular structure

A simple electrochemical procedure to tailor thin polymeric films containing the [Fe^II(bpy)₂(CH₃CN)₂]²⁺ and/or [Fe^II(bpy)₃]²⁺-like cores have been described (bpy=2,2^′-bipyridine). The procedure is based on the electroreductive precipitation of soluble polymers prepared in situ in CH₃CN by mixing Fe³⁺ ions and a bis bipyridyl ligand, (chiragen: chir). In the resulting [Fe^II(chir)(CH₃CN)₂]_n²⁺ films, the two labile S ligands can be easily replaced by a bidentate ligand. This method has been applied with success to design a modified electrode with a supramolecular structure.     

Calorimetric measurements of diluted spin crossover complexes [FexM1−x(btr)2(NCS)2]·H2O with M = Zn and Ni

Motivated by the application of the First Order Reversal Curve (FORC) technique to obtain a distribution of like spin domains in the spin crossover complexes [Fe_xM_1−x(btr)₂(NCS)₂]·H₂O with M^II = Zn and Ni, we have performed Differential Scanning Calorimetry (DSC) experiments. We have measured the heat capacity in the heating and cooling modes and then calculated the enthalpy and the entropy variations at the phase transition. In the framework of an Ising-like model, we have converted the experimental thermal hysteresis into terms of physical parameters related to these compounds. We have also performed a statistical analysis of these parameters and concluded that the correlation between them increases with the dilution degree of these spin crossover complexes.     

Novel M(II)–Hg(II) coordination polymers generated from metal-containing building blocks M(2-pyrazinecarboxylate)2 · (H2O)2 (M=Cu, Ni, Co) and HgCl2

A new class of M(II)–Hg(II) (M=Cu(II), Co(II), Ni(II)) mixed-metal coordination polymers, Cu(2-pyrazinecarboxylate)₂HgCl₂ (4), [Co(2-pyrazinecarboxylate)₂(HgCl₂)₂] · 0.61H₂O (5) and [Ni(2-pyrazinecarboxylate)₂(HgCl₂)₂] · 0.77H₂O (6), have been prepared by self assembly of metal-containing building blocks, M(2-pyrazinecarboxylate)₂ · (H₂O)₂(M=Cu(II), Co(II), Ni(II)), with HgCl₂. Compounds 4–6 were characterized fully by IR, elemental analysis and single crystal X-ray diffraction. Compound 4 crystallized in the monoclinic space group C2/c, with a=17.916(5) Å, b=7.223(2) Å, c=13.335(4) Å, β=128.726(3)°, V=1346.2(6) ų, Z=4. It contains alternating Hg(II) and Cu(II) metal centers that are cross-linked by 2-pyrazinecarboxylate spacers and chlorine co-ligands to generate a unique three-dimensional Hg(II)–Cu(II) mixed metal framework. Compound 5 crystallized in the triclinic space group P , with a=6.3879(7) Å, b=6.6626(8) Å, c=13.2286(15) Å, α=96.339(2)°, β=91.590(2)°, γ=113.462(2)°, V=511.71(10) ų, Z=1. Compound 6 also crystallized in the triclinic space group P , with a=6.3543(8) Å, b=6.6194(8) Å, c=13.2801(16) Å, α=96.449(2)°, β=92.263(2)°, γ=113.541(2)°, V=506.67(11) ų, Z=1. Compounds 5 and 6 are isostructural and in the solid state the Hg(II)M(II)Hg(II) units are connected by Hg₂Cl₂ linkages to produce a novel M(II)–Hg(II) (M=Co(II), Ni(II)) zigzag mixed-metal chain, in which a new type of M–M′–M′–M array was observed. The metal containing building blocks, M(2-pyrazinecarboxylate)₂ · (H₂O)₂ (M=Cu(II), Co(II), Ni(II)), exhibit different connectivities to HgCl₂ depending on the metal cation contained within them.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Metal(II)-promoted hydrolysis of pyridine-2-carbonitrile to pyridine-2-carboxylic acid. The structure of [Cu(pyridine-2-carboxylate)2] · 2H2O

Pyridine-2-carbonitrile (2-CNpy) undergoes Cu(II) or Co(II)-promoted hydrolysis to pyridine-2-carboxamide (piaH) and/or pyridine-2-carboxylic acid (pycH). The pathway of pycH formation depends on the presence of 2-amino-2-hydroxymethyl-1,3-propanediol (AL¹) and on the central atom. In the absence of AL¹, Co(II) or Cu(II) ions mediate piaH formation under mild reaction conditions in the first hydrolytic step. Cu(II) ions assist in piaH transformation to pycH by subsequent reflux. In the presence of AL¹ and Co(II), a Co(II) complex containing pyoxaL¹ (2-(2-pyridinyl)-4,4-bis(hydroxymethyl)-2-oxazoline) is formed in the first stage; subsequent decomposition of pyoxaL¹ under the reflux yields pycH. Under similar conditions, no solid Cu(II) complex with pyoxaL¹ can be isolated, but a Cu(II) complex with coordinated pyc⁻ anions precipitates from the reaction mixture. The synthesis, spectral and magnetic properties of the complexes [Co(H₂O)₂ (piaH)₂]Cl₂, [Co(H₂O)₂(pyc)₂] · 2H₂O, [Cu(H₂O)₂(piaH)₂]Cl₂, [Cu(pyc)₂] and [Cu(pyc)₂] · 2H₂O, including the structure determination of the latter one, are described.     

[H3tren] templated iron fluorides; synthesis, crystal structures and Mössbauer studies

The hydrothermal synthesis, using tris-(2-ethylamino)amine (tren) as a template, and the crystal structures of three new hybrid iron fluorides, (H₃O)₂·[H₃tren]₂·(FeF₆)₂·(FeF₅(H₂O))·2H₂O (I), [H₃tren]₂·(FeF₆)₂·(FeF₂(H₂O)₄)·8H₂O (II) and [H₃tren]₂·(FeF₆)·(F)₃·H₂O (III), are reported. I, II, and III are triclinic (P-1), monoclinic (P2₁/c) and orthorhombic (I222), respectively. The structure of I is built up from isolated FeF₆ and FeF₅(H₂O) distorted octahedra separated by triprotonated [H₃tren]³⁺ cations, disordered H₃O⁺ cations and H₂O molecules. In II, Fe^IIIF₆ and neutral [Fe^IIF₂(H₂O)₄] octahedra form, together with [H₃tren]³⁺ cations, infinite (100) layers separated by extra water molecules. The structure of III consists of isolated and disordered FeF₆ octahedra, fluoride anions F⁻ connected to [H₃tren]³⁺ cations and extra fluoride anions F⁻ disordered with H₂O molecules. All [H₃tren]³⁺ cations have a “spider” type conformation. ⁵⁷Fe Mössbauer characterization shows that +III valence state can only be considered for iron cations in I and III and preliminary Mössbauer results are consistent with the presence of both +II and +III valences for iron cations in II, in agreement with the crystallographic results.     

Synthesis, crystal structure and magnetic properties of oxo-bridged binuclear iron(III) complex [Fe(phen)2PhCOO]2OCl2·7H2O

An oxo-bridged binuclear iron(III) complex, [Fe(phen)₂PhCOO]₂OCl₂·7H₂O, was synthesized and the crystal structure indicated that two octahedrally coordinated iron(III) ions bridged with oxygen atoms formed a non-linear complex. The bond angle of Fe---O---Fe is 155.6°. The studies of magnetic properties showed that there was strong antiferromagnetic superexchange coupling (J = −80.8 cm⁻) between two S = 5/2 iron(III) ions.     

Hydrothermal syntheses, crystal structures of three new organic–inorganic hybrids constructed from Keggin-type [BW12O40] clusters and transition metal complexes

Three new organic–inorganic hybrid compounds constructed from Keggin-type polyanions and transition metal complexes, [Mn(2,2′-bipy)₃]_1.5[BW₁₂O₄₀Mn(2,2′-bipy)₂(H₂O)]·0.25H₂O (1), [Fe(2,2′-bipy)₃]_1.5[BW₁₂O₄₀Fe(2,2′-bipy)₂(H₂O)]·0.5H₂O (2) and [Cu₂(phen)₂(OH)₂]₂H[Cu(H₂O)₂{BW₁₂O₄₀Cu_0.75(phen)(H₂O)}₂]·1.5H₂O (3), have been hydrothermally synthesized and characterized by elemental analyses, IR, TGA and single-crystal X-ray diffraction. Compounds 1 and 2 are isostructural and both exhibit monosupporting polyoxometalate cluster structure, each of which contains a [BW₁₂O₄₀]⁵⁻ cluster decorated by one transition metal complex. Compound 3 contains a bisupporting polyoxometalate cluster anion where two {Cu_0.75(phen)(H₂O)}^0.75+ fragments are supported on the polyoxometalate dimer {Cu(H₂O)₂(BW₁₂O₄₀)₂}⁸⁻, this represents the first bisupporting polyoxometalate cluster based on a Keggin-type polyoxometalate dimer, which are further packed together via π–π stacking contacts into an extended 1-D chain.