Silica-[Fe(bpy)3] composite particles with photo-responsive change of color and magnetic property

Photo-induced complex formation of tris-2,2′-bipyridine iron(II) complex ([Fe(bpy)₃]²⁺) from the mixture of FeCl₃ and 2,2′-bipyridine was achieved in silica gel containing 150-300 μm silica particles, derived from a complex emulsion with HCl aqueous solution and tetraethyl orthosilicate (TEOS). More than 95% of Fe(III) and 2,2′-bipyridine were incorporated in silica particles. Yellow-red color change, due to [Fe(bpy)₃]²⁺, was observed by irradiation with 365 nm UV beam at 0.3 mW cm⁻² for 120 s. The complex formation accompanies simultaneous spin transition from the high-spin state of Fe(III) to the low-spin state of Fe(II).     

Magnetic Susceptibility in Normal States of Quasi-One-Dimensional Superconductors

The longitudinal magnetoresistance of a two-dimensional superconductor, β’-Et₂Me₂P[Pd(dmit)₂]₂ (dmit=C₃S ₅ ²⁻ ) under hydrostatic pressure was measured at low temperatures with the field applied perpendicular to the conducting layers. At 0.58 GPa, the field-dependent isothermal interlayer resistanceR╧ (H) exhibited a peak below the superconducting transition temperature T _C . This peak effect can be explained by a model of resistively-shunted Josephson-Junctions. The peak is strongly suppressed at a higher pressure, 0.71 GPa.     

Locking and Unlocking the Molecular Spin Crossover Transition

The Fe(II) spin crossover complex [Fe{H₂B(pz)₂}₂(bipy)] (pz = pyrazol‐1‐yl, bipy = 2,2′‐bipyridine) can be locked in a largely low‐spin‐state configuration over a temperature range that includes temperatures well above the thermal spin crossover temperature of 160 K. This locking of the spin state is achieved for nanometer thin films of this complex in two distinct ways: through substrate interactions with dielectric substrates such as SiO₂ and Al₂O₃, or in powder samples by mixing with the strongly dipolar zwitterionic p ‐benzoquinonemonoimine C₆H₂(—? NH₂)₂(—? O)₂. Remarkably, it is found in both cases that incident X‐ray fluences then restore the [Fe{H₂B(pz)₂}₂(bipy)] moiety to an electronic state characteristic of the high spin state at temperatures of 200 K to above room temperature; that is, well above the spin crossover transition temperature for the pristine powder, and well above the temperatures characteristic of light‐ or X‐ray‐induced excited‐spin‐state trapping. Heating slightly above room temperature allows the initial locked state to be restored. These findings, supported by theory, show how the spin crossover transition can be manipulated reversibly around room temperature by appropriate design of the electrostatic and chemical environment.     

Electrical properties of complex bimetallic salts [M(N–N)3]2+[Cu(MNT)2]2− and heterobimetallic AgI–CuII/HgII–CuII bis(maleonitriledithiolato) bridged coordination polymers

This paper presents the solid-state electrical conductance properties of a series of complex bimetallic salts of the form [M(N–N)₃][Cu(MNT)₂] (M=Fe(II), Co(II), Ni(II), or Cd(II); N–N=1,10-phenanthroline (phen) or ethylenediamine (en); MNT²⁻=maleonitriledithiolate) and bridged heterobimetallic complexes Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] that have been prepared by treatment of complex salt Na₂[Cu(MNT)₂] (generated in situ) with one equivalent of cationic complexes [M(N–N)₃]X₂ or Hg(CH₃COO)₂ and two-equivalent of AgNO₃ in aqueous–methanol mixture and characterised by relevant spectroscopies (IR, EPR, UV-Visible) as well as by powder XRD spectra. Solution conductivity measurements in 10⁻³ M DMSO solution revealed 1:1 electrolytic behaviour of the bimetallic salts. Diamagnetism together with powder EPR spectra for Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] show strong antiferromagnetic interaction between two adjacent copper(II) centers at room temperature. Majority of the complexes exhibited compressed pellet σ_rt in 8.19×10⁻¹¹ to 5.37×10⁻⁷ S cm⁻¹ range and show semiconductivity over the 303–383 K temperature range. Conductivity of both coordination polymers are appreciably higher compared to the bimetallic salts. For the salts [Co(phen)₃][Cu(MNT)₂], [Ni(phen)₃][Cu(MNT)₂] and bridged complexes Ag₂[Cu(MNT)₂] and Hg[Cu(MNT)₂] the conductivity remarkably increases, i.e., 10² to 10³ order of magnitude at elevated temperature showing some sort of phase transformation producing S⋯S intermolecular contact.     

An Approach to the Origin of Transport Properties in a Series of Molecular Conductors, Based on XPS and Spectroscopic Studies

X-ray Photoelectron Spectroscopy and Raman spectroscopy are combined to evaluate the stoichiometry and charge state of building units in conductive films containing TTF, ET or TMTSF donors and [Ni(dmit)₂] or [M(dcbdt)₂] acceptors.     

Reduction of Np(V) with Fe(II) in weakly acidic solutions containing H<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The kinetics of the reaction of Np(V) with Fe(II) in dilute perchloric and nitric acid solutions containing H₂C₂O₄ was studied by spectrophotometry. In the range pH 1–2, the reaction rate is described by the equation d[Np(V)]/dt = k[Np(V)][Fe(II)][H₂C₂O₄]²[H⁺]^−1.6, k = 182 mol^−1.4 l^1.4 s⁻¹. The activation energy in the range 25–45°C is 26 kJ mol⁻¹. The reaction mechanism involves formation of Fe(II) and Np(V) oxalate complexes, followed by their reaction with the participation of the H⁺ ion.     

Kinetics of Redox Reactions of U, Pu, and Np in TBP Solutions: VII. Kinetics of Reduction of Pu(IV) and Np(VI) with Butanal Oxime in Undiluted TBP

The kinetics of reduction of Pu(IV) and Np(VI) with butanal oxime in undiluted TBP containing HNO₃ was studied spectrophotometrically. In the range [HNO₃] = 0.08-0.75 M the rate of Pu(IV) reduction is described by the equation -d[Pu(IV)]/dt = k[Pu(IV)]²[C₃H₇CHNOH]/{[Pu(III)][HNO₃]²} with the rate constant k = 0.068±0.017 mol l^-1 min^-1 at 20°C. The kinetic equation of the reduction of Np(VI) to Np(V) in the range [HNO₃] = 0.01-0.27 M is -d[Np(VI)]/dt = k[Np(VI)][C₃H₇CHNOH][H₂O]²/[HNO₃]0.5, where k = 0.058±0.007 l2.5 mol-2.5 min^-1 at 25°C, and the activation energy is 79±9 kJ mol^-1.     

Engineering On‐Surface Spin Crossover: Spin‐State Switching in a Self‐Assembled Film of Vacuum‐Sublimable Functional Molecule

The realization of spin‐crossover (SCO)‐based applications requires study of the spin‐state switching characteristics of SCO complex molecules within nanostructured environments, especially on surfaces. Except for a very few cases, the SCO of a surface‐bound thin molecular film is either quenched or heavily altered due to: (i) molecule–surface interactions and (ii) differing intermolecular interactions in films relative to the bulk. By fabricating SCO complexes on a weakly interacting surface, the interfacial quenching problem is tackled. However, engineering intermolecular interactions in thin SCO active films is rather difficult. Here, a molecular self‐assembly strategy is proposed to fabricate thin spin‐switchable surface‐bound films with programmable intermolecular interactions. Molecular engineering of the parent complex system [Fe(H₂B(pz)₂)₂(bpy)] (pz = pyrazole, bpy = 2,2′‐bipyridine) with a dodecyl (C₁₂) alkyl chain yields a classical amphiphile‐like functional and vacuum‐sublimable charge‐neutral Fe^II complex, [Fe(H₂B(pz)₂)₂(C₁₂‐bpy)] (C₁₂‐bpy = dodecyl[2,2′‐bipyridine]‐5‐carboxylate). Both the bulk powder and 10 nm thin films sublimed onto either quartz glass or SiO_x surfaces of the complex show comparable spin‐state switching characteristics mediated by similar lamellar bilayer like self‐assembly/molecular interactions. This unprecedented observation augurs well for the development of SCO‐based applications, especially in molecular spintronics.     

Direct Visualization of Local Spin Transition Behaviors in Thin Molecular Films by Bimodal AFM

Thin films of the molecular spin‐crossover complex [Fe(HB(1,2,4‐triazol‐1‐yl)₃)₂] undergo spin transition above room temperature, which can be exploited in sensors, actuators, and information processing devices. Variable temperature viscoelastic mapping of the films by atomic force microscopy reveals a pronounced decrease of the elastic modulus when going from the low spin (5.2 ± 0.4 GPa) to the high spin (3.6 ± 0.2 GPa) state, which is also accompanied by increasing energy dissipation. This technique allows imaging, with high spatial resolution, of the formation of high spin puddles around film defects, which is ascribed to local strain relaxation. On the other hand, no clustering process due to cooperative phenomena was observed. This experimental approach sets the stage for the investigation of spin transition at the nanoscale, including phase nucleation and evolution as well as local strain effects.     

Mo&#x030B;ssbauer spectroscopy studies of polyacetylene doped with iron chloride complexes

The⁵⁷ Fe Mo&#x030B;ssbauer resonance has been applied to study polyacetylene films doped chemically and electrochemically to different doping levels. Both methods lead to the insertion of a high spin Fe^III complex with Mo&#x030B;ssbauer parameters characteristic of FeCl^?₄. Degradation of [CH(FeCl₄)_y]_x in air leads to gradual transformation of Fe^III into a high spin Fe^II.     

Variety of valence bond states formed of frustrated spins on triangular lattices based on a two-level system Pd(dmit)2

Abstract

Recent studies on the physical properties of the triangular system based on the Pd(dmit)₂ salts (dmit=1,3-dithiole-2-thione-4,5-dithiolate) are reviewed. Quantum chemical architectures of the Pd(dmit)₂ molecule and its dimer are introduced with emphasis on the strong dimerization of a two-level system, which provides unique physical properties of the salts. The magnetic properties are outlined in view of the magneto-structural correlation specific to the frustrated spin systems. Some newly discovered ground states and their origins are discussed, for which the valence bond formation plays a key role. Among them, the two-level structure is crucial for the novel charge-separated state found in two salts. The valence bond ordering, similar to the spin-Peierls transition, has been found in a two-dimensional frustrated spin system. The physical aspects and possible relation to the pressure-induced superconductivity are discussed.     

Tc(VII)-catalyzed oxidation of U(IV) with nitric acid in solution of TBP in <Emphasis Type="Italic">n</Emphasis>-dodecane

Oxidation of U(IV) with nitric acid in 30% solution of TBP in n-dodecane is catalyzed by Tc ions; the rate-determining steps are 3U(IV) + 2Tc(VII) → 3U(VI) + 2Tc(IV) and Tc(IV) + Tc(VII) → Tc(V) + Tc(VI). Oxidation of U(IV) is inhibited by the reaction product, HNO₂, which partially binds Tc(IV) ions (TcO²⁺) in an inert complex. The overall rate equation of U(IV) oxidation is-d[U(IV)]/dt = k ₁[U(IV)][Tc][HNO₃]^?3 ? k ₄[U(IV)]²[HNO₂]²[HNO₃]^?1, where k ₁ = 4.8 ± 1.0 mol²1^?2 min^?1 and k ₄ = (2.4 ± 1.0) × 10⁵ 1² mol^?2 min^?1 at 25°C, [H₂O] = 0.4 M ([Tc] is the total Tc concentration in the reaction mixture). Water and U(VI) have no effect on the reaction rate.     

Behavior of Microamounts of <Superscript>22</Superscript>Na, <Superscript>85</Superscript>Sr, <Superscript>137</Superscript>Cs,and <Superscript>152</Superscript>Eu in Sorption and Coprecipitation on Mixed Potassium Neodymium Ferrocyanide from Solutions

Sorption of ⁸⁵Sr, ¹³⁷Cs, ²²Na, and ¹⁵²Eu on solid mixed potassium neodymium ferrocyanide KNd[Fe(CN)₆]·4H₂O from neutral, acidic, and alkaline media and also coprecipitation of these radionuclides with KNd[Fe(CN)₆]·4H₂O in its formation from a homogeneous solution were studied. It was found that ⁸⁵Sr and ²²Na do not noticeably coprecipitate with solid KNd[Fe(CN)₆]·4H₂O and are not sorbed by this substance. In aqueous medium, depending on the cesium concentration in solution, from 80 to 98% of ¹³⁷Cs coprecipitates with solid KNd[Fe(CN)₆]·4H₂O. In this case, the distribution coefficient K_d depends on both the cesium concentration in solution and solution pH. Within 30 min of contact of the solid and liquid phases, the degree of recovery of ¹³⁷Cs from aqueous solution with KNd[Fe(CN)₆]·4H₂O is approximately 95.0% of the initial amount. ¹⁵²Eu coprecipitates with solid KNd[Fe(CN)₆]·4H₂O during its formation from a homogeneous solution to 98–99.9%. The degree of recovery of ¹⁵²Eu from aqueous solution with KNd[Fe(CN)₆]·4H₂O precipitate within 60 min of contact of the solid and liquid phases is 70.3% of the initial amount.     

Localization of U(VI) on nickel hydroxide from aqueous solution in the presence of complexing anions at 25°C

Sorption and coprecipitation of U(VI) from aqueous solution containing various complexing anions (CO₃^25-, SO₄²⁻, H₂EDTA²⁻) with the Ni(OH)₂ solid phase at 25°C was studied. Uranium(VI) is not noticeably sorbed on the Ni(OH)₂ solid phase from aqueous solutions containing CO₃²⁻ and SO₄²⁻. The distribution coefficients K _d are less than 1.0 ml g⁻¹ throughout the examined range of [U(VI)]: [L] ratios (L = CO₃²⁻, SO₄²⁻) at V/m ≥ 100 ml g⁻¹ and contact time of the solid and liquid phases of 60 min. In the presence and in the absence of H₂EDTA²⁻, the degree of the U(VI) sorption is essentially the same (K _d ∼90–140 ml g⁻¹ at V/m ≥ 100 ml g⁻¹). Uranium(VI) does not coprecipitate with Ni(OH)₂ from aqueous solutions containing SO₄²⁻ and H₂EDTA²⁻. The distribution coefficients K _d are less than 0.001 ml g⁻¹ at V/m ≥ 200 ml g⁻¹ and contact time of the solid and liquid phases of 60 min. In solutions containing CO₃²⁻, the U(VI) capture by the Ni(OH)₂ precipitate depends on the [CO₃²⁻]: [U(VI)] ratio. The higher the [CO₃²⁻]: [U(VI)] ratio, the more strongly U(VI) coprecipitates with Ni(OH)₂.     

Coprecipitation of 60Co from aqueous solutions with solid phases of various coordination compounds

Coprecipitation of ⁶⁰Co from aqueous solutions with solid phases of various coordination compounds was studied. Microamounts of ⁶⁰Co do not noticeably coprecipitate with solid phases of [M(CE)]BPh₄ (M = Na⁺, Cs⁺; CE = 12-crown-4, 15-crown-5, 18-crown-6) and of CsBPh₄. ⁶⁰Co can be efficiently removed from aqueous solutions containing 0.1 and 4.0 M NaNO₃, 0.1 M EDTA, or 1.0 M H₂C₂O₄ by coprecipitation with the KFe[Fe(CN)₆] solid phase formed by successive addition of K₄[Fe(CN)₆] and Fe(NO₃)₃ into these solutions. The degree of ⁶⁰Co removal varies from ～80 to ～99.9% depending on the experimental conditions. This procedure allows simultaneous removal of ¹³⁷Cs from the same solution with no less than 97% efficiency.     

Conglomerate crystallization behavior of racemic [Co(N4)(aminoacidato)]2+ complexes

Crystal structures, absolute configurations, and crystalline packing features of nine complexes, namely, cis-α-Λ-(RR)(δλδ)-[Co(trien)(D-histidinato)](ClO₄)₂·2H₂O 1, cis-β₁-Δ-(RR)(λδδ)- [Co(trien)(L-asparaginato)](ClO₄)₂ 2, cis-β₂-Λ(SS)(λλδ)-[Co(trien)(L-valinato)](ClO₄)₂·H₂O 3, cis-β₂-Δ-(RR)(δδλ)[Co(trien)(D-methioninato)](ClO₄)₂ and its enantiomer 4, trans(N,t-N)-[Co(tren)(DL-leucinato)]X₂, (X=ClO₄⁻ 5, BF₄⁻ 6, PF₆⁻ 7), and trans(N,t-N)-[Co(tren)(DL- methioninato)]X₂ (X=Br⁻ 8, Cl⁻(BF₄⁻) 9) (trien=triethylenetetramine, tren=tris(2-aminoethyl)amine), have been determined. All compounds were prepared from racemic DL-amino acid. 1–3 crystallize as conglomerates. 5–7 are isomorphous and crystallize as the so-called conglomeratic solids. While 4, 8 and 9 undergo racemic crystallization. In 1–7, the carboxylic oxygen of the amino acid forms double hydrogen bonds with the amino hydrogen atoms of N4 and/or amino acidato of an adjacent cation. By these hydrogen bonds, cations having the same chirality are linked together into helical string. In the isomorphous 8 and 9, the cation containing L-methionine interacts with a cation containing D-methioninine, through hydrogen bonds, to form a racemic pair, and no spiral string arrangements are observed.     

Atomic-level insights into the modification mechanism of Fe (III) ion on smithsonite (1 0 1) surface from DFT calculation

Fe(III) ion can strongly inhibit the sulphidation amine flotation of smithsonite. However, its modification mechanism on smithsonite surface is still obscure. In this work, a systematic study of the modification of Fe(III) ion on smithsonite (1 0 1) surface was performed using DFT calculation. The optimal number of H₂O ligands for Fe(III) ion hydrates in aqueous conditions was probed, and [Fe(OH)₂(H₂O)₄]⁺ and [Fe(OH)₄]^? were identified as the major modification species, then their adsorption and bonding mechanisms were further revealed by analyzing the frontier orbitals, density of state, Mulliken population, and electron density. The calculated adsorption structures were consistent with the former experiment, and we found the O site that bonded to the C atom on smithsonite surface was the most favorable position for [Fe(OH)₂(H₂O)₄]⁺ and [Fe(OH)₄]^? adsorptions. Besides, their adsorption mechanisms on smithsonite surface were principally due to the combined effect of FeO bond and hydrogen bonding. Simultaneously, hydrogen bonding greatly enhanced the stability of the adsorption structures. Moreover, the dominant orbital contribution for the bonding of FeO was primarily due to the orbital hybridization between Fe 3d and O 2p orbitals. This work can help in deeper understanding of the depression of Fe(III) ion on the sulphidation amine flotation of smithsonite.     

Cationic cyclometallated iridium(III) complexes with substituted 1,10-phenanthrolines: the role of the cyclometallated moiety on this new class of complexes with interesting luminescent and second order non linear optical properties

The luminescence and second order non linear optical (NLO) response of [Ir(ttpy)₂(5-R-1,10-phen)][PF₆] (ttpy = cyclometallated 3′-(2-pyridil)-2,2′:5′,2″-terthiophene, phen = phenanthroline; R = Me, NO₂) and [Ir(pq)₂(5-R-1,10-phen)][PF₆] (pq = cyclometallated 2-phenylquinoline) have been investigated experimentally in CH₂Cl₂ solution and compared with that of [Ir(ppy)₂(5-R-1,10-phen)][PF₆] (ppy = cyclometallated 2-phenylpyridine), characterized by one of the highest second order NLO response ever reported for a metal complex. Substitution of ppy with the more π-delocalized pq does not affect significantly the luminescence and NLO properties. A slightly lower NLO response and a much poorer luminescence is observed for the related complexes with ttpy. In these complexes, DFT/TDDFT calculations show that the presence of ttpy induces a significant downshift of the HOMO energy, compared to ppy and pq. The NLO response is dominated by intense MLCT excited states, which are also assigned as originating the emission.     

Magnetic and electrical properties of new inorganic complex based materials derived from bis(1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolato)metalate(II) ions

Magnetic and electrical properties of a series of new inorganic complex based materials [n-Pr₄N]₂[Pb(ecda)₂], [Et₄N]₄[Hg₂(ecda)₄] and M[M′(ecda)₂] (M=Co(II), Ni(II), Cu(II), Cd(II) or Pb(II); M′=Hg(II) or Pb(II); ecda²⁻=1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate) have been investigated using molecular spectroscopic (IR, Raman, EPR, electronic and mass) and conducting properties. Complete quenching of paramagnetism indicates strong Cu–Cu interaction in the layered polymeric array of Cu[Hg(ecda)₂] and Cu[Pb(ecda)₂] in the solid state. The ¹H NMR spectrum of Ni[Pb(ecda)₂] in DMSO-d₆ gives narrow unshifted peaks due to diamagnetic, square-planar geometry around Ni(II) and shows absence of some octahedral units (μ_eff=1.49 BM) present in the solid state of this product. While the peak broadening indicates paramagnetic nature and absence of dominant Cu–Cu interaction in solution for Cu[Hg(ecda)₂] and Cu[Pb(ecda)₂]. The temperature dependent (305–373 K) compressed pellet conductivity together with activation energy (0.36–1.23 eV), show semiconducting behaviour of some of the bimetallic derivatives.     

Transition metal ferrocenyl dithiocarbamates functionalized dye-sensitized solar cells with hydroxy as an anchoring group

Three new transition-metal dithiocarbamates involving ferrocene (Fc), namely [Co(FcCH₂EtOHdtc)₃] (Co), [M(FcCH₂EtOHdtc)₂] M = Ni (Ni), Cu (Cu) (EtOHdtc = N-ethanol dithiocarbamate), have been synthesized and characterized by microanalyses, FTIR, ¹H and ¹³C NMR spectroscopies and single crystal X-ray diffraction technique. The peak broadening in the ¹H spectrum of the copper complex indicates the paramagnetic behavior of this compound. The observed single quasi-reversible cyclic voltammograms for the complexes indicate the stabilization of a metal center (except copper) other than Fe in their characteristic oxidation state. These complexes have been used as photo-sensitizer in dye-sensitized solar cells which indicates that Co displays the best photosensitization property with an overall conversion efficiency of 3.25 ± 0.04%. The low cell efficiency of Ni and Cu complexes may be due to slow regeneration of the dye by iodine/iodide redox couple followed by charge injection into TiO₂.