SPIN-CROSSOVER OF [Fe(Cl-BZIMPY)2](ClO4)2 INDUCED BY DEPROTONATION

Abstract

The ligand 4-Cl-2,6-bis(benzimidazol-2′-yl)-pyridine(Cl-bzimpy;H₂L) acts as a bidentate when coordinated with transition metal ions and the complex [Fe(Cl-bzimpy)₂](ClO₄)₂ was isolated as a solid. The protonation constants (logK). The free ligand and the complex were evaluated in 30:70 (v/v) H₂O:EtOH at room temperature and ionic strength of 0.13M (KCl). Coordination of the ligand to the metal ion leads to an increase of the acidity of the imino-hydrogen of the benzimidazole group. Deprotonation leads to a change in the spin-state (to the low-spin state; HS → LS transition) of the complex associated with a decrease in the spin-crossover equilibrium constant (K_sc). An opposite shift of spin-state is observed when HClO₄ is added to the complex solution, thus showing the reversibility of the process.     

稀土钬及铒钇丙氨酸配合物的量热与热分析研究

合成了两种固态稀土丙氨酸配合物[Ho2(Ala)4(H2O)8]Cl6和[ErY(Ala)4(H2O)8](ClO4)6 (Ala为丙氨酸),用量热和热分析方法研究了这两种配合物的热力学性质.用全自动高精密绝热量热计测定了在78～377 K温区内的低温热容.对于[Ho2(Ala)4(H2O)8]Cl6,在214～255 K温区内发现一固-固相变,其相变温度为235.09 K.对于[ErY(Ala)4(H2O)8](ClO4)6,在99～121 K温区内也发现一固-固相变,其相变温度为115.78 K. [Ho2(Ala)4(H2O)8]Cl6固-固相变焓为3.02 kJ• mol－1,相变熵为12.83 J•K－1•mol－1； [ErY(Ala)4(H2O)8](ClO4)6 固-固相变焓为1.96 kJ•mol－1,相变熵为16.90 J•K－1•mol－1.同时,用TG技术在40～800 ℃温区研究了两配合物的热稳定性.由TG/DTG曲线分析可知, [Ho2(Ala)4(H2O)8]Cl6从80 ℃到479 ℃热分解分两步完成, [ErY(Ala)4(H2O)8](ClO4)6从120 ℃到430 ℃热分解分三步完成.     

Calorimetric study and thermal analysis of [Gd4/3Y2/3(Gly)6(H2O)4](ClO4)6·5H2O and [ErY(Gly)6(H2O)4](ClO4)6·5H2O (Gly: glycin)

Two solid-state coordination compounds of rare earth metals with glycin, [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O and [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O were synthesized. The low-temperature heat capacities of the two coordination compounds were measured with an adiabatic calorimeter over the temperature range from 78 to 376 K. [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 342.90 K, while [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O melted at 328.79 K. The molar enthalpy and entropy of fusion for the two coordination compounds were determined to be 18.48 kJ mol⁻¹ and 53.9 J K⁻¹ mol⁻¹ for [Gd_4/3Y_2/3(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, 1.82 kJ mol⁻¹ and 5.5 J K⁻¹ mol⁻¹ for [ErY(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O, respectively. Thermal decompositions of the two coordination compounds were studied through the thermogravimetry (TG). Possible mechanisms of the decompositions are discussed.     

Phase Transitions in Crystalline [M(H2O)6](ClO4)2 (M=Mg,Mn, Fe,Co, Ni,Cu, Zn,Cd and Hg)

The results of DSC measurements in the temperature range 140–370 K on nine crystalline compounds of the type [M(H₂O)₆](ClO₄)₂, where M=Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd and Hg, are discussed. Anomalies detected in the DSC curves are related to the existence of solid-solid phase transitions and/or to the melting points of these compounds. In consequence of two different hypothetical structural modifications of [Fe(H₂O)₆](ClO₄)₂, two DSC curves are obtained. For the compounds with M=Fe, Cd and Hg, new phase transitions have been discovered. The transition temperatures of the other phase transitions are in good agreement with literature data obtained by adiabatic calorimetry. For the compounds with M=Mg, Ni and Cd, DTA measurements were also carried out and the melting points of theses compounds were established. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calorimetric study and thermal analysis of [ErY(Ala)4(H2O)8](ClO4)6 (Ala=ALANINE)

A solid complex of rare-earth compounds with alanine, [ErY(Ala)₄(H₂O)₈](ClO₄)₆ (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)₄(H₂O)₈](ClO₄)₆ was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase transition was determined to be 1.957 Kj mol^-1, 16.90 j mol^-1 k^-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550°C by use of the thermogravimetric and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from 120 and ended at 430°C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trimethylsilylation of Alcohols and Phenols,and Direct Acetylation of Silyl Ethers Catalyzed by Fe(ClO4)3.6H2O

In this article, a mild and efficient protocol for the trimethylsilylation of various aliphatic and benzylic alcohols and phenols with trimethylsilyl chloride using a catalytic amount of ferric perchlorate at room temperature and relatively short reaction times in good to excellent yields is reported. Direct acetylation of trimethylsilyl ethers catalyzed with Fe(ClO ₄ ) ₃ .6H ₂ O(0.02 mmol)/Fe(ClO ₄ ) ₃ SiO ₂ (0.2 g) using acetic anhydride at ambient temperature is also reported.     

Kinetics of the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O

The thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages. The kinetics of the particular stages thermal decomposition have been evaluated. The R_N and/or A_M models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods are very close. The calculated activation energies were in air: 96 kJ mol^–1 (R_1.575, stage I); 101 kJ mol^–1 (Ain1.725 stage II); 185 kJ mol^–1 (A _2.9, stage III) and in argon: 66 kJ mol^–1 (A _1.25, stage I); 87 kJ mol^–1 (A _1.825, stage II); 133 kJ mol^–1 (A _2.525, stage III).     

Phase transitions of polycrystalline [Fe(H2O)6](ClO4)3 and [Cr(H2O)6](ClO4)3 studied by DSC

The effects of heat treatment on soymilk protein denaturation were studied by differential scanning calorimetry (DSC) and electrophoresis. Transition behavior of soymilk was studied by DSC. Three endotherms were found in DSC heating curves; the transition observed at around 70°C is attributed to the denaturation of 7S (b-conglycinin) and the transition at around 90°C is to 11S (glycinin). The denaturation temperature increased with the increasing soymilk protein content. The change of electrophoretic patterns after heat treatments indicated that soy proteins were dissociated into subunits, some of which coalesced. When the heating temperature is below their denaturation temperature, the protein fractions cannot completely be denatured even after heat exposure for extended periods of time. This revised version was published online in August 2006 with corrections to the Cover Date.     

稀土脯氨酸配合物[RE2(L-Pro)6(H2O)4](ClO4)6的标准生成焓测定

合成了两种稀土高氯酸盐与L 脯氨酸配合物的晶体.经热重、差热、化学分析及对比有关文献,知其组成是[Pr2(L Pro)6(H2O)4](ClO4)6和[Er2(L Pro)6(H2O)4](ClO4)6,质量分数为99.24％和98.20％.选用RE(NO3)3•6H2O(RE=Pr,Er)、L Pro、NaClO4•H2O和NaNO3作辅助物,使用具有恒温环境的反应热量计,以2 mol•L－1 HCl作溶剂,分别测定了[2RE(NO3)3•6H2O＋6L Pro＋6NaClO4•H2O]和{[RE2(L PrO)6(H2O)4](ClO4)6＋6NaNO3}在298.15 K时的溶解热.设计一热化学循环求得化学反应的反应焓ΔrHm分别是：63.904 kJ•mol－1和91.017 kJ•mol－1,经计算得配合物[RE2(L Pro)6(H2O)4](ClO4)6(s)在298.15 K时的标准生成焓ΔfHm(298.15 K)分别是－6 594.78 kJ•mol－1和－6 532.87 kJ•mol－1.     

The effect of experimental methods and measurement conditions on values of the kinetic parameters of [Co(NH3)6]2(C2O4)3·4H2O

Using the thermal decomposition of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O as a basis, the paper presents results which show how computed values of kinetic parameters are influenced by experimental conditions (ambient atmosphere, sample mass, linear heating rate) when using the non-isothermal methods and the Coats-Redfern (CR) modified equation. It also illustrates the influence of the experimental methods i.e. non-isothermal and isothermal (conventional) methods and also a quasiisothermal-isobaric one which can be recognised as equivalent to Constant Rate Thermal Analysis (CRTA). The results obtained have confirmed the significant influence of the experimental parameters as well as that of the experimental method used on the estimated values of kinetic parameters. The correlation between activation energy (E) and sample mass (m) or heating rate (β) is generally of a linear nature:E=a+bx     

Low-temperature heat capacity and standard enthalpy of formation of neodymium glycine perchlorate complex [Nd2(Gly)6(H2O)4](ClO4)6·5H2O

Rare-earth perchlorate complex coordinated with glycine [Nd₂(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O was synthesized and its structure was characterized by using thermogravimetric analysis (TG), differential thermal analysis (DTA), chemical analysis and elementary analysis. Its purity was 99.90%. Heat capacity measurement was carried out with a high-precision fully-automatic adiabatic calorimeter over the temperature range from 78 to 369 K. A solid-solid phase transformation peak was observed at 256.97 K, with the enthalpy and entropy of the phase transformation process are 4.438 kJ mol⁻¹ and 17.270 J K⁻¹ mol⁻¹, respectively. There is a big dehydrated peak appears at 330 K, its decomposition temperature, decomposition enthalpy and entropy are 320.606 K, 41.364 kJ mol⁻¹ and 129.018 J K⁻¹ mol⁻¹, respectively. The polynomial equations of heat capacity of this compound in different temperature ranges have been fitted. The standard enthalpy of formation was determined to be −8023.002 kJ mol⁻¹ with isoperibol reaction calorimeter at 298.15 K.     

Tetracyanonickelate compounds as sorptive materials and the substitution of their H2O content by D2O

The compounds NiNi(CN)₄·3,5H₂O and Ni(NH₃)₂Ni(CN)₄·H₂O have been studied to examine the possibility of substituting their H₂O or NH₃ content by D₂O. Contact with D₂O was performed after heating the compounds to several temperatures. Depending on the degree of decomposition of the original compounds different ranges of substitution were possible. In such manner the compounds NiNi(CN)₄·3,5D₂O, NiNi(CN)₄·5D₂O, Ni(NH₃)₂Ni(CN)₄·D₂O, and Ni(D₂O)₂Ni(CN)₄·D₂O were prepared and thermally they were less stable than the original ones. The substitution by D₂O is in agreement with the sorptive properties of the original tetracyanonickelate against different organic compounds using GC, since these could substitute the guest component and sometimes also the ligands during their decomposition.     

A comparison of quantitative theoretical results of the bonding in Ni(CO)4 and Ni(N2)4

Using non-empirical calculations the details of bonding in Ni(CO)₄ and in the analogous Ni(N₂)₄ are investigated.For Ni(CO)₄ some previous results are confirmed. In the calculation on Ni(N₂)₄ the close resemblance with Ni(CO)₄ is quite remarkable. The main difference is contained in the fact that carbon has a lower -electron density than nitrogen and that therefore the *-orbital in CO is lower in energy and geometrically more favourable for back donation.From the calculations we find a difference in metal-ligand bond energy between the carbonyl complex and the dinitrogen complex of approximately 18 kcal/mol.     

Simultaneous thermoanalytical investigations of (C6H5)4AsCl and (C6H5)4PCl under air and argon atmospheres

The thermoanalytical curves of (C₆H₅)₄AsCl (I) and (C₆H₅)₄PCl (II) were generated simultaneously by using a Netzsch simultaneous thermal analyser 409 under static air and dynamic argon atmospheres. The ranges of thermal stability of I and II were found to be 145–310°C and 137–365°C, respectively, and their melting points to be 261 and 278°C. The DTA profiles of I and II differ and can be used for their distinction.     

Low-temperature heat capacities and thermodynamic properties of rare-earth triisothiocyanate hydrates (III) —Sm(NCS)3 · 6H2O, Gd(NCS)3 · 6H20, Yb(NCS)3 · 6H20 and Y(NCS)3 · 6H20

The heat capacities of four RE isothiocyanate hydrates, Sm(NCS)₃, · 6H₂0, Gd(NCS)₃ · 6H₂0, Yb(NCS)₃, · 6H₂O and Y(NCS)₃, · 6H₂0, have been measured from 13 to 300 K with a fully-automated adiabatic calorimeter. No obvious thermal anomaly was observed for the above-mentioned compounds in the experimental temperature ranges. The polynomial equations for calculating the heat capacities of the four compounds in the range of 13–300 K were obtained by the least-squares fitting based on the experimentalC _P, data. TheC _P, values below 13 K were estimated by using the Debye-Einstein heat capacity functions. The standard molar thermodynamic functions were calculated from 0 to 300 K. Gibbs energies of formation were also calculated. Project supported by the National Natural Science Foundation of China.     

Synthesis and thermal investigation of Na2Cd(SO4)2·2H2O

The synthesis and thermal decomposition of Na₂(SO₄)₂·2H₂O in both air and nitrogen are described. The synthesis was performed by two different procedures, but in both cases the same product was obtained, corresponding to the general formula given above. The crystals obtained were investigated by methods of X-ray powder diffraction, and chemical and thermal analysis. The differences in thermal decomposition in air and nitrogen are discussed.     

Degradation thermique et etude vibrationnelle de MII(NH4)4(P3O9)2x4H2O(M II=Cu2+, Ni2+, Co2+)

We have studied the thermal behaviour under atmospheric pressure of isotypic tetrahydrate cyclotriphosphates M^II(NH₄)₄(P₃O₉)₂x4H₂O (M ^II=Cu, Ni and Co), between 25 and 1400°C, by X-ray diffraction, thermal analyses (TG and DTA) and infrared spectrometry. This study shows that the series of the compounds M^II(NH₄)₄(P₃O₉)₂x4H₂O (M ^II=Cu, Ni and Co) after elimination of water, in two different stages, and ammonia leads, at 400°C to cyclotetraphosphate M₂ ^IIP₄O₁₂ crystallized and to a thermal residue with a formula H₄P₄O₁₂ which undergoes under a thermal degradation by evolving water and pentoxide phosphorus. The kinetic characteristics of the dehydration and elimination of ammonia have been determinated. The vibrational spectra of Cu(NH₄)₄(P₃O₉)₂x4H₂O were examined and interpreted, in the domain of the valency frequencies, on the basis of the crystalline structure of its isotypic compound Co(NH₄)₄(P₃O₉)₂x4H₂O whose cycle has the site symmetry C₁, of our results of the calculation of the IR frequencies and the successive isotopic substitutions of the equivalent atoms (3P, 3Oi and 6Oe belonging to the P₃Oi₃Oe₆ ring) of the P₃O₉ ³⁻ cycle with high symmetry D_3h. This revised version was published online in August 2006 with corrections to the Cover Date.     

New Borate‐citrate: Synthesis,Structure, and Properties of Sr[B(C6H5O7)2](H2O)4·3H2O

Single crystals of Sr[B(C₆H₅O₇)₂](H₂O)₄ · 3H₂O, a new borate‐citrate material, were grown with sizes up to 8 × 6 × 2 mm by slow evaporation of water at room temperature. The structure of Sr[B(C₆H₅O₇)₂](H₂O)₄ · 3H₂O was determined by single‐crystal X‐ray diffraction. It crystallizes in the monoclinic space group P2₁/c, with a = 11.363(3) Å, b = 18.829(4) Å, c = 11.976(3) Å, β = 110.736(3)°, and Z = 4. The SrO₈ dodecahedra, BO₄ tetrahedra and citrate groups are linked together to form chains. The compound was characterized by IR and UV/Vis/NIR transmittance spectroscopy as well as thermal analysis.     

Etude de la deshydratation de Ca(H2PO4)2·H2O et de sa reaction avec CaSO4 par ATD-ATG couplees

The dehydration of Ca(H₂PO₄)₂·H₂O was examined with simultaneous DTA and TG. This dehydration permitted clearly the apparation of the following phases: Ca(H₂PO₄)₂·0.5H₂O, Ca(H₂PO₄)₂, Ca₃(HP₂O₇)₂, Ca₂HP₃O₁₀ et Ca(PO₃)₂. The reaction of Ca(H₂PO₄)₂·H₂O and CaSO₄ was also examined with the same technics. It was found that the decomposition of CaSO₄ takes place for relatively low temperature (between 600°C and 800°C).     

Phase polymorphism of [Ni(DMSO)6](BF4)2 studied by differential scanning calorimetry

The tetrafluoroborate of hexadimethylsulfoxidenickel(II) was synthesized and studied by differential scanning calorimetry. Seven solid phases of [Ni(DMSO)₆](BF₄)₂ were revealed. Specifically, six phase transitions of the first order were detected between the following solid phases: stable KIb → stable KIa at T _C6 = 335 K, metastable KIIb → metastable KIIa at T _C5 = 368 K, metastable KIII → overcooled phase KI at T _C4 = 378 K, metastable KIIa → overcooled phase KI at T _C3 = 396 K, stable KIa → stable KI at T _C2 = 415 K and stable KI → stable K0 at T _C1 = 433 K. [Ni(DMSO)₆](BF₄)₂ begins decomposition at 440 K with loss of one DMSO molecule per formula unit forming [Ni(DMSO)₅](BF₄)₂ (phase L0) which melts next in two steps in the temperature range 550–593 K. From the entropy changes connected both with melting and with phase transitions, it can be concluded that phases KI, overcooled KI and K0 are orientationally dynamically disordered (ODIC) crystals. Stable phases KIb, KIa and metastable phase KIII are ordered solid phases. Metastable phase KIIa and metastable phase KIIb are more or less ordered solid phases.