Thermal behavior of some new chromium complexes with potential biological importance

Summary This paper reports the investigation of the thermal stability of three new complexes of Cr(III) with acrylate anion, [Cr₂(C₃H₃O₂)₄(OH)₂(H₂O)₄], [Cr₃O(C₃H₃O₂)₆(C₃H₄O₂)₃](C₃H₃O₂)×5H₂O and [Cr₂(C₃H₃O₂)₅(OH)] ×2H₂O, respectively. This type of complexes is important in proper carbohydrate and lipid metabolism of mammals. The thermal decomposition steps were evidenced. The thermal transformations are complex processes according to TG and DTG curves including dehydration and oxidative degradation of acrylate ion processes. The final product of decomposition is the chromium(III) oxide.     

Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

The crystal structures of [M₂(phen)₄(H₂O)₂(C₄O₄)]· C₄O₄· 8H₂O [M = Co²⁺ (1), Mn²⁺ (2); phen: 1,10-phenanthroline] complexes have been prepared and characterized by IR spectroscopy, thermal analysis and single X-ray diffraction techniques. Their structures consist of [Co₂(phen)₄(H₂O)₂(C₄O₄)]²⁺ (1) and [Mn₂(phen)₄(H₂O)₂(C₄O₄)]²⁺ (2) dinuclear cobalt(II) and manganese(II) cations, uncoordinated C₄O ₄ ^2? (SQ^2?) dianion and crystalization water molecules. In both complexes the metal ions have distorted octahedral geometry. The squarate adopts the μ-1,3 (1) and (2) bis(monodentate) coordination modes, the intradimer M–M separation being 8.053(7) Å (1) and 8.175(4) Å (2), respectively, while the other squarate acts as a counter anion. The voltammetric behaviour of complexes (1) and (2) was investigated in DMSO (dimethylsulfoxide) solution by cyclic voltammetry using n-Bu₄NClO₄ as supporting electrolyte. The complexes exhibit both metal and ligand centred electroactivity in the potential ?±1.75 V versus Ag/AgCl reference electrode. The dianion SQ^2? is oxidized in two consecutive steps to the corresponding radical monoanion and neutral form.     

Thermal studies of some biologically active oxovanadium(IV) complexes containing 8-hydroxyquinolinate and hydroxamate ligands

The thermal decomposition behaviours of oxovanadium(IV)hydroxamate complexes of composition [VO(Q)_2?n(HL^1,2)_n]: [VO(C₉H₆ON)(C₆H₄(OH)(CO)NHO)] (I), [VO(C₆H₄(OH)(CO)NHO)₂] (II), [VO(C₉H₆ON)(C₆H₄(OH)(5-Cl)(CO)NHO)] (III), and [VO(C₆H₄(OH)(5-Cl)(CO)NHO)₂] (IV) (where Q?=?C₉H₆NO^? 8-hydroxyquinolinate ion; HL¹?=?[C₆H₄(OH)CONHO]^? salicylhydroxamate ion; HL²?=?[C₆H₃(OH)(5-Cl)CONHO]^? 5-chlorosalicylhydroxamate ion; n?=?1 and 2), which are synthesised by the reactions of [VO(Q)₂] with predetermined molar ratios of potassium salicylhydroxamate and potassium 5-chlorosalicylhydroxamate in THF?+?MeOH solvent medium, have been studied by TG and DTA techniques. Thermograms indicate that complexes (I) and (III) undergo single-step decomposition, while complexes (II) and (IV) decompose in two steps to yield VO(HL^1,2) as the likely intermediate and VO₂ as the ultimate product of decomposition. The formation of VO₂ has been authenticated by IR and XRD studies. From the initial decomposition temperatures, the order of thermal stabilities for the complexes has been inferred as III?>?I > II?>?IV.     

Oxidation of coordinated olefins: the reactions of Cl2 with trichloro(ehtylene)platinate(II)

The oxidation of [PtCl₃(C₂H₄)]- by Cl₂ in aqueous solution, to yield CH₂ClCH₂OH and [PtCl₄]^2-, has been shown to proceed through the following sequence of steps: [PtCl₃(C₂H₄)] Cl₂Cl [PtCl₅(CH₂CH₂Cl)]^2-$\text{H}{}_2\text{O}\text{(HCl)}$ [PtCl₅(CH₂CH₂OH)]^2- → [PtCl₄^2- + CH₂ClCH₂OHEach of the steps and intermediates in this mechanistic sequence has been identified and characterized.     

[Mn(H2O)4(C4N2H4)][C6H4(COO)2] – Ein eindimensionales Koordinationspolymer mit kettenartigen [Mn(H2O)4(C4N2H4)]n2n+ Polykationen

[Mn(H₂O)₄(C₄N₂H₄)][C₆H₄(COO)₂] – An One‐Dimensional Coordination Polymer with Chain‐like [Mn(H₂O)₄(C₄N₂H₄)]_n²ⁿ⁺ Polycations Orthorhombic single crystals of [Mn(H₂O)₄(C₄N₂H₄)][C₆H₄(COO)₂] have been prepared in aqueous solution at room temperature. Space group Imm2 (no. 44), a = 1039.00(6) pm, b = 954.46(13) pm, c = 737.86(5) pm, V = 0.73172(12) nm³, Z = 2. Mn²⁺ is coordinated in a octahedral manner by four water molecules and two nitrogen atoms stemming from the pyrazine molecules (Mn–O 215.02(11) pm; Mn–N 228.7(4), 230.7(4) pm). Mn²⁺ and pyrazine molecules form chain‐like polycations with [Mn(H₂O)₄(C₄N₂H₄)]_n²ⁿ⁺ composition. The positive charge of the polycationic chains is compensated for by phthalate anions, which are accomodated between the chains. The phthalate anions are linked by hydrogen bonds to the polycationic chains. Thermogravimetric analysis in air revealed that the loss of water of crystallisation and pyrazine occurs in two steps between 130 and 245 °C. The resulting sample was stable up to 360 °C. Further decomposition yielded Mn₂O₃.     

Magnetic properties of nanocrystalline CuFe2O4 and kinetics of thermal decomposition of precursor

CuFe₂(C₂O₄)₃·4.5H₂O was synthesized by solid-state reaction at low heat using CuSO₄·5H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. The spinel CuFe₂O₄ was obtained via calcining CuFe₂(C₂O₄)₃·4.5H₂O above 400 °C in air. The CuFe₂(C₂O₄)₃·4.5H₂O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform FT-IR, X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer, and vibrating sample magnetometer. The result showed that CuFe₂O₄ obtained at 400 °C had a saturation magnetization of 33.5 emu g^?1. The thermal process of CuFe₂(C₂O₄)₃·4.5H₂O experienced three steps, which involved the dehydration of four and a half crystal water molecules at first, then decomposition of CuFe₂(C₂O₄)₃ into CuFe₂O₄ in air, and at last crystallization of CuFe₂O₄. Based on KAS equation, OFW equation, and their iterative equations, the values of the activation energy for the thermal process of CuFe₂(C₂O₄)₃·4.5H₂O were determined to be 85 ± 23 and 107 ± 7 kJ mol^?1 for the first and second thermal process steps, respectively. Dehydration of CuFe₂(C₂O₄)₃·4.5H₂O is multistep reaction mechanisms. Decomposition of CuFe₂(C₂O₄)₃ into CuFe₂O₄ could be simple reaction mechanism, probable mechanism function integral form of thermal decomposition of CuFe₂(C₂O₄)₃ is determined to be 1 ? (1 ? α)^1/4.     

Thermal studies on yttrium,neodymium and holmium oxalates

The thermal decomposition patterns of Y₂(C₂O₄)₃ · 9 H₂O, Nd₂(C₂O₄)₃ · 10 H₂O and Ho₂(C₂O₄)₃ · 5.5 H₂O have been studied using TG and DTG. The hydrated neodymium oxalate loses all the water of hydration in one step to give the anhydrous oxalate while Y₂(C₂O₄)₃ · 9 H₂O and Ho₂(C₂O₄)₃ · 5.5 H₂O involve four or more dehydration steps to yield the anhydrous oxalates. Further heating of the anhydrous oxalates results in the loss of CO₂ and CO to give the stable metal oxides.     

The unusual electrochemical behaviour of [Co8(CO)18C]2− compared to [M6(CO)15C]2− (M = Co,Rh) and [Fe6(CO)16C]2− carbido clusters

A variety of electrochemical reactions has been observed for the carbido-carbonyl clusters [Co₈(CO)₁₈C](NMe₃CH₂C₆H₅)₂, [Co₆(CO)₁₅C](NMe₃CH₂C₆H₅)₂, [Rh₆(CO)₁₅C](Et₄N)₂ and [Fe₆(CO)₁₆C](Et₄N)₂. The hexanuclear clusters undergo irreversible electrochemical oxidation and reduction steps, whereas the octacobalt species exhibits three electrochemically reversible one-electron steps. The relation between the redox properties and the structure of these clusters is discussed.     

Thermal decomposition of bismuth laurates

Summary Three bismuth compounds of lauric (dodecanic) acid: Bi₆O₄(OH)₄(C₁₁H₂₃COO)₆, Bi₆O₄(OH)₄ (C₁₁H₂₃COO)₆ nC₁₁H₂₃COOH and Bi(C₁₁H₂₃COO)₃ were synthesized. The thermogravimetry under quasi-isothermal conditions denotes the multi-step character of decomposition processes for compounds. Non-isothermal thermogravimetric data (obtained at two different rates of linear heating) were used for kinetic studies. Kinetic parameters were calculated only for chosen decomposition steps.     

IR and thermal studies on a new oxomolybdenum(VI) oxalato complex

A new molybdenum(VI) oxalato complex K₄(NH₄)₁₀[Mo₁₄O₄₂(C₂O₄)₇] (PAMO) was prepared and characterized by chemical analysis, IR spectral and X-ray studies. Its thermal decomposition was studied using TG, DTA and DTG techniques. The compound is anhydrous and decomposes between 235° and 335°C in three steps. The first and the second steps occur in the temperature ranges 235°–290°C and 290–310°C to give the intermediate compounds having the tentative compositions K₄(NH₄)₈[Mo₁₄O₄₂(C₂O₄)₆] and K₂(NH₄)₂[Mo₁₄O₄₂(C₂O₄)₃], respectively, the later than decomposing to give a mixture of potassium tetramolybdate and molybdenum trioxide at 335°C. DTA also shows a peak at 530°C which corresponds to the melting of potassium tetramolybdate. An examination of the products obtained at 340° and 535°C by chemical analysis, IR spectra and X-ray studies reveals them to be identical.The authors are grateful to Dr. M. C. Jain, Head of the Department of Chemistry, for providing research facilities.     

Preparation,Characterization and Solid State Thermal Studies of Cadmium(II) Squarate Complexes ofhane-1,2-diamine and its Derivatives

[CdL₃]C₄O₄ [L=ethane-1,2-diamine (en)], [CdL₂(H₂O)₂]C₄O₄ [L=N-methylethane-1,2-diamine (meen), N-ethylethane-1,2-diamine (eten), N-propylethane-1,2-diamine (pren), propane-1,2-diamine (pn) and N-methylpropane-1,2-diamine (ibn)] and [CdL₂(C₄O₄)] [L=N-isopropylethane-1,2-diamine (ipren)] have been synthesized by the addition of the respective diamine to finely powdered CdC₄O₄×₂H₂O and their thermal studies have been carried out in the solid state. [Cd(en)₃]C₄O₄ upon heating loses two molecules of diamine in two overlapping steps yielding Cd(en)C₄O₄ which upon further heating transforms to unidentified products. The diaquabis(diamine) species, [CdL₂(H₂O)₂]C₄O₄, show thermally induced deaquation-anation reaction in the solid state and thereby produce [CdL₂(C₄O₄)], which reverts on exposure to humid atmosphere (RH =90%) for 20–24 h. All the squarato bis(diamine) species, [CdL₂(C₄O₄)], on pyrolysis in the solid state transform to unidentified products through the formation of intermediates, CdL_1.5C₄O₄, (L=meen, pren and ipren), CdLC₄O₄ (L=meen, en, pren, ipren, pn and ibn) and CdL_0.5C₄O₄ (L=eten, pn and ibn). However, amongst the intermediates only the mono diamine species, CdLC₄O₄ can be isolated in pure form and the pyrolytic process is the only way to synthesize them. The monodiamine species can be stored in a desiccator as well as in an open atmosphere and proposed to have a polymeric structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Facile preparation of fullerenyl boronic esters

The fullerendiol C₆₀(OH)₂(OOt-Bu)₄ 1 reacts with various arylboronic acids ArB(OH)₂ to form fullerene-containing boronic esters C₆₀(O₂BAr)(OOt-Bu)₄ in up to 95% yield depending on the structure of aryl group. Bis(pinacolato)diboron (B(OCMe₂)₂)₂ also reacts with 1 to form C₆₀(O₂BB(OCMe₂)₂)(OOt-Bu)₄. The bisboronic ester C₆₀(O)(O₂BAr)₂(OOt-Bu)₂ was also obtained starting from a tetrahydroxyl fullerene derivative C₆₀(O)(OH)₄(OOt-Bu)₂. The fullerenyl boronic esters are moderately stable in air. Single crystal X-ray structure of C₆₀(O₂BPh)(OOt-Bu)₄ was obtained.     

Mono and dinuclear Pd(II) complexes with pyrazole and imidazole-type ligands Synthesis, characterization and thermal behaviour

The cyanate-bridged cyclopalladated compound [Pd(C²,N-dmba)(μ-NCO)]₂ (dmba=N,N-dimethylbenzylamine) reacts in acetone with pyrazole (pz), 3,5-dimethylpyrazole (dmpz), imidazole (imz) and 2-methylimidazole (mimz) to give [Pd₂(C²,N-dmba)₂(μ-NCO)(μ-pz)] (1), [Pd₂(C²,N-dmba)₂(μ-NCO)(μ-dmpz)] (2), [Pd(C²,N-dmba)(NCO)(imz)] (3) and [Pd(C²,N-dmba)(NCO)(mimz)] (4), respectively. The compounds were characterized by elemental analysis, IR spectroscopy and TG. The thermal decomposition of the compounds occurs in three consecutive steps and the final decomposition products were identified as Pd(0) by X-ray powder diffraction. The thermal stability order of the complexes is 2>3>1>4.     

Kinetic and thermodynamic study of the Na4(UO2)2(OH)4(C2O4)2 complex

The synthesis, the characterization, and the thermal decomposition of the dioxouranium(VI) ternary complex of formula Na₄(UO₂)₂(OH)₄(C₂O₄)₂, has been studied. The identification of the compound was performed by chemical analysis and by infrared spectrometry. Thermal decomposition of the compound occurs in several steps due to the decomposition of the salt to Na₂O and UO₃ oxides. The stoichiometry of the steps, hypothesized by means of the thermodynamic and kinetic parameters, is confirmed by the evolved gas analysis studied by FTIR spectrometer coupled to TG/DSC apparatus. Model‐fitting and model‐free kinetic methods have been used in kinetic analysis. The latter allows determining kinetic scheme. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 661–669, 2003     

Thermal decomposition of the oxo-diperoxo-molibdenum (VI)-potassium oxalate

The oxo-diperoxo-molibdenum(VI)-potassium oxalate, K₂[MoO(O₂)₂(C₂O₄)] was synthesized using an adapted version of the method suggested by Dengel. The thermal behavior of the synthesized complex was investigated by simultaneous thermal analysis TG/DTG/DTA, in air or nitrogen atmosphere, to identify and characterize the mass-loss decomposition processes. In addition, for the characterization of the observed decomposition steps, the FT-IR spectra for the initial complex, evolved gaseous compounds and isolated complex at 230 and 430/383 °C in air/nitrogen atmosphere, were recorded. On the 35–500 °C temperature range, the K₂[MoO(O₂)₂(C₂O₄)] complex presented three main decomposition steps, accompanied by mass-loss. The first degradation step is due to the elimination of one oxygen molecule, by the breaking of the peroxo groups, with the formation of an intermediary, like [MoO₃L]. The other two degradation steps can be attributed to the decomposition of the organic ligand, with the final formation of a stable metallic oxide.     

Synthesis and Structures of ansa‐Titanocene Complexes with Diatomic Bridging Units for Overall Water Splitting

The synthesis of a series of ansa‐titanocene dichlorides [Cp′₂TiCl₂] (Cp′=bridged η⁵‐tetramethylcyclopentadienyl) and the corresponding titanocene bis(trimethylsilyl)acetylene complexes [Cp′₂Ti(η²‐Me₃SiC₂SiMe₃)] is described. The ethanediyl‐bridged complexes [C₂H₄(C₅Me₄)₂TiCl₂] ( 2 ‐Cl₂) and [C₂H₄(C₅Me₄)₂Ti(η²‐Me₃SiC₂SiMe₃)] ( 2‐ btmsa; btmsa=η²‐Me₃SiC₂SiMe₃) can be obtained from the hitherto unknown calcocenophane complex [C₂H₄(C₅Me₄)₂Ca(THF)₂] ( 1 ). Furthermore, a heterodiatomic bridging unit containing both, a dimethylsilyl and a methylene group was introduced to yield the ansa‐titanocene dichloride [Me₂SiCH₂(C₅Me₄)₂TiCl₂] ( 3 ‐Cl₂) and the bis(trimethylsilyl)acetylene complex [Me₂SiCH₂(C₅Me₄)₂Ti(η²‐Me₃SiC₂SiMe₃)] ( 3 ‐btmsa). Besides, tetramethyldisilyl‐ and dimethylsilyl‐bridged metallocene complexes (structural motif 4 and 5 , respectively) were prepared. All ansa‐titanocene alkyne complexes were reacted with stoichiometric amounts of water; the hydrolysis products were isolated as model complexes for the investigation of the elemental steps of overall water splitting. Compounds 1 , 2 ‐btmsa, 2 ‐(OH)₂, 3 ‐Cl₂, 3 ‐btmsa, 4 ‐(OH)₂, 3 ‐alkenyl and 5 ‐alkenyl were characterised by X‐ray diffraction analysis.     

Theoretical study on inverse sandwiches [M(AIP)]2(C4H4) (M = V,Cr): High spin multiplicity of septet and nonet

The experimental synthesis of quintet [V(AIP)]₂(μ‐C₆H₆) and septet [Cr(AIP)]₂(μ‐C₆H₆) analogues provide a new strategy to produce high spin multiplicity by utilizing inverse sandwiches. Aiming to design higher spin multiplicity, [M(AIP)]₂(μ‐C₄H₄) (M = Cr, V) using C₄H₄ as central ligand are theoretically proposed. For [V(AIP)]₂(μ‐C₄H₄), the most stable isomer group contains the septet and the open‐shell singlet isomers, which have three unpaired electrons on each V atoms. For [Cr(AIP)]₂(μ‐C₄H₄), the most stable isomer group contains the septet and the nonet isomers, which have three and four unpaired electrons on each Cr atoms, respectively. The dissociation energies indicate that the above [M(AIP)]₂(μ‐C₄H₄) are as stable as the available [M(AIP)]₂(μ‐C₆H₆). It would be a reasonable strategy using C₄H₄ as central ligand to induce the higher spin multiplicity of inverse sandwiches.     

Redox properties of (RC2R')Co2(CO)6-nLn and reactivity of (RC2R')Co2(CO)6-nLn towards PPh3[LPPh3, P(OEt)3]

Cyclic voltammetric studies of clusters (C₅H₅-C₂C₆ H₄-R-p)Co₂(CO)6-n L_n[n=0,2; L=PPh₃, P(OEt)₃] and (RCH₂C)₂Co₂(CO₄) (PPh₃)₂ on Pt electrode are described. The primary reduction (0 / ?1) and oxidation (+ 1 / 0) steps are considered as a mono-electron process for all clusters. For the clusters (C₅H₅C₂C₆H₄-R-p)Co₂(CO)₆, a good linear relation between reduction potential E_p^red and Hammett constant σ_p of R in the clusters is found. For the clusters (RC₂R')Co₂(CO)₄L₂, their radical anions are extremely unstable at room temperature and fragment into a series of mononuclear species, one of which is (RC₂R')Co(CO)₂PPh₃. The reaction of radical anions of (RC₂R')Co₂(CO)_6–n (PPh₃)_n(n=0,2) with PPh₃ also produces mononuclear species (RC₂R')Co(CO)₂PPh₃ which has been detected by means of cyclic voltammetry and ESR. The influence of R on redox properties of clusters is discussed.     

Activation of Open‐Cage Fullerenes with Ruthenium Carbonyl Clusters

Reactions of the open‐cage fullerene C₆₃NO₂(Py)(Ph)₂ ( 1 ) with [Ru₃(CO)₁₂] produce [Ru₃(CO)₈(μ,η⁵‐C₆₃NO₂(Py)(Ph)₂)] ( 2 ), [Ru₂H(CO)₃(μ,η⁷‐C₆₃N(Py)(Ph)(C₆H₄))] ( 3 ), and [Ru(CO)(Py)₂₍η³‐C₆₃NO₂(Py)(Ph)₂)] ( 4 ), in which the orifice sizes are modified from 12 to 8, 11, and 15‐membered ring, through ruthenium‐mediated C?O and C?C bond activation and formation.