Studies on solid state reactions of coordination compounds

A series of tetranuclear Mo(W)-Ag mixed-metal clusters have been synthesized by makinguse of the solid state reactions of[NH_4]_2[MYS_3](M=Mo,W;Y=O,S),AgX(X=Cl,Br,I)and(n-Bu)_4NX'(X'=Cl,Br),two of which[(n-Bu)_4N]_3[MoOS_3Ag_3Br_4](1)and[(n-Bu)_4N]_3[WS_4Ag_3Cl_4](2)have been structurally characterized by X-ray analysis.The crystal data:1,cubic,P 3m,a=12.093(4) ,Z=1,R=0.076;2,cubic,P 3m,a=12.059(2) ,Z=1,R=0.075.The clusteranion core[Ag_3MS_3X']of the two compounds can be viewed as a cube in which the four metal atomsand the four non-metal atoms are statistically distributed,respectively.Substitution reaction withPPh_3 ligand is also discussed for this type of tetranuclear clusters.     

Metal-pyridinecarboxaldehyde complexes—II Zinc and cobalt complexes in the solid state

The following zinc and cobalt bromide complexes of 2- and 4-pyridinecarboxaldehyde (PCA) were prepared and characterised: Two isomers of both CoBr₂(4-PCA)₂ and CoBr₂(4-PCA) were isolated. The coordination about the metals was inferred from diffuse reflectance spectra and magnetic moment measurements. Infrared data indicated that 2-PCA was a bidentate chelate in both complexes isolated, while 4-PCA was monodentate in all but one of the adducts.     

Studies of tetravalent acetylacetonato complexes—I: Coordination and properties in the solid state

Chelates between acetylacetone and tetravalent d⁰ ions (zirconium, cerium, hafnium, thorium, uranium and neptunium) have been prepared and investigated. Two isostructural series exist, both monoclinic. The conditions for formation of the two forms have been studied. Coordination and structure are discussed from available X-ray data and IR spectra.     

The effect of anions in the coordination spherè of Mg complexes ofN-acetyldehydrophenylalanyl-(S)-valine on the diastereoselectivity of hydrogenation

Diastereoselective hydrogenation in ethanol over Pd/C ofN-acetyldehydrophenylalanyl-(S)-valine (1) as complexes with Mg salts of strong acids gives predominantlyN-acetyl-(S)-phenylalanyl-(S)-valine (de up to 60%). In the case of complexes of1 with Mg salts of weak acids, the sign of asymmetric induction changes. Data of¹⁹F NMR spectroscopy ofN-acetyldehydro(p-fluorophenylalanyl)-(S)-valine indicate that in the former case, the anion of a strong acid does not enter the coordination sphere of the complex, whereas in the larter case, the anion of the weak acid does. The nature of the solvent also influences the reaction stereoselectivity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1704–1706, September, 1999.     

The effect of ligand basicity on the thermal stability of heterodinuclear NiII–ZnII complexes

Four complexes of the nuclear structure Ni^II–Zn^II were prepared with bis-N,N′-(salicylidene)-1,3-propanediamine (LH₂), bis-N,N′-(salicylidene)-2,2′-dimethyl-1,3-propanediamine (LDMH₂) and the reduced derivatives of these Schiff bases, bis-N,N′-(2-hydroxybenzyl)-1,3-propanediamine (L^HH₂), bis-N,N′-(2-hydroxybenzyl)-2,2′-dimethyl-1,3-propanediamine (LDM^HH₂). The complexes were characterized using IR spectroscopy, elemental analysis and thermogravimetric methods. The stoichiometry of the complex molecules were found to be NiL·ZnCl₂·(DMF)₂, NiLDM·ZnCl₂·(DMF)₂, NiL^H·ZnCl₂·(DMF)₂ and NiLDM^H·ZnCl₂·(DMF)₂. The molecular models of the complexes prepared with the reduced Schiff bases were determined according to the X-ray diffraction method. It is seen that in these complexes Ni(II) is in octahedral and Zn(II) is in tetrahedral coordination sphere. Ni(II) ion is coordinated between two nitrogen and two oxygen donors of the ligand and oxygen donors of the two DMF molecules. Zn(II) ion on the other hand is coordinated between two oxygen of the organic ligand forming two μ bonds. It also coordinates two Cl ions. The thermogravimetric analysis showed that the complex NiLDM^H·ZnCl₂·(DMF)₂ containing methyl groups is more stable than the other complex NiL^H·ZnCl₂·(DMF)₂ containing reduced Schiff base. The coordinative DMF molecules in NiLDM^H·ZnCl₂·(DMF)₂ were thermally cleaved. However, the cleavage of DMF molecules NiL^H·ZnCl₂·(DMF)₂ resulted in the thermal degradation of the complex. In order to explain the TG data of the ligands were titrated in non-aqueous medium and their basicity strengths were determined. It was found that the basicity of the ligands containing two methyl groups were stronger. It is understood that the two methyl groups increase the negative charge density on nitrogen causing an increase in complex stability.     

Studies on organolanthanide complexes: VIII. Synthesis and thermal decomposition of new σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes

1,1′-Trimethylenedicyclopentadienyl-early lanthanide chlorides, [C₅H₄CH₂)₃-C₅H₄]LnCl · THF, in THF at −70°C reacted with aryllithium or alkyllithium, producing seven new THF solvated LnC σ-bonded 1,1′-trimethylenedicyclopentadienyl-early lanthanide complexes. The yttrium analogue was also synthesized. Their structures were determined by elemental analysis, infrared spectra, mass spectra, ¹H NMR and thermoanalyses. The thermal decomposition of the complexes obtained was studied at ambient temperature or 100°C.     

Studies on outer-sphere electron transfer reactions of surfactant–cobalt(III) complexes with iron(II) in liposome (dipalmitoylphosphotidylcholine) vesicles

The effect of unilamellar vesicles of dipalmitoylphosphotidylcholine (DPPC), both below and above the phase transfer region, on the second-order rate constants for outer-sphere electron transfer between Fe²⁺ and the surfactant?Ccobalt(III) complexes, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺ and cis-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺ (en?=?ethylenediamine, trien?=?triethylenetetramine, C₁₂H₂₅NH₂?=?dodecylamine) was studied by UV?CVis absorption spectroscopy. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC. It is concluded that below the phase transition temperature, there is an accumulation of surfactant?Ccobalt(III) complexes at the interior of the vesicle membrane through hydrophobic effects, and above the phase transition temperature the surfactant?Ccobalt(III) complex is released from the interior to the exterior surface of the vesicle. Through isokinetic plots, we have established that the mechanism of the reaction does not alter during the phase transition of DPPC.     

Structural diversity of isothiocyanato Cd(II) and Zn(II) Girard’s T hydrazone complexes in solution and solid state: effect of H-bonding on coordination number and supramolecular assembly of Cd(II) complex in solid state

The isothiocyanato Zn(II) complex (1) and mixed isothiocyanato/thiocyanato Cd(II) complex (2) with the condensation product of 2-acetylpyridine and trimethylammoniumacetohydrazide chloride (Girard’s T reagent) (HLCl) were investigated both experimentally and theoretically. The crystal structures of both complexes showed tridentate N₂O coordination of hydrazine ligand. In complex 1 square-pyramidal coordination surrounding of Zn(II) consists of deprotonated hydrazone ligand and two isothiocyanato ligands, while in octahedral Cd(II) complex ligand is coordinated without deprotonation as a positively charged species and coordination geometry is completed with two N-coordinated and one S-coordinated NCS^? anions. NMR spectroscopy and molar conductivity results for Cd(II) and Zn(II) complexes indicated their instability in solution. DFT calculations were performed to explain coordination preference and stability of complexes 1 and 2 in solid state and in solution. The obtained Cd(II) complex is the first reported mononuclear pseudohalide/halide Cd(II) complex with quinoline-/pyridine-based hydrazone ligands possessing octahedral geometry in solid state. In this complex, H-bonding has significant impact on coordination number and supramolecular assembly in solid state.     

Studies on the effect of surfactants on the extraction rate by laser thermal lens spectrometry

The effect of different kinds of surfactants on the extraction process of Nile Blue-I- was investigated by laser thermal lens spectrometry . It was shown that the surfactants could accelerate or decelerate the extraction rate by varying the extractive's solubility and the interfacial tension of the extraction solution. The higher the concentration of surfactants was, the more obvious the effect.     

Studies on solid state reactions of coordination compounds——XLⅦ.Solid state syntheses and crystal structures of cluster compounds {Cu_3MoS_3I}(PPh_3)_3S and {Cu_3WS_3Br} (PPh_3)_3S

Reactions of [NH_4]_2[MS_4](M=Mo,W),CuX(X=Br,I)and PPh_3 in the solid state producedfour mixed-metal sulfur containing clusters{Cu_3MS_3X}(PPh_3)_3S(M=Mo,W;X=Br,I),two of which(1:M=Mo,X=I;2:M=W,X=Br)were structurally determined.Crystals of 1 and 2 are triclinic,space group P(1:a=11.895(3),b=13.107(1),c=20.473(2),α=74.95(6),β=84.87(8),γ=64.27(7)°,Z=2,V=2776.1 ,Rw=0.064 for 6443 observed reflections.2:α=11.876 (1),b=13.065 (2),c=20.325(2),α=74.95(1),β=85.39(1),γ=64.09(1)°,Z=2,V=2737.3,R_w=0.055 for 5303 observedreflections).The results of the structure determination showed that the central units of the two cubane-like cluster compounds are composed of four metal atoms and four non-metal atoms situated at alter-nate comers.The differences of cubane-like cluster compounds obtained from solid state reactions andfrom solution reactions are discussed.     

The precipitation of the lanthanide elements complexes with hexammine cobalt(III) cation—I: The sulfate complexes of the trivalent lanthanide elements

Precipitation behaviors of the trivalent lanthanide elements from (NH₄)₂SO₄ and H₂SO₄ solutions were studied using hexammine cobalt(III) cation as the precipitant. Trivalent lanthanide elements from La to Ho precipitate as crystalline complexes of the same composition, [Co(NH₃)₆][Ln(SO₄)₃]·nH₂O. The solubility increases rapidly with increase of the atomic number after a minimum at Nd, Sm and Eu. Somewhat different behavior of Ce(III) was observed.     

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni²⁺/Cr³⁺ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni²⁺/Cr³⁺ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ～400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 Å. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 Å). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 Å is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni⁰ crystallites with a size of ～5.5 nm and a specific surface area of ～7.0 m² g^?1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO₂. The catalysts with the ratio Ni²⁺/Cr³⁺ = 1/(2?3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.     

The precipitation of lanthanide elements complexes with hexammine cobalt(III) cation—II: The carbonate complexes of the trivalent lanthanide elements

Precipitation behaviors of the trivalent lanthanide elements and yttrium in potassium and ammonium carbonate solutions with addition of hexammine cobalt(III) chloride as the precipitant were examined. La to Tb in K₂CO₃ solution and La to Lu and Y in (NH₄)₂CO₃ solution precipitated as scarcely soluble crystalline complexes. Lighter lanthanide elements are more easily precipitated and their solubilities are smaller than the heavier ones. Three different compositions of the precipitates are formed, as follows: [I] [Co(NH₃)₆][Ln(CO₃)₃]·nH₂O, [II] [Co(NH₃)₆][Ln(CO₃)₃]·1/2[Ln₂(CO₃)₃]·nH₂O and [Co(NH₃)₆][Ln(CO₃)₃]·α[Co(NH₃)₆]₂(CO₃)₃·nH₂O(α=0.1–0.3)     

Synthesis, characterisation and solid state structures of α-diimine cobalt(II) complexes: Ethylene polymerisation tests

A series of cobalt(II) compounds of the type [CoX₂(α-diimine)] were synthesised by direct reaction of anhydrous CoCl₂ or CoI₂ and the corresponding α-diimine ligand, in CH₂Cl₂: [CoI₂(o,o′,p-Me₃C₆H₂-DAB)] (1), [CoI₂(o,o′-ⁱPr₂C₆H₃-DAB)] (2), (where Ar-DAB = 1,4-bis(aryl)-2,3-dimethyl-1,4-diaza-1,3-butadiene), and [CoCl₂(o,o′,p-Me₃C₆H₂-BIAN)] (3), [CoCl₂(o,o′-ⁱPr₂C₆H₃-BIAN)] (4), and [CoI₂(o,o′-ⁱPr₂C₆H₃-BIAN)] (5) (where Ar-BIAN = bis(aryl)acenaphthenequinonediimine). All compounds were characterised by elemental analyses, IR, mass spectrometry, and X-ray diffraction whenever possible. The crystal structures of compounds 2-4 showed, in all cases, distorted tetrahedral geometries about the Co, built by two halogen atoms and two nitrogen atoms of the α-diimine ligand. Compounds 3 and 4, as well as [CoCl₂(o,o′,p-Me₃C₆H₂-DAB)] (1a), and [CoCl₂(o,o′-ⁱPr₂C₆H₃-DAB)] (2a), were activated by methylaluminoxane (MAO) and tested as catalysts for ethylene polymerisation, showing low catalytic activities. Selected polyethylene (PE) samples were characterised by ¹H and ¹³C NMR and FT-IR spectroscopies, and by differential scanning calorimetry (DSC), revealing branching microstructures (2.5-5.5%).     

Studies on Agarofurans Ⅲ. The Synthesis of 3-Substituted Agarofurans

Agarotlirans were found to be bioactive on nervous system. 3,4-dihydroxy dihydroagarofuran (l)' is only one of this group of natural products, which has substituent on C3 position.We synthesized this compound by the reported nletllod' and tbund it to possess somespecific bioactivity on nervous system. In order to search for more active compounds, wedecided to modify agarofurans on C-3 position beginning with the synthesis of 14-nor-3oxodihydroagarofuran (2).In the initial stage of the synthes…     

Preparation of single-phase α-Fe(III) oxide nanoparticles by thermal decomposition. Influence of the precursor on properties

In this research, we present an experimental procedure to prepare single-phase α-Fe(III) oxide nanoparticles by thermal decomposition of five different precursors including: iron(III) citrate; Fe(C₆H₅O₇), iron(III) acetylacetonate; Fe(C₅H₇O₂)₃, and iron(III) oxalate; Fe(C₂O₄)₃, iron(III) acetate; Fe(C₂H₃O₂)₃, and the thermal curves obtained were analyzed. The influence of the thermal decomposition of precursors on the formation α-Fe₂O₃ was studied by differential thermal gravimetry and thermogravimetry. The synthesized powders were characterized by using X-ray diffraction and scanning electron microscopy. High quality iron oxide nanoparticles with narrow size distribution and average particle size between ca. 2 and 30 nm have been obtained. It was found that the iron precursors affect the temperatures of the pure α-Fe₂O₃ nanoparticle formation with different diameters; iron(III) citrate (29 nm), iron(III) acetylacetonate (37 nm), and iron(III) oxalate (24 nm).     

Studies on the non-isothermal kinetics of the thermal decomposition of [Cu(NBOCTB)][Cu(NO3)4]· H2O

The thermal decomposition process of the complex [Cu(NBOCTB)][Cu(NO₃)₄] H₂O has been studied by TG and DTG technique, and possible intermediates of the thermal decomposition have also been conjectured from the TG and DTG curves. The results suggest that the decomposition of the complex involves five steps: The non-isothermal kinetics of steps 1, 2 and 3 have been studied by means of the Achar and Coats-Redfern method based on TG and DTG curves. Step 1 is a Coring and Growth mechanism (n= 1), its kinetic equation may be expressed as: d/dt=Ae^–E/RT(1–). Steps 2 and 3 are both two order chemical reaction mechanisms, their kinetic equations can be expressed as: d/dt=Ae^–E/RT(1–)².This project was supported by the National Natural Science Youth Fundation of China.     

Thermal decomposition studies on cobalt(II) complexes of 4-N-(4’-antipyrylmethylidene)aminoantipyrine with varying counter ions

The phenomenological, kinetic and mechanistic aspects of the nitrate, chloride, bromide and iodide complexes of cobalt(II) with 4-N-(4-antipyrylmethylidene)aminoantipyrine (AA) have been studied by TG and DTG techniques. The kinetic parameters such as activation energy, pre-exponential factor and entropy of activation were computed. The rate controlling process at all stages of decomposition is random nucleation with one nucleus on each particle (Mampel model)