John L. Bear

A study of some rhodium(II) acetate adducts

Abstract Several rhodium(II) acetate adducts have been prepared and their spectral and thermal properties investigated. The ligands used to form the adducts were water, diethylsulfide, dimethylsulfoxide, pyridine, triethylarsine, ammonia, and the ethyl and methyl amines. The spectral transitions of the adducts in the visible region were dependent on the nature of the ligand forming the adduct. The thermal properties of the adducts were studied using thermogravimetric analysis and differential scanning calorimetry.

The thermodynamics and kinetics of the polymerization of silicic acid in dilute aqueous solution

Abstract The polymerization of silicic acid has been investigated at a pH of 8.5 and initial monomer concentration of 300 p.p.m. The rate of polymerization was determined at 25, 30, 35, 40 and 45°C so that the activation energies could be calculated. The activation energies were found to be −16±4 kcal/mole in the 25–35°C region and 14±4 kcal/mole in the 35–40°C region. The negative activation energy is explained by assuming a pre-equilibrium step involving a hydrogen bonded species. The thermodynamic parameters were also determined for the polymerization process. A mechanism has been proposed for the polymerization reaction.

The formation kinetics of some lanthanide oxalate complexes

Abstract The kinetics of formation and dissociation were determined for the one-to-one lanthanide oxalate complexes by a pressure jump technique. The rates were determined as a function of temperature and the activation parameters calculated. The results suggest that the rate-determining step is the loss of a water molecule from the inner co-ordination sphere of the lanthanide metal ion. The trend in the rate of formation within the lanthanide series indicates a decrease in coordination number in the lanthanide series occurring in the region from europium to holmium. The results correlate well with other rate data, conductivity data and thermodynamic studies on lanthanide complex formation in solution.

The thermal decomposition of some rhodium(II) carboxylate complexes

Abstract Rhodium(II) propionate, benzoate, trichloroacetate and trifluoroacetate have been prepared and studied by several thermoanalytical techniques. The thermal decomposition products of the propionate and benzoate complexes were determined using thermogravimetric analysis and mass spectrometry. Properties of the trifluoracetate complex were studied by mass spectrometry and magnetic measurements. Several adducts of the complexes were prepared.

A kinetic study of the reaction of rhodium(II) acetate with trifluoroacetic acid

Abstract The reaction of rhodium(II) acetate with excess trifluoroacetic acid was followed by 1H NMR. Identification of the intermediate compounds in the exchange process was accomplished by use of mass spectrometry. The reaction was found to be a stepwise exchange of trifluoroacetate for the acetate cage. Rate constants measured have a ratio of approximately 1:2:0·1:0·025 for k1:k2:k3:k4. The first substitution has a labilizing effect on the system causing the second substitution to occur twice as fast as the first. After the formation of Rh2(OOCCH3)2(OOCCF3)2, the reaction proceeds at a much slower rate until the completely exchanged rhodium(II) trifluoroacetate is formed.

The X-ray crystal structure of the trans-dl-1,2-diaminocyclohexane-(N-methyliminodiacetato)platinum(II) complex

Abstract The crystal structure of the trans-dl-1,2-diaminocyclohexane(N-methyliminodiacetato)platinum(II) complex has been determined by X-ray diffraction. It has the following parameters: space group P21/c (monoclinic), a=11.272(5), b=14.034(7), c=10.163(5) A, β=116.13(3)°, Z=4. The slightly distorted square plane of the Pt includes two nitrogens of the diamine in cis positions and one oxygen and one nitrogen from N-methyliminodiacetate ion. The PtN and PtO distances average 2.038 and 2.013 A, respectively. An intricate system of hydrogen bonds which involves every hydrogen atom not attached to carbon was observed. The molecule is a zwitterion and the charge density on the unbound carboxylate is probably stabilized through this series of strong hydrogen bonds.

Thermoanalytical characterization of solid-state Co(II)-, Ni(II)- and Cu(II)-4(5)-aminoimidazole-5(4)-carboxamide complexes

Abstract Derivatives of the imidazole ring are very useful models to better understand the coordination properties and the reaction mechanisms of biologically important systems. Six different complexes of 4(5)-aminoimidazole-5(4)-carboxamide (AIC) with Co(II), Ni(II) and Cu(II) have been synthesized and characterized by elemental analysis, UV–VIS and IR spectroscopies. The thermal stability was determined by differential scanning calorimetry (DSC) and by thermogravimetric analysis (TGA), and the decomposition mechanisms were investigated by evolved gas analysis (EGA).

The thermal decomposition of dimethylsulfoxide and diethylsulfide adducts of rhodium(II) acetate

Abstract The thermal decomposition reactions of Rh 2 (OOCCH 3 ) 4 · 2S(CH 2 CH 3 ) 2 and Rh 2 (OOCCH 3 ) 4 · 2DMSO have been studied by thermogravimetric analysis, differential scanning calorimetry and dynamic reflectance spectroscopy. The intermediates, including a new type of adduct, and the products have been isolated and characterized. The decomposition sequence was found to be: Rh 2 (OOCCH 3 ) 4 ·2L( s ) → Rh 2 (OOCCH 3 ) 4 ·L( s ) + L( g ) → Rh 2 (OOCCH 3 ) 4 ( s ) + L( g ) → 2Rh°( s ) + 2CO( g ) + 3HOOCCH 3 ( g ). The spectral, magnetic and thermodynamic properties of the intermediate adducts, Rh 2 (OOCCH 3 ) 4 · S(CH 2 CH 3 ) 2 and Rh 2 (OOCCH 3 ) 4 · DMSO, have been investigated.

Electrochemical characterization of a rhodium(II) dimer with N-phenylacetamido bridging ligands

Etudes des reactions redox de Rh 2 [C 6 H 5 NOCCH 3 ) 4 , dimere, en milieu non aqueux ((CH 3 ) 3 CO, CH 2 Cl 2 , CH 3 CN et PrCN), par volteammetrie a impulsions differentielles, par voltammetrie cyclique et par polarographie

The thermodynamic and kinetic stabilities of some Tetra-μ-carboxylatodirhodium(II) adducts

Abstract The stability constants and forward and reverse rate constants have been determined for adduct formation reactions involving tetra-μ-acetato, tetra-μ-propionate and tetrakis-μ-methoxyacetatodirhodium(II) with the ligands pyridine, picolinic acid, niacin and isonicotinic acid. The experimentally observed stability trend is isonicotinic acid > pyridine ⋍ niacin ⪢ picolinic acid. It appears that the π bonding ability of the ligands determines the order of stability of these adducts. The variation of the stabilities of the adducts formed from different tetra-μ-carbox-ybtodlrhodium(II) complexes and a given ligand is related to an inductive effect as well as the lipophylic nature of the carboxylate side chain. The more hydropholic character of the propionate species apparently exerts a desolvating effect at the two axial positions resulting in a more rapid ligand exchange.