Rhenium(V) complexes with Schiff bases: Synthesis and reaction mechanisms

Summary Some isomers of the ReOX₂LPPh₃ complexes [X = Cl or Br and L =N-methylsalicylideneiminate,N-phenylsalicylideneiminate, halfN,N'-ethylenebis(salicylideneiminate) or 8-hydroxyquinolinate] have been synthesized and characterized. Two different mechanisms for reaction of thetrans-ReOX₃(PPh₃)₂ complexes (X = Cl or Br) with the Schiff bases are supported by qualitative studies on such parameters as the Schiff base ligand form, concentration of free triphenylphosphine ligand, reaction solvent and temperature.     

Rotational motions of biradical metal chelates in polar solvents

Models of motion continuously varying from random jumps to rotational diffusion have been tested to simulate the ESR lineshape of biradical metal chelates spin probes in the slow-motion region. The evidence of a diffusional regime for the molecular reorientation contrasts with the anomalous temperature dependence of the process.     

ESR linewidth in oriented solvents with two-angle-dependent distribution function

The linewidth theory for partially oriented molecules is extended to paramagnetic solutes subjected to a two-angle-dependent orienting potential V(β,γ). A perturbation approach is used to solve the diffusion equation and to calculate the zero-frequency spectral densities.     

Methyl dynamics studied by ENDOR spectroscopy: a new method

A new method for the investigation of methyl group rotation dynamics in free radicals in solids is described, based on the temperature dependence of the methyl protons ENDOR enhancement. The method is shown to work for hindering barriers of any height, and for both radicals trapped in single crystals and in powdered samples. As specific examples, the Arrhenius parameters for the methyl rotation in free radicals produced by γ-irradiation of 1-alanine and 4-methyl-2, 6 di-t-butyl-phenol are determined.     

On groups with all proper subgroups finite-by-abelian-by-finite

Archiv der Mathematik - We show that if all proper subgroups of a locally graded group G are finite-by-abelian-by-finite, then G contains a finite normal subgroup N such that all proper subgroups...     

Electroanalytical study of the kinetics of thefac-mer isomerization of [ReCl(CO)3(PMe2Ph)2]+ in acetonitrile

Summary The isomerization offac-[ReCl(CO)₃(PMe₂Ph)₂]⁺ to the corresponding meridional-trans isomer has been studied by electroanalytical techniques in MeCN solvent. Chronoamperometric and cyclic voltammetric data relative to the oxidation offac- andmer-[ReCl(CO)₃(PMe₂Ph)₂] allow the accurate determination of the very high kinetic rate constant for the isomerization and permit discussion of thermodynamic aspects of redox homogeneous chemical reactions involving species of the different redox couples arising from the anodic processes.     

Synthesis and X-ray crystal structure of tetraethylammonium bis[1,2-di(carbomethoxy)ethane-1,2-dithiolato]oxotechnetate(V)

Summary The (NEt₄)⁺[TcO{SCH(CO₂Me)CH(CO₂Me)}₂]^– compound has been prepared from technetium(V) gluconate and characterized by single crystal x-ray structural analysis (R factor=0.065).The compound crystallizes in the monoclinic space groupP2₁/c witha=12.722(3),b=13.820(4) andc=18.213(5) Å, =107.13(4)° andZ=4. In the complex the technetium atom is close to the center of the base of a square pyramid in which the oxo oxygen is at the apex and the four sulfur atoms form the basal plane. The Tc-S distances average 2.316 Å. The Tc=O distance is 1.672(6) Å. Considerations about the osteotropic behaviour of DMSA labelled with⁹⁹Tc are deduced from the reported results.     

Voltammetric behaviour of rhenium(I) complexes with phosphine and carbon monoxide ligands in acetonitrile solvent

Summary The anodic and cathodic behaviour of the complexesmer-[ReCl(CO)₃(PMe₂Ph)₂],fac[ReCl(CO)₃(PMe₂Ph)₂],mer-[ReCl(CO)₃(PPh₃)₂], and [ReCl(CO)₂(PMe₂Ph)₃] in acetonitrile solvent were studied using platinum and mercury electrodes. Cyclic voltammetry and controlled potential coulometry were the main electroanalytical techniques employed. The nature of the electrolysis products and of the electrode oxidation and reduction processes were investigated. In particular, [ReCl(CO)(MeCN)₂(PMe₂Ph)₃][ClO₄]₂, [ReCl₃(CO)₂(PMe₂Ph)₂], and a not completely defined rhenium(-I) complex were electrochemically synthesized and characterized by means of i.r. and¹H n.m.r. spectroscopy, and by elemental analysis.     

Pentane-2,4-dione complexes of technetium99

Summary Pentane-2,4-dionatotechnetium⁹⁹ complexes of the type PPh₄[TcX₄(acac)], TcBr₃(acac)PPh3, TcX₂(acac)₂, TcX₂ (acac) (PPh₃)₂, TcX(acac)₂ PPh₃ and Tc(acac)₃ (X=Cl or Br) have been prepared and characterized. Where possible, their configurations have been determined from elemental analyses, conductivity and magnetic susceptibility measurements, and by i.r. and u.v.-visible spectroscopy.