Exchange and magnetic dipole-dipole interactions in bi- and triradical complexes of Al(III), Ga(III), In(III), and Sn(IV) witho-semiquinones. PM3 calculation

Semiempirical (PM3 with CI) calculations of exchange interactions for the triradical complexes of Al(III), Ga(III), and In(III) and the biradical complex of Sn (IV) with o-semiquinones are carried out. The results are in agreement with both qualitative theoretical assumptions and experimental data. The calculations indicate that the superexchange via the unoccupied porbitals of the central metal ion predominantly determines the multiplicity of the ground states of the complexes. Zero-field splitting constants D are calculated; they also agree well with experimental data. Deceased. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 6, pp. 1053–1060, November–December, 1997.     

Coordination of aza heterocycles with macroheterocyclic metal complexes in amphiprotic media: III. Kinetics and mechanism of inner-sphere ligand exchange in (tetraphenylporphyrinato)chromium(III)

Inner-sphere replacement of alcohols by imidazole and its derivatives in the complex (acetato)-(tetraphenylporphyrinato)chromium(III) was studied by electronic absorption spectroscopy. The rate constants and activation parameters of the process were calculated. The entering ligand structure was shown to affect the reaction rate, while the alcohol nature (departing ligand) does not influence the kinetic parameters of the process to an appreciable extent. Regression analysis revealed participation of imidazole and ethanol in the rate-determining stages. The kinetic equation for the inner-sphere axial substitution implies interaction of a free alcohol molecule with that coordinated to chromium, followed by replacement of the associate by the heteroring. Mathematical processing of the kinetic data in terms of the proposed solvolytic association-dissociation mechanism gave the rate constants for particular stages of the process and showed an extremal relation between the rate constant and composition of the solvent.