Donor atom electrochemical contribution to redox potentials of square pyramidal vanadyl complexes.

A simple donor atom additivity relationship has been used to calculate the donor atom electrochemical contribution ( DEC ) of the O ac (acetylacetonate-enolic oxygen), O Ph (phenolic oxygen), S Ph (mercaptophenol sulfur), N am (deprotonate amide nitrogen), N im (imine nitrogen) and N py (pyridine nitrogen) to the redox processes of the square pyramidal vanadyl complexes. The study focuses on the amidate vanadyl complexes because of (a) their biological interest and (b) the existence of data from plethora complexes studied in great details. The electrochemical contributions for the vanadyl oxidation and reduction processes increase following the same order, O Ph ~ O ac(enolic) < S Ph ~ N am < N im < N py . These values predict the electrochemical potentials of square pyramidal vanadyl complexes with high accuracy. Octahedral complexes with the same equatorial environment show significant shift of the oxidation potentials to lower values. The DEC influence to the square pyramidal vanadyls' electrochemical potentials has been evaluated. [ABSTRACT FROM AUTHOR]