HETEROCHELATES OF RUTHENIUM(II) - ELECTROCHEMISTRY, ABSORPTION-SPECTRA, AND LUMINESCENCE PROPERTIES

A series of heterochelates [Ru(bpy)(2)(L-X)](ClO4) (1-6) derived from the schiff bases of o-aminophenol and p-substituted (X) benzaldehydes, HL-X (X=NO2, Cl, F, Me, OMe and NMe2) have been synthesized and chara cterized. Cyclic voltammograms of all the complexes, except 6 (X=NMe2) , exhibit a reversible Ru-II/Ru-III and an irreversible Ru-III/Ru-IV o xidation processes. In the case of 6, both the oxidation process take place reversibly. A linear correlation is obtained by plotting the E-1 /2, value of Ru-II/Ru-III couple against the Hammett sigma(+) paramete rs. The absorption spectra of the complexes are similar showing absorp tion bands due to d pi-pi() (bpy), Schiff base n-pi(*) and pi-pi(*) i ntraligand transitions. A linear correlation is also obtained between (v) over bar(max) (MLCT) and Delta E-1/2 (separation between the first oxidation and first reduction couples). The effect of solvents on the MLCT and n-pi() absorption bands have been studied. Fluorescent spec tral studies have shown that all the complexes luminesce at room tempe rature and the observed emission bands are due to metal-perturbed liga nd-centred transitions. (C) 1997 Elsevier Science Ltd.