SPECTROELECTROCHEMICAL STUDY OF SOME MU(3)-OXO-MU-ACETATO TRINUCLEAR RHODIUM(III) AND IRIDIUM(III) COMPLEXES

New trinuclear rhodium(III) complexes, [Rh-3(mu(3)-O)(mu(3)-CH3COO)(6) (L)(3)](+) (L = imidazole (Him), 1-methylimidazole (Meim), and 4-methy lpyridine (Mepy)) have been prepared. The Him, Meim, and Mepy complexe s show reversible one-electron oxidation waves at E(1/2) = +1.12, +1.1 2, and +1.28 V vs Ag/AgCl, respectively, in acetonitrile. Electronic a bsorption spectra of the one electron oxidized species of these comple xes and [Rh-3(mu(3)-O)(mu-CH3COO)(6)(py)(3)](+) (py = pyridine) (E(1/2 ) = +1.32 V) were obtained by spectroelectrochemical techniques. While the Rh-3(III,III,III) states show no strong visible absorption, the R h-3(III,III,IV) species give a band at cn. 700 nm (epsilon = 3390-5540 mol dm(-3) cm(-1)). [Ir-3(mu(3)-O)(mu-CH3COO)(6)(py)(3)](+) with no s trong absorption in the visible region, shows two reversible one-elect ron oxidation waves at +0.68 and +1.86 V in acetonitrile. The electron ic absorption spectrum of the one-electron oxidized species (Ir-3(III, III,IV)) also shows some absorption bands (688 nm (epsilon, 5119), 109 3 (2325) and 1400 ten. 1800)). It is suggested that the oxidation remo ves an electron from the fully occupied anti-bonding orbital based on metal-d pi-mu(3)-O-p pi interactions, the absorption bands of the (III ,III,IV) species being assigned to transitions to the anti-bonding orb ital.