Spectroelectrochemical Study of some //3-Oxo-//-acetato Trinuclear Rhodium(III) and Iridium(III) Complexes

Masato Tominaga, Isao Taniguchi Department of Applied Chemistry, Faculty of Engineering, Kumamoto University, Kurokami, Kumamoto 860, Japan Dedicated to Prof. Hitoshi Ohtaki on the occasion o f his 60th birthday Z. Naturforsch. 50b, 551-557 (1995); received October 5, 1994 Trinuclear Complexes, Rhodium Complexes, Iridium Complexes, dn-ipji Interaction, Spectroelectrochemistry, Mixed Valence State New trinuclear rhodium(III) complexes, [Rh3(//3-0)(/i-CH3C00)6(L)3]+ (L = imidazole (Him), 1-methylimidazole (Meim), and 4-methylpyridine (Mepy)) have been prepared. The Him, Meim, and Mepy complexes show reversible one-electron oxidation waves at E1/2 = +1.12, +1.12, and +1.28 V vs Ag/AgCl, respectively, in acetonitrile. Electronic absorption spectra of the one electron oxidized species of these complexes and [Rh3(M3-0)(M-CH3C 0 0 )6(py)3]+ (py = pyridine) (E1/2 = +1.32 V ) were obtained by spectroelectrochemical techniques. While the Rh3(III,III,III) states show no strong visible absorption, the Rh3(III,III,IV ) species give a band at ca. 700 nm (e = 3390-5540 mol dm“3 cm“ 1). [Ir3(«3-0)(//-CH3C00)6(py)3]+ with no strong absorption in the visible region, shows two reversible one-electron oxidation waves at +0.68 and +1.86 V in acetonitrile. The electronic absorption spectrum of the one-electron oxidized species (Ir3(III,III,IV )) also shows some absorption bands (688 nm (e, 5119), 1093 (2325) and 1400 (ca. 1800)). It is suggested that the oxidation removes an electron from the fully occupied anti-bonding orbital based on metal-d7r-/̂ 3-0-pjr interactions, the absorption bands of the (III,III,IV ) species being assigned to transitions to the a«r/-bonding orbital.