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1995 (1)
1Author    Kenta Takahashi, Keisuke Umakoshi, Akihiro Kikuchi, Yoichi Sasaki, Masato Tominaga, Isao TaniguchiRequires cookie*
 Abstract    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) (E 1 /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. esting because of their characteristic strong visible absorption and reversible multi-step redox behav­ iour [2-14]. It has been suggested that such char­ acteristic properties are associated with strong in-termetallic interactions through the central oxide bridge. The Ru(d^r)-^3 -0 (p jr) interaction is sig­ nificantly stronger than that of analogous tri­ nuclear complexes o f first row transition elements. The djr-pjr molecular orbitals shown in Fig. 1 have been proposed for the trinuclear ruthenium complexes [3,15,16], In the study of mixed ruthe-nium-rhodium complexes, it was suggested that a similar molecular orbital scheme should be appli­ cable to trirhodium and mixed ruthenium-rho-dium complexes [7]. Electronic states o f the oxo-centered triiridium (III) complexes [17,18] should also be considered in terms of the djr-pjr molec­ ular orbital scheme. Thus the oxo-centered tri­ metal complexes of heavy transition elements could be significantly different from those of first row transition elements with respect to the extent of metal-oxygen-metal interactions. The trinuclear 
  Reference    Z. Naturforsch. 50b, 551—557 (1995); received October 5 1994 
  Published    1995 
  Keywords    Trinuclear Complexes, Rhodium Complexes, Iridium Complexes, dn-ipji Interaction, Spectroelectrochemistry, Mixed Valence State 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-0551.pdf 
 Identifier    ZNB-1995-50b-0551 
 Volume    50