OXO-CENTERED TRINUCLEAR CARBOXYLATO COMPLEXES CONTAINING MIXED-METAL AND MIXED-VALENCE CLUSTERS CR-III2M-IIO AND MN-III2M-IIO (M = CO, NI OR MN)

New mixed-metal complexes [Cr(III)2M(II)O(O2CCH3)6(C5H5N)3].solv and [Mn(III)2M(II)O(O2CCH3)6-(C6H5N)3].solv (M = Co, Ni or Mn; solv = solvent) have been prepared and characterised by X-ray diffraction and IR spectroscopy. The complex [Mn(III)2Co(II)O(O2CCH3)6(C5H5N)3].CH3CO2H crystallises in the trigonal system, space group R32, with a = 17.614(18), b = 10.470(12) angstrom and Z = 3. In-plane vibrations of the central M(III)2M(II)O unit of each complex are assigned and used to establish the electronic character of the mixed-valence manganese(III,III,III) complex. In contrast to the iron(III,III,II) analogue, this complex shows no tendency towards equalisation of the frequencies of A1 and B2 components of V(asym(M(III)2M(II)O), and it is evidently strongly valence-localised at room temperature.