Oxo-centred trinuclear carboxylato complexes containing mixed-metal and mixed-valence clusters CrIII2MIIO and MnIII2MIIO (m = Co, Ni or Mn)

Abstract

New mixed-metal complexes [Cr^III₂M^IIO(O₂CCH₃)₆(C₅H₅N)₃]·solv and [Mn^III₂M^IIO(O₂CCH₃)_6–(C₅H₅N)₃]·solv (M = Co, Ni or Mn; solv = solvent) have been prepared and characterised by X-ray diffraction and IR spectroscopy. The complex [Mn^III₂Co^IIO(O₂CCH₃)₆(C₅H₅N)₃]·CH₃CO₂H crystallises in the trigonal system, space group R32, with a= 17.614(18), b= 10.470(12)Å and Z= 3. In-plane vibrations of the central M^III₂M^IIO unit of each complex are assigned and used to establish the electronic character of the mixed-valence manganese(III,III,II) 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^III₂M^IIO), and it is evidently strongly valence-localised at room temperature.