Vibrational coupling in oxo-centred trinuclear clusters:: oxygen-16/18 isotopic substitution studies of [Fe3IIIO(O2CC(CH3)3)6(py)3][FeCl4] and [Fe2IIIFeIIO(O2CC(CH3)3)6(py)3]

IR spectra are reported for the compounds [Fe3O(O2CC(CH3)(3))(6)(py)(3)][FeCl4] and [Fe3O(O2CC(CH3)(3))(6)(py)(3)]. Using isotopic substitution at the central oxygen atom, the assignments of the in-plane and out-of-plane vibrations of this atom are confirmed, and coupling is demonstrated between the in-plane modes nu(as)(Fe3O) and carboxylate deformation modes rho(r)(C-CO2). (C) 2000 Elsevier Science B.V. All rights reserved.