SYNTHESIS, CHARACTERIZATION AND ELECTROCHEMICAL REDUCTIONS OF OXO-CENTERED, CARBOXYLATE-BRIDGED TRIIRON COMPLEXES, [FE-3(MU(3)-O)-(MU-O2CR)(6)L-3]X (R = ME, BU-T, PH, CH2CL, CCL3, CH2CN OR 4-NO2C6H4, L = PY, 3-H(2)NPY, 4-H(2)NPY, 3-NCPY, 4-NCPY OR 4-CH(2)CHPY, X = CLO4- OR NO3-)

A range of oxo-centred, carboxylate-bridged triiron complexes of gener al formula [Fe3O(O2CMe)(6)L-3]X (L = py, 3-H(2)Npy, 4-H2Npy 3-NCpy, 4- NCpy or 4-CH(2)CHpy, X = ClO4-) and [Fe3O(O2CR)(6)(py)(3)]X (R = Bu-t, Ph, CH2Cl, CCl3, CH2CN or 4-NO2C6H4, X = ClO4- or NO3-) has been synt hesized, some for the first time. The [Fe3O(O2CPh)(6)(py)(3)]NO3 compl ex (as its dichloromethane solvate) has been the subject of a room-tem perature single-crystal X-ray study. The redox behaviour of these comp lexes has been investigated by cyclic voltammetry in 0.2 mol dm(-3) [N Bu4][PF6]-dichloromethane, in the presence and absence of free L (wher e L is pyridine or substituted pyridine). These complexes in general d isplay a chemically reversible one-electron reduction to the neutral m ixed-valence species at +0.5 to -0.2 V, vs. Ag-AgCl, provided an exces s of free L is present. The reversible potential of the [Fe3O(O2CMe)(6 )L-3](+/0) and [Fe3O(O2CR)(6)(py)(3)](+/0) reductions varies linearly with the pK(a) of L and -O2CR. A second reduction was also detected at more negative potentials. Only for R = CH2CN the second reduction bec omes chemically reversible in the presence of free pyridine, such that the monoanion, [Fe3O(O2CR)(6)(py)(3)](-), is stable on the timescale of the voltammetric experiment. Where solubility and stability permitt ed, the [Fe3O(O2CMe)(6)L-3] and [Fe3O(O2CR)(3)(py)(3)] complexes have been electrogenerated in situ. The mixed-valence species display an ex tremely broad, low intensity (epsilon approximate to 60-100 dm(3) mol( -1) cm(-1)) band in the 7000-8000 cm(-1) region of the electronic spec trum.