Structural, spectroscopic, magnetic and thermal properties in the [SrM(C3H2O4)2(H2O)(5)]center dot 2 H2O (M = Mn, Fe, Co, Ni) system: Precursors of SrMO3-x mixed oxides

The [SrM(C3H2O4)(2)(H2O)(7)] (M=Mn, Fe, Co, Ni) compounds have been prepare d and characterised by chemical analysis and X-ray diffraction. The crystal structure of [SrCo(C3H2O4)(2)(H2O)(5)]. 2 H2O has been solved [monoclinic, P2(1)/c, Z = 4, a = 6.880(1), b = 14.360(2), c = 15.800(2) Angstrom. beta = 101.69(1)degrees]. The compound exhibits a three-dimensional chain/snake structure consisting of -CoO6-[SrO7](proportional to)-CoO6- repeating units parallel to the [0 1 1] and [0 -1 1] directions. UV/Vis data are consisten t with the cations being in high-spin octahedral symmetry. Magnetic measure ments show antiferromagnetic interactions for all compounds with approximat e 0 values of -0.5 K, except for the cobalt compound (-24.5 K) where the de crease of the chi(m) T curve can also be attributed to the spin-orbit coupl ing. Thermal analyses performed in air and under nitrogen show three consec utive steps: dehydration, ligand pyrolysis, and inorganic residue evolution . Thermal treatments in tubular furnaces were performed in order to obtain pure SrMO3-x phases. In all cases the oxides are nonstoichiometric and oxyg en-deficient with structures related to that of perovskite. Lower temperatu res and reaction times than those given in the literature have been used wh en using the ceramic method. These "soft" treatments gave rise to homogeneo us particles of small grain size.