The quest for mixed-metal oxide precursors based on bismuth: synthesis and molecular structure of BiTi2(mu3-O)(mu-OPri)4(OPri)5 and [Bi2(mu-OPri)2(OPri)2(acac)2] (acac = acetylacetonate)
Journal article, 1997
Various routes to mixed-metal Bi-Ti species were investigated. Various heterometallic alkoxides could be isolated by using hydrolysis reactions. The mixed-metal alkoxide BiTi2(mu(3)-O)(mu-OPri)(4)(OPri)(5) was obtained by reaction between titanium isopropoxide and a bismuth oxoisopropoxide formed in situ by controlled microhydrolysis and subsequent alcoholysis of Bi(OBut)(3). It was characterised by X-ray crystallography, H-1 NMR and Fourier-transform IR spectroscopy. The structure is based on an isosceles triangular framework with a central triply bridging oxo ligand. Bismuth is four-co-ordinate with a stereochemically active lone pair. The titanium atoms are six-co-ordinate with a severely distorted octahedral environment. Synthesis and characterisation of the bismuth-titanium ethoxides BiTi2O(OEt)(9) and Bi4Ti3O4(OEt)(16) were achieved, as well as their evaluation as oxide precursors. The latter leads, after complete hydrolysis and thermal treatment at 450 degrees C, to the pure crystalline Bi4Ti3O12 perovskite phase. The synthesis and structural characterisation of [Bi-2(mu-OPri)(2)(OPri)(2)-(eta(2)-acac)(2)](x) (acac = acetylacetonate) are also reported. The basic structural unit is a dimer in which the five-coordinated metals are linked by dissymmetrical Bi-OR bridges. Each beta-diketonate is chelating one metal. Chains of dimers run along the c axis via terminal semibridging isopropoxide ligands, ensuring six-co-ordination for the bismuth atoms.