THE QUEST FOR MIXED-METAL OXIDE PRECURSORS BASED ON BISMUTH - SYNTHESIS AND MOLECULAR-STRUCTURE OF BITI2(MU(3)-O)(MU-OPRI)(4)(OPRI)(5) AND [BI-2(MU-OPRI)(2)(OPRI)(2)(ACAC)(2)]INFINITY (ACAC = ACETYLACETONATE)

Various routes to mixed-metal Bi-Ti species were investigated. Various heterometallic alkoxides could be isolated by using hydrolysis reacti ons. The mixed-metal alkoxide BiTi2(mu(3)-O)(mu-OPri)(4)(OPri)(5) was obtained by reaction between titanium isopropoxide and a bismuth oxois opropoxide formed in situ by controlled microhydrolysis and subsequent alcoholysis of Bi(OBut)(3). It was characterised by X-ray crystallogr aphy, H-1 NMR and Fourier-transform IR spectroscopy. The structure is based on an isosceles triangular framework with a central triply bridg ing oxo ligand. Bismuth is four-co-ordinate with a stereochemically ac tive lone pair. The titanium atoms are six-co-ordinate with a severely distorted octahedral environment. Synthesis and characterisation of t he bismuth-titanium ethoxides BiTi2O(OEt)(9) and Bi4Ti3O4(OEt)(16) wer e achieved, as well as their evaluation as oxide precursors. The latte r leads, after complete hydrolysis and thermal treatment at 450 degree s 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 st ructural unit is a dimer in which the five-coordinated metals are link ed by dissymmetrical Bi-OR bridges. Each beta-diketonate is chelating one metal. Chains of dimers run along the c axis via terminal semibrid ging isopropoxide ligands, ensuring six-co-ordination for the bismuth atoms.