Molecular precursors for ferroelectric materials:: Synthesis and characterization of Bi2M2(μ-O)(sal)4(Hsal)4(OEt)2 and BiM4(μ-O)4(sal)4(Hsal)3(OiPr)4 (sal = O2CC6H4O, Hsal = O2CC6H4OH) (M = Nb, Ta)

Reactions I between triphenyl bismuth, salicylic acid, and niobium or tantalum ethoxide have been explored. Four new coordination complexes incorporating bismuth and the group 5 metals niobium or tantalum have been synthesized and characterized spectroscopically, by elemental analysis, and by single crystal X-ray diffraction. The new complexes are Bi2M2(mu-O)(sal)(4)(Hsal)(4)(OEt)(2) (1a, M = Nb; 1b, M = Ta) and BiM4(mu-O)(4)(sal)(4)(Hsal)(3)(OiPr)(4) (sal = O(2)CC(6)H(4-)2-O, Hsal = O2CC6H4-2-OH) (2a, M = Nb; 2b, M = Ta). Complexes 1 a and 1b are isomorphous, as are 2a and 2b. The thermal and hydrolytic decomposition of 1 a has been explored by DT/TGA and powder X-ray diffraction, while scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the morphology and composition of the oxides. The heterobimetallic molecules are completely converted to the amorphous bimetallic oxide by heating to 500 degreesC in air. Decomposition of 1a or 1b at 650 degreesC produces the metastable high temperature form of BiNb4 as the major crystalline oxide phase. Heating samples of la to 850 degreesC favors conversion of the materials to the low temperature phase as well as disproportionation into Bi5Nb3O15 and Nb2O5. Thermal decomposition of la and lb produces porous oxides, while hydrolytic decompostion of the complexes has been shown to produce nanometer scale bimetallic oxide particles. The potential of the complexes to act as single-source precursors for ferroelectric materials is considered.