Chemical routes to oxides: alkoxidevs. alkoxide–acetate routes: synthesis, characterization, reactivity and polycondensation of MNb2(OAc)2(OPri)10(M=Mg, Cd, Pb) species

Abstract

The molecular constitution of solutions containing niobium alkoxides and divalent metal acetates M(OAc)₂ (M=Mg, Ba, Pb, Zn, Cd) has been examined. The heterometallic aggregates MNb₂(µ-OAc)₂(µ-OPrⁱ)₄(OPrⁱ)₆ (M=Mg 1, Cd 2, Pb 3a) have been isolated and characterized by elemental analysis, FTIR, multinuclear NMR (¹H, ¹³C, ²⁰⁷Pb, ¹¹³Cd) and by single-crystal X-ray diffraction for M=Mg and Cd. The magnesium derivative crystallizes in the monoclinic system, space group P2₁ /c with the unit-cell parameters a=21.238(5), b=10.127(10), c=24.861(3) Å, β=107.77(2)° and Z=4. The thermal stability of the various species has been investigated. Condensation is induced thermally for PbNb₂(OAc)₂(OPrⁱ)₁₀ . The reactivity between MNb₂(µ-OAc)₂- (µ-OPrⁱ)₄(OPrⁱ)₆ (M=Pb, Mg) and other metallic species has been evaluated. A terheterometallic compound, PbMgNb₂O(OAc)₂(OPrⁱ)₁₀ has been isolated. Whereas no reaction is observed between Ba(OAc)₂ and Nb(OPrⁱ)₅ , the reaction between metal alkoxides affords BaNb₂(OPrⁱ)₁₂(PrⁱOH)₂ . Its reactivity shows that the absence of an assembling acetate ligand induces facile separation between the metals. Results of the hydrolysis experiments of 1–3a are given. The powders have been analyzed by TG, SEM–EDX, light scattering and XRD. The merit of the assembling acetate ligand for avoiding the segregation of the metals is emphasized.