CHEMICAL ROUTES TO OXIDES - ALKOXIDE VS. ALKOXIDE-ACETATE ROUTES - SYNTHESIS, CHARACTERIZATION, REACTIVITY AND POLYCONDENSATION OF MNB2(OAC)(2)(OPRI)(10) (M = MG, CD, PB) SPECIES

The molecular constitution of solutions containing niobium alkoxides a nd divalent metal acetates M(OAc)(2) (M = Mg, Ba, Pb, Zn, Cd) has been examined. The heterometallic aggregates MNb2(mu-OAc)(2)(mu-OPri)(4)(O Pri)(6) (M = Mg 1, Cd 2, Pb 3a) have been isolated and characterized b y elemental analysis, FTIR, multinuclear NMR (H-1,C-13,Pb-207,Cd-113) and by single-crystal X-ray diffraction for M = Mg and Cd. The magnesi um derivative crystallizes in the monoclinic system, space group P2(1) /c with the unit-cell parameters a=21.238(5), b=10.127(10), c=24.861(3 ) Angstrom,beta=107.77(2)degrees and Z = 4. The thermal stability of t he various species has been investigated. Condensation is induced ther mally for PbNb2(OAc)(2)(OPri)(10). The reactivity between MNb2(mu-OAc) (2)-(mu-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)((PrOH)-O-i)(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 meri t of the assembling acetate ligand for avoiding the segregation of the metals is emphasized.