Interplay between lead carboxylate and Ti or Zr isopropoxides in solution routes to perovskites: synthesis, molecular structures and reactivity of single source non-oxo Pb–Zr and Pb–Ti carboxylatoalkoxides supported by 2-ethylhexanoate ligands

Abstract

The reactions between Ti(OⁱPr)₄ and Zr₂(OⁱPr)₈(HOⁱPr)₂, respectively, and lead 2-ethylhexanoate Pb(O₂CC₇H₁₅)₂ have been investigated at rt and by heating. The initial mixed-metal species, characterized by single-crystal X-Ray diffraction, were adducts namely Pb₄Zr₄(µ-O₂CR′)₈(µ-OR)₆(µ₃-OR)₂(OR)₈(OHR)₂1 and Pb₂Ti₄(µ-O₂CR′)₄(µ-OR)₆(µ₃-OR)₂(OR)₈2 (R′ = CHCH(Et)C₂H₄Me, R = ⁱPr) independently of the stoichiometry used. They are the first Pb–Ti and Pb–Zr non-oxo carboxylatoalkoxides reported. 1 is also the first Pb–Zr species based on an alkoxide-carboxylate ligand set matching the PbZrO₃ stoichiometry. Both structures are centrosymmetric with six-coordinate transition metals, as required for the perovskite, and are based on triangular M₂Pb cores (M = Zr, Ti). The lead centers display quite high coordination numbers, six and seven. The thermal and hydrolytic condensation reactions of 1 and 2 were investigated. Heat treatment of 2 and elimination of the volatiles under vacuum afforded Pb₂Ti₃(µ₄-O)(µ₃-O)(µ-O₂CC₇H₁₅)₂(µ-OⁱPr)₆(OⁱPr)₄3 resulting from extrusion of Ti(OⁱPr)₄ and scrambling of carboxylate ligands. Characterization of the various compounds was achieved by elemental analysis, FT-IR, ¹H and ²⁰⁷Pb NMR.