Studies on Mixed β-Diketonate/Isopropoxide Compounds of Zirconium and Hafnium, the X-ray Single-Crystal Structures of [M2(OPri)6(tmhd)2] (M = Zr, Hf):  Some Chemistry Important in the MOCVD of Oxides

Reactions of the homoleptic alkoxides [M(OPri)4·(PriOH)] (M = Zr or Hf) with different stoichiometric amounts of the β-diketone ligand tmhd-H (2,2,6,6-tetramethylheptane-3,5-dione) have been investigated. Crystalline, but powdery, materials with a stoichiometry close to [M(OPri)2(tmhd)2] have been isolated by reacting 2 mol of the β-diketone with 1 mol of the metal alkoxide; we present a full explanation based on the 1H NMR results for their behavior in solution. The compounds [M2(OPri)6(tmhd)2] [M = Zr (1b), and Hf (2b)] have been obtained from the exhaustive recrystallization of the above reaction mixture or as the products of the 3:1 stoichiometric reaction between [M(OPri)4.(PriOH)]2 and tmhd-H. Compounds 1b and 2b have been shown by X-ray crystallography to be isomorphous and are useful precursors for the deposition of the metal oxides by methods such as liquid injection CVD. The symmetrical, dimeric structure of the compounds, with one β-diketonate attached to each half of the dimer, may explain why the compounds show little or no tendency toward adventitious homogeneous reaction in MOCVD studies.