Synthesis of heterobimetallic tungsten acetylacetonate/alkoxide complexes and their application as molecular precursors to metal tungstates

A series of MW₂(O)2(acac)₂ (OMe)₁₀ [M = Co (1), Ni (2), Mg (3), Zn (4)] have been synthesised and structurally characterised by X-ray crystallography. All the compounds share common structural features which are identical to the analogous molybdenum species, with four edge-sharing octahedra situated in the same plane, and incorporating two μ₃-bridging and four μ₂- bridging methoxide groups. The divalent metal M and tungsten have both octahedral coordination environments with six oxygen atoms. The structure of Na[Zn(acac)₃] (6), a by-product of a failed synthesis of 4, is also reported, and is a linear polymer in which [Zn(acac)₃]^₋ anions use all six oxygen atoms to link sodium cations either side of the anion.

Thermal decomposition of representative samples (1, 3) shows them to be single-source precursors for metal tungstates MWO₄. When the decomposition is carried out under an autogenerated pressure (RAPET) at 700 °C 1 forms CoWO₄ nanoparticles, along with WOx-filled carbon nanotubes and amorphous carbon, while 3 forms MgWO₄ nanoparticles and rods, though the latter lack a carbon shell and are much shorter in length.