Methylzinc tetrahydroborate: physical and chemical properties and crystal structure at low temperature

Abstract

Methylzinc tetrahydroborate, MeZnBH₄, has been prepared by two routes and initially characterized by elemental analysis and its spectroscopic properties. The structure has been determined by X-ray crystallography at 150 K [trigonal, space group R3c, a=b= 15.831(10), c= 8.36(2)Å, Z= 18, R= 0.072] to reveal helical polymers in which MeZn⁺ and BH₄^– units alternate, with the latter functioning as a bidentate ligand with respect to both of the adjacent metal atoms. It thus resembles the structure of solid Be(BH₄)₂ with the difference that the zinc is five-co-ordinated, the Me and H ligands adopting a distorted square-pyramidal geometry. Chemical properties of methylzinc tetrahydroborate investigated include its thermal decomposition and its reactions with ammonia, dimethyl sulfide, triphenylphosphine and CO; disproportionation into Me₂Zn and Zn(BH₄)₂ appears to be a common feature of its chemistry.