The preparation and structures of group 12 (Zn, Cd, Hg) complexes of the soft tripodal ligand hydrotris(methimazolyl)borate (Tm)

Complexes of the hydrotris(methimazolyl)borate ligand (Tm) have been prepared with zinc, cadmium and mercury halides. Complexes of type [M(Tm)X] were obtained and characterised by NMR and mass spectrometry. X-ray crystallographic analysis of [Zn(Tm)X] (X = Cl, Br, I) reveals a symmetrical coordination mode of the ligand, but no significant change with different halides, which sit on the approximate C₃ axes of the complexes. The structures of [M(Tm)Br] (M = Cd, Hg) are isomorphous with one another. Again, the ligand is symmetrically coordinated to the metal, but the halide is now significantly displaced from the approximate C₃ axis of the M(Tm) unit, resulting in what approximates to a trigonal pyramidal geometry. Unlike in most distorted mercury structures, little bond length expansion (towards two- or three-coordinate geometries) occurs. This is ascribed to the strong affinity of the thione donors for Hg.