Lower main-group element complexes with a soft scorpionate ligand: the structural influence of stereochemically active lone pairs

The syntheses and structures of complexes of the fifth period elements indium and antimony, and the sixth period element bismuth with the soft scorpionate ligand. hydrotris(methimazolyl)borate (Tm^Me) are reported. A considerable variety of structural motifs were obtained by reaction of the main-group element halide and NaTm^Me. The indium(III) complexes took the form [In(K³-Tm^Me)₂] ⁺. This motif could not, however, be isolated for antimony(III), the dominant product being [Sb(K³-Tm^Me)(K¹-Tm ^MeX] (X = Br, I). An iodo-bridged species [Sb(K³-Tm ^Me)I(μ2-I)]₂, analogous to a previously reported bismuth complex, was also isolated. Reaction of antimony(III) acetate with NaTm^Me results in a remarkable species in which three different ligand binding modes are observed. In each antimony complex the influence of the nonbonded electron pair is observed in the structure. Bismuth halides form complexes analogous to those of antimony, with directional lone pairs, but in addition, reaction of Bi(NO₃)₃ with NaTm^Me results in a complex with a regular S₆ coordination sphere and a nonstereochemically active lone pair. Comparisons are drawn with known Tm ^Me complexes of As, Sn, and Bi in which the stereochemical influence of the lone pairs is negligible and with Tm^Me complexes of Te and Bi in which the lone pairs are stereochemically active. This study highlights the ability of Tm^Me to coordinate in a variety of modes as dictated by the metal centre with no adverse effects on the stability of the complexes formed.