Influence of benzannulation on metal coordination geometries: Synthesis and structural characterization of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium bromide, {[TmMeBenz]Cd(μ-Br)}2

The tris(2-mercapto-1-methylbenzimidazolyl)hydroborato cadmium complex, {[TmMeBenz]Cd(μ-Br)}2, may be synthesized via the reaction of [TmMeBenz]K with CdBr2. X-ray diffraction demonstrates that {[TmMeBenz]Cd(μ-Br)}2 exists as a dimer, which is in marked contrast to the monomeric structure of the non-benzannulated counterpart, [TmMe]CdBr, and thereby demonstrates that benzannulation of tris(2-mercapto-1-methylbenzimidazolyl)hydroborato ligands can have a distinct impact on the molecular structure of their metal complexes. In accord with this observation, density functional theory calculations indicate that the benzannulated dimers, {[TmMeBenz]Cd(μ-X)}2 (X = Cl, Br, I), are more stable with respect to dissociation than are their non-benzannulated counterparts, {[TmMe]Cd(μ-X)}2. Furthermore, the calculations also indicate that the stability of the dimer depends on the nature of X, such that the dimer becomes more stable in the sequence I < Br < Cl.