Coordination of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone to zinc and cadmium: Monotonic and non-monotonic bond length variations for [H(sebenzimMe)]2MCl2 complexes (M = Zn, Cd, Hg)

Abstract The reactions of 1-methyl-1,3-dihydro-2 H -benzimidazole-2-selone, H(sebenzim Me ), towards the zinc and cadmium halides, MX 2 (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzim Me )] 2 MX 2 , which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N–H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzim Me )] 2 ZnX 2 and [H(sebenzim Me )] 2 CdX 2 (X = Cl, Br), exhibit two intramolecular N–H⋯X interactions, whereas the iodide derivatives, [H(sebenzim Me )] 2 ZnI 2 and [H(sebenzim Me )] 2 CdI 2 , exhibit only one intramolecular N–H⋯I interaction. Comparison of the M–Se and M–Cl bond lengths of the chloride series, [H(sebenzim Me )] 2 MCl 2 (M = Zn, Cd, Hg), indicates that while the average M–Cl bond lengths progressively increase as the metal becomes heavier, the variation in M–Se bond length exhibits a non-monotonic trend, with the Cd–Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzim Me )] 2 CdCl 2 , [H(sebenzim Me )] 3 CdCl 2 ·[H(sebenzim Me )] 4 CdCl 2 , which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI 2 and H(sebenzim Me ) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzim Me )][H(benzim Me )]CdI 2 , a transformation that is associated with cleavage of the C–Se bond.