2,2'-Bipyridine compounds of group 14 elements: a density functional theory study.

The molecular and electronic structures of the 2,2'-bipyridine containing series of group 14 compounds (a) MF4(bpy); (b) MCl2(bpy)2 (c) MCl2(bpy); (d) M(bpy)2; (e) Si(bpy)3; and (f) M(bpy)3 (M = C, Si, Ge, Sn, Pb) have been calculated using density functional theory (DFT). Where possible, geometry optimized structures are compared with their experimentally determined structures. In general, good to excellent agreement is observed. It is shown that the three successive one-electron reductions within the experimentally known series Si(bpy)3 are ligand-based and the Si center has a +IV oxidation state throughout. Hence, these species have the electronic structures Si(IV)(bpy(•))3 (S = 1/2), Si(IV)(bpy(•))2(bpy(2-)) (S = 0), Si(IV)(bpy(•))(bpy(2-))2 (S = 1/2), and Si(IV)(bpy(2-))3 (S = 0). Similarly, it is shown that the crystallographically characterized compound Si(bpy)2 (S = 0) possesses the electronic structure Si(IV)(bpy(2-))2, which contains a tetravalent Si ion and two (bpy(2-))(2-) dianions. It should not be described as Si(0)(bpy(0))2. For the heavier Ge, Sn, and Pb congeners the divalent state, characterized by a stereochemically active electron pair, becomes increasingly significant and dominates in 4-coordinate Sn and Pb species.