Ligand and coordination-plane distortions in platinum(II) complexes of isomers of dimethyl-2,2'-bipyridine.

Pseudo-square-planar platinum(II) complexes containing 4,4' (4,4'-Me(2)bipy), 5,5' (5,5'-Me(2)bipy) and 6,6' (6,6'-Me(2)bipy) isomers of dimethyl-2,2'-bipyridine (Me(2)bipy) were synthesized and structurally characterized to assess the effects of methyl-group position on structure. The Pt-N distances in (Me(2)bipy)PtCl(2) complexes fall in the typical range [2.017 (3)-2.032 (3) Angstroms]. Only minor distortions such as 2.4 and 5.5 degrees twisting of the two pyridyl rings in (4,4'-Me(2)bipy)PtCl(2) (I) and (5,5'-Me(2)bipy)PtCl(2) (II), respectively, occur. However, (6,6'-Me(2)bipy)PtCl(2) (III) is highly distorted: the two pyridyl rings in (III) have a large bowing angle (theta(B)) of 19.2 degrees . The presence of distortions in (III), but not in (I) and (II), is attributed to repulsions between the 6,6'-methyl groups and the cis chloro ligands. [(4,4'-Me(2)bipy)(2)Pt](BF(4))(2) (IV) undergoes a bow-incline deformation having a large theta(B) value (24.2 degrees), and the ligands are inclined relative to the coordination plane by 18.80 (13) degrees. Complex (IV) joins a small list of distorted bis-bipyridine complexes; this finding can be attributed to the unfavorable repulsions between the 6,6' hydrogen substituents of opposing ligands. Some of these complexes exhibit canting rather than bow-incline distortion, a trend suggesting that subtle solid-state effects determine the nature of the distortion.