Structural and Electronic Studies of Substituted m-Terphenyl Group 12 Complexes.

The effects of para-substitution on the structural and electronic properties of four series of two-coordinate m-terphenyl Group 12 complexes (R-Ar(#))(2)M (M = Zn, Cd, Hg; R = t-Bu 1-3, SiMe(3) 4-6, Cl 7-9, CF(3) 10-12, where R-Ar(#) = 2,6-{2,6-Xyl}(2)-4-R-C(6)H(2) and 2,6-Xyl = 2,6-Me(2)C(6)H(3)) have been investigated. X-ray crystallography shows little structural variation across the series, with no significant change in the C-M-C bond distances and angles. However, considerable electronic differences are revealed by heteronuclear nuclear magnetic resonance (NMR) spectroscopy; a linear correlation is observed between the (113)Cd, (199)Hg, and (1)H (2,6-Xyl methyl protons) NMR chemical shifts of the para-substituted complexes and the Hammett constants for the R-substituents. Specifically, an upfield shift in the NMR signal is observed with increasingly electron-withdrawing R-substituents. Density functional theory (DFT) calculations are employed to attempt to rationalize these trends.