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.