THEORETICAL-STUDY ON METAL NMR CHEMICAL-SHIFTS - GERMANIUM COMPOUNDS

Germanium chemical shifts were studied theoretically by the ab initio molecular orbital method. The compounds studied were GeMe(4)-Cl-x(x) and GeMe(4)-H-x(x)(x = 0-4). The calculated values of the germanium chemical shifts agreed well with the available experimental values. The germanium chemical shift is due to the p-electron mechanism that reflects the ligand electronic effect on the p-p* excitation term in the second-order paramagnetic term. For GeMe(4)-H-x(x), the chemical shift is almost linear to the number of the ligand, x. On the other hand, a U-shaped dependence is predicted for the chemical shifts of the GeMe(4)-Cl-x(x) series and is shown to be caused by the strong and nonadditive electron-withdrawing ability of the Cl ligand. The diamagnetic contribution is relatively small for the chemical shift and is determined solely by a structural factor. (C) 1994 John Wiley & Sons, Inc.