Triel-hydride triel bond between ZX3 (Z = B and Al; X = H and Me) and THMe3 (T = Si, Ge and Sn)

Complexes between THMe3 (T=Si, Ge and Sn) and ZX(3) (Z=B and Al; X=H and Me) have been characterized using MP2/aug-cc-pVTZ calculations. These complexes are chiefly stabilized by a triel-hydride triel bond with the T-H bond pointing to the -hole on the triel atom. The triel-hydride interaction is mainly attributed to the charge transfer from the T-H bond orbital to the empty p orbital of the triel atom. These complexes are very stable with a large interaction energy (>10 kcal mol(-1)) excluding THMe3<bold>BMe</bold>3 (T=Si and Ge), indicating that the sp(2)-hydridized triel atom has a strong affinity for the T-H bond. The formation of THMe3<bold>BH</bold>3 results in proton transfer, characterized by conversion of orbital interaction and large charge transfer (ca 0.5e). The large deformation is primarily responsible for the abnormally greater interaction energy in THMe3<bold>BH</bold>3 (>30 kcal mol(-1)) than in the AlH3 analogue. Methyl substitution on the triel atom weakens the triel-hydride interaction and causes a larger interaction energy in THMe3<bold>AlMe</bold>3 with respect to its BMe3 counterpart. Most of these interactions possess characteristics of covalent bonds. Polarization makes a contribution to the stability of most complexes nearly equivalent to the electrostatic term.