Triel-hydride triel bond between ZX(3) (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 THMe3BMe3 (T=Si and Ge), indicating that the sp(2)-hydridized triel atom has a strong affinity for the T-H bond. The formation of THMe3BH3 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 THMe3BH3 (>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 THMe3AlMe3 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.