Molecular geometries of disilane, silylgermane and digermane. Is there a discrepancy between experiment and theory?

Equilibrium geometries of the staggered conformers of disilane, silylgermane, and digermane were located at the CCSD(T), CCSD, CISD, MP2, DFT, and HF levels of theory, using a number of valence double- and triple-zeta basis sets augmented by polarization functions. Contrary to doubts expressed by Oberhammer, Lobreyer and Sundermeyer (OLS), the correlated levels of theory, used in conjunction with valence triple-zeta basis sets augmented by f-polarization functions on heavy atoms, are capable of reproducing all experimental parameters that are well established. The present results described a microwave HGeH bond angle in Ge2H6 that is 2° larger than the somewhat questionable experimental value. The theoretical data presented suggest that the assumptions by OLS of intrinsically related GeH and SiH bond lengths and of equal HSiH and HGeH angles in H3SiGeH3 are not justified.