H-bridged structures for tetrahedranes A4H4 (A=C, Si, Ge, Sn, and Pb)

Ab initio MO studies at the HF, MP2, and Becke3LYP levels on H-bridged tetrahedranes of the group 14 elements (A(4)H(4), A = C, Si, Ge, Sn, Pb) with the 6-31G* basis set for C and Si and LANLlDZ and quasirelativistic pseudopotential basis sets for Ge, Sn, and Pb are reported. As expected, the classical T-d structure 1 is more stable than all the other tetrahedrane alternatives for C4H4. The triply hydrogen bridged structure 2 (C-3v) is found to be more stable for Si, Ge, and Sn. Pb4H4 prefers the four H-bridged structure 8 (C-s). However, the calculations with the quasirelativistic pseudopotential basis set show the quadruply H-bridged D-2d structure 7 to be the most stable structure for Ge, Sn, and Pb. Thus the structures derived from the transition metal organometallic chemistry are competitive for heavier elements (Si to Pb). The periodic behavior begins only with the second period; Li to Ne, are the exceptions. Suggestions for the realization of these H-bridged structures for Pb from NaPb are discussed.