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

Abstract

Ab initio MO studies at the HF, MP2, and Becke3LYP levels on H-bridged tetrahedranes of the group 14 elements (A₄H₄, A = C, Si, Ge, Sn, Pb) with the 6-31G^∗ basis set for C and Si and LANL1DZ 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.