H-BRIDGED STRUCTURES FOR TETRAHEDRANES A(4)H(4) (A=C, SI, GE, SN, ANDPB)

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 quasirelati vistic pseudopotential basis sets for Ge, Sn, and Pb are reported. As expected, the classical T-d structure 1 is more stable than all the ot her tetrahedrane alternatives for C4H4. The triply hydrogen bridged st ructure 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 calculation s with the quasirelativistic pseudopotential basis set show the quadru ply 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 org anometallic chemistry are competitive for heavier elements (Si to Pb). The periodic behavior begins only with the second period; Li to Ne, a re the exceptions. Suggestions for the realization of these H-bridged structures for Pb from NaPb are discussed.