Structure and binding energies of EM6 clusters (E = C, Si, Ge Sn, Pb; M = Li, Na, K, Rb, Cs): PbNa6 is not unique

A computational study of twenty-four EM6 clusters is described (E = C, Si, Ge, Sn or Pb; M = Li, Na, K, Rb or Cs). Almost all are octahedral. Total binding energies, obtained at the DZP/QCISD(T) level of theory using pseudopotential method, range from 446 to 1108 kJ/mol and decrease as both E and M increase in size. Several EM4 and EM5 systems were also studied, together with PbNa7 and PbNa8. Loss of one M atom from EM6 requires more energy than from EM5. PbNa7 and PbNa8 are relatively weakly bound. Trends in structures and binding energies are analysed. PbNa6, detected by mass spectrometry [Chem. Phys. Letters 237 (1995) 334], is not unique either geometrically, thermodynamically, or for its electronic structure; possible relationships with CLi6 are discussed. The detection of many more EM6 clusters can be anticipated.