Molecular structures of monomeric gallium trichloride, indium trichloride and lead tetrachloride by gas electron diffraction
Gas electron diffraction data for monomeric GaCl3, monomeric InCl3 and PbCl4 have been recorded with nozzle temperatures of about 380, 480 and 20 °C respectively. The data for GaCl3 and InCl3 are consistent with equilibrium structures of D3h symmetry and bond distances ra= 210.8(3) and 228.9(5) pm respectively. The data for PbCl4 are consistent with an equilibrium structure of Td symmetry and ra= 237.3(3) pm. Bond energies and distances from the literature show that the M–Cl bonds in MCl(g) are stronger, but longer, than in MCl3(g) for M = Al, Ga or In, and that M–Cl bonds in MCl2(g) are stronger, but longer, than in MCl4(g) for M = Ge, Sn or Pb. It is suggested that the relative weakness of the bonds in group-valent chlorides is due to the energy required to promote the Group 13 metal atoms from the 2P (s2p) ground states to 4P(sp2) valence states, or to promote the Group 14 metal atoms from 3P(s2p2) ground states to 5S(sp3) valence states. Further that the decreasing stability of the group-valent relative to subvalent chlorides as the Groups are descended is due both to increasing promotional energies and to decreasing M–Cl bond strengths.