Molecular structures of monomeric gallium trichloride, indium trichloride and lead tetrachloride by gas electron diffraction

Abstract

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 D_3h symmetry and bond distances r_a= 210.8(3) and 228.9(5) pm respectively. The data for PbCl₄ are consistent with an equilibrium structure of T_d symmetry and r_a= 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.