Vaporization of Li2C2(s) and thermochemical properties of gaseous CL3, CL4, and CL6

Vaporization of Li2C2(s) was examined by means of Knudsen-effusion mass spectrometry. From the equilibrium partial pressures of Li(g), Li2(g), CLi3(g), CLi4(g), and CLi6(g) observed at temperatures from 961 to 1168 K, the third-law values for atomization energies of CLi3(g), CLi4(g), and CLi6(g) were determined to be D0 (CLi3)=918±10, D0 (CLi4)=1149±24, and D0 (CLi6)=1529±28 kJ/mol. The corresponding average C-Li bond energy of these molecules were 306±10, 287±24, and 255±28 kJ/mol. The CLi6 molecule should be a hypervalent molecule, which had been theoretically predicted from ab initio molecular orbital calculation by Schleyer et al. The observed dissociation energy of CLi6 to form CLi4, 274±11 kJ/mol, agreed well with the theoretical value, 273 kJ/mol. The dissociation and atomization energies determined in this work indicate that the strong bonding must be present in the hyperlithiated CLi6 molecule. (orig.)