ENTHALPY AND ENTROPY OF SUBLIMATION OF TETRAPHENYLTIN AND HEXAPHENYLDITIN . BOND DISSOCIATION ENERGY OF SN-C AND SN-SN

The vapor pressures of solid tetraphenyltin and hexaphenylditin have been measured directly by measurements of the torsional recoil of a suspended effusion cell, Pτ, and indirectly by measurement of the mass effusion, PΚ. The results of the sublimation pressures in atmospheres are: For tetraphenyltin the torsional recoil yields in the range 428-454°K log10 P = (12.942 ± 0.753) - (7963 ± 33)T-1; the mass effusion yields in the range 393-461°K log10 PΚ = (12.816 ± 0.131) - (7927 ± 56)T-1. For hexaphenylditin the torsional recoil yields in the range 463-503°K log10 P = (14.087 ± 0.276) - (9373 ± 42)T-1; the mass effusion yields in the range 444-503°K log10 PΚ = (14.082 ± 0.124) - (9399 ± 59)T-1. The cited errors are standard deviations generated in the least-squares analyses. The average ratio Pτ/PΚ is of the order of 1.10; the deviation from unity represents a systematic difference between the two procedures. The enthalpies and entropies of sublimation derived from the measurements are 36.3 ± 0.3 kcal mol-1 and 58.6 ± 0.6 eu for tetraphenyltin at 433°K and 43.0 ± 0.3 kcal mol-1 and 64.4 ± 0.6 eu for hexaphenylditin at 475°K, respectively. The average bond dissociation energy, Ē(Sn-C) is calculated to be 55.8 ± 1.7 kcal mol-1, and the bond dissociation energy of Sn-Sn in hexaphenylditin is calculated to be 36.3 ± 2.4 kcal mol-1.