Investigations on molecular complexes. Part 7.—Thermodynamic, spectroscopic and dielectric properties of iodine complexes with triphenylphosphine oxide, sulphide and selenide

Abstract

The increase in free energy (–ΔF) and entropy (–ΔH) of complex formation between iodine and triphenylphosphine oxide (TPPO), triphenylphosphine sulphide (TPPS) or triphenylphosphine selenide, respectively, parallels the enhancement of the transition dipole moments of both the charge transfer and visible iodine bands and also parallels the increase of dipole moment change on complex formation; the energy of the charge transfer transition decreases.

In contrast to other iodine–donor complexes, the blue shift of the visible iodine band is almost independent of strength of bonding in the complex. Assuming a reasonable structure for the complex, values of Δµ_ind and Δµ_CT have been evaluated. The contribution of a dative structure to the ground state wavefunction obtained from dipole moment data is in good agreement with that calculated from hν_CT and –ΔH values.