Electron acceptor–electron donor interactions. Part XX. Charge-transfer interactions of some of the highest-valency halides, oxyhalides, and oxides with aromatic hydrocarbons and fluorocarbons. Ball–plane interactions. Group VB

Abstract

We examine the species NF₃O, PF₅, PF₃O, PCl₅, PCl₃O, AsF₅, SbCl₅, and SbF₅. Both phosphorus and antimony pentachlorides, particularly the latter, are reactive and impose restrictions on the choice of donors for equilibrium studies. Nevertheless, phosphorus pentachloride with naphthalene and antimony pentachloride with benzene and octafluoronaphthalene demonstrate intermolecular spectra and exhibit extremely weak 1:1 interactions in a number of solvents; moreover the naphthalene–phosphorus pentachloride system is thermochromic. Phosphoryl chloride behaves like carbon tetrachloride in that it enhances markedly the spectra of hexamethylbenzene in solution (less so for benzene, naphthalene, anthracene, and pyrene) and this characterizes an extremely weak or just contact 1:1 interaction. The transition is assigned tentatively to a combined intensity-borrowing and electron-transfer process. Intermolecular charge-transfer spectra are not observed with other compounds of Group VB, although some of the materials are reactive chemically. Attempts at detecting arsenic and bismuth pentachlorides are unsuccessful. A spectrophotometric method for determining molecular self-association is suggested and it is pointed out that continuous-variation plots for a weakly interacting system do not provide information on molecularity.