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

Abstract

Vanadium oxytrichloride, pentafluoride, and oxytrifluoride, and niobium and tantalum pentachlorides, oxytrichlorides, and pentafluorides are examined. Intermolecular charge-transfer spectra are established for aromatic hydrocarbons or fluorocarbons with vanadium oxytrichloride, niobium and tantalum pentachlorides, and possibly in one case vanadium pentafluoride. The vanadium oxytrichloride interactions are extremely weak or just contact in terms of equilibrium measurements for the solvents cyclohexane and carbon tetrachloride, and in terms of the effect of temperature on the benzene and naphthalene spectra. Thermochromism, namely coloured liquids that freeze to solids the colour of the components, occurs for vanadium oxytrichloride and tantalum pentachloride with benzene and octafluoronaphthalene. Equilibrium constants for the niobium and tantalum pentachloride interactions also show them to be very weak, although the derived enthalpies, ca. 1·5 kcal mol^–1, though small, are the largest in this series of papers. It is speculated that the extended dimer structures may afford more favourable conditions for molecular association. The remaining halides and oxyhalides do not show intermolecular spectra, but in some cases react chemically. For comparable molecular species, increasing electron affinities occur in the order Ta < Nb < V.