Unstable intermediates. Part CLX. An electron spin resonance study of PCl4, PCl5–, PCl62–, and PCl6 radicals in irradiated phosphorus pentachloride

Abstract

Exposure of phosphorus pentachloride (PCl₄⁺ PCl₆^–) to ⁶⁰Co γ-rays at 77 K gave PCl₄ and PCl₅^– radicals in comparable yields, together with a species thought to be PCl₆^2– in lower yield. The isotropic ³¹P hyperfine coupling increases in this order (ca. 1 310 G, 1 617 G, and 1 815 G respectively). At 77 K PCl₄ has two inequivalent chloride ligands (A_isoca. 35 G and 0 G respectively). The PCl₅^– species exhibited a smaller, poorly resolved, splitting interpreted as coupling to four equivalent chloride ligands. The species thought to be PCl₆^2– also exhibited a multiple splitting from several chloride ligands but overlap of features made accurate assessment impossible.

Similar spectra for PCl₄ and PCl₅^– radicals were obtained from solutions in carbon tetrachloride and toluene, in which PCl₅ molecules are present, but the outer features assigned to PCl₆^2– were absent.

Well resolved central features obtained from the pure material indicated hyperfine coupling to one phosphorus and two equvalent chlorine nuclei. This species is thought to be a strongly distorted PCl₆ radical.