Phosphorus-31 and selenium-77 nuclear magnetic resonance spectra of phosphorus-poor phosphorous selenide compounds

Abstract

The compounds P₃Se₄X (X = I, Br, Cl, SC₂H₅, SC₅H₁₁ or SC₆H₅) have been made as phosphorus-poor analogues of the corresponding compounds α- or β-P₄E₃X₂(E = S or Se), in which a PX unit has been replaced by Se. Analysis of ³¹P and (in part)⁷⁷Se NMR spectra of the P₃Se₄X compounds has shown remarkable correspondence of the coupling constants and chemical shifts between the P₃Se₄X and α-P₄S₃X₂ series of compounds. Phosphorus-31 and ⁷⁷Se NMR spectra of α-P₄Se₃I₂ are reported for comparison. Further replacement of a PX unit by Se gives the ultimate phosphorus-poor cluster compound P₂Se₅, for which a synthesis from the elements and full NMR data are reported. This sought after higher selenide of phosphorus is thus a phosphorus-poor molecule with concatenated selenium, rather than a selenium-rich structure with exocyclic selenium. The interconversion of optical isomers of the P₃Se₄X halides (X = I, Br or Cl), by skeletal rearrangement on the NMR time-scale, has been studied at several temperatures, yielding kinetic data.