Phosphorus-31 and selenium-77 nuclear magnetic resonance spectra of sulphur- or arsenic-substituted derivatives of tetraphosphorus triselenide; fitting of chemical shifts and coupling constants to molecular parameters for cage compounds containing a phosphorus–selenium–phosphorus linkage

Abstract

Phosphorus-31 and selenium-77 n.m.r. spectra have been measured and assigned to give chemical shifts and coupling constants for PP₃S₂Se (1), PP₃SSe₂(2), PP₂AsSe₃(4), PPAs₂Se₃(5), PAs₃Se₃(6), AsP₃Se₃(7), AsP₂AsSe₃(8), and AsPAs₂Se₃(9), where the symbol written first in each formula represents the apical phosphorus or arsenic atom. In each case, the presence of ⁷⁷Se in natural abundance allowed the molecule without ⁷⁷Se, and molecules with one ⁷⁷Se atom, to be studied. For molecules containing both basal phosphorus and basal arsenic atoms, spectra were seen of isotopomers with the ⁷⁷Se atom connected either to basal phosphorus [(4b), (5b), (8b), and (9b)] or to basal arsenic [(4c), (5c), (8c), and (9c)]. Complete chemical shift and coupling data were thus obtained for, inter alia, five molecules [(1b), (2b), (3b), (4b), and (5b)] containing a ³¹P–⁷⁷Se–³¹P linkage; the three shifts and three couplings which characterise this linkage could be fitted statistically by linear relationships involving two molecular parameters. Multiple regression analysis showed that two other coupling constants involving the basal phosphorus atom P_Acould be fitted to these same molecular parameters.