Cyclic inorganic compounds. Part VII. The mass spectra of the trimeric chlorobromophosphonitriles

Abstract

The electron impact behaviour of the non-geminally substituted cyclic chlorobromotriphosphonitriles, P₃N₃Cl_xBr_6–x′ is described. With the exception of the hexachloride, the parent ion is of low intensity and the base peak arises from loss of a bromine atom. Fragmentation to cyclic and linear ions similar to those described for P₃N₃Br₆ and P₃N₃Cl₆ occurs, but bromine atoms are preferentially lost. For all the compounds, approximately the same percentage of the positive ion current results from cyclic (∼72%) and linear (∼17%) ions. The effect of increased bromine content on the detailed ion current distribution within each of these series is discussed. The large decrease in ionization potential when one bromine atom is substituted into the hexachloride can be rationalized on the basis of increased localization of electron density on the ring nitrogen atoms. From appearance potential data, ΔH_f° for P₃N₃Cl₅Br is calculated as –168·6 kcal.mole^–1.