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The He(I) photoelectron spectra of the title compounds have been measured. An empirical assignment of most of the bands is proposed and the effects of various substituents on the phosphorus lone-pair ionisation potentials are assessed. Correlations are made with various other parameters relating to phosphine basicity, and it is concluded that the phosphorus lone-pair i.p. provides a reasonable measure of relative basicity or σ-donor ability within related series of compounds.

Di-(t-butyl)fluorophosphine forms stable complexes of the type NiX2L2 and CoX2L2(where X = Cl, Br, or I and L = But2PF) with nickel(II) and cobalt(II) halides. The structure of these compounds, elucidated by n.m.r., i.r., and u.v. spectra as well as by magnetic measurements is trans-square planar in the case of NiX2L2 and tetrahedral for the complexes CoX2L2. For NiCl2(But2PF)2 a cis-trans-equilibrium is likely to exist in solution. The low-temperature 19F n.m.r. spectrum of the latter compound is explained by the presence of different rotamers with respect to the Ni–P axis.