Cationic complexes of the type [Hg(phosphine)n](ClO4)2 (n = 2, 3, 4) (phosphine = P(t-Bu)3, PCy3, P(4-Me2NC6H4)3, P(4-MeOC6H4)3, P(4-MeC6H4)3, P(3-MeC6H4)3, P(2-MeC6H4)3, P(4-FC6H4)3, P(4-ClC6H4)3) have been prepared and studied by vibrational spectroscopy in the perchlorate and low frequency regions, as well as by 31P and 199Hg nmr. The skeletal Hg—P frequencies have been assigned in both solution and the solid state. It was found that 1J(Hg—P) decreases with increasing phosphine basicity and that it is also dependent upon sample concentration and temperature.