Complexes of functionalised phosphine ligands. Part 1. Complexes of FeIII, CoIII, NiII and ReV with tridentate Schiff bases having PNO, NNO and NNS donor sets. Crystal structures of 2-(Ph2PC6H4NCH)C6H4OH and [Co{2-(Ph2PC6H4CHN)C6H4O}2][PF6]