The coordination chemistry of various transition metal halides and carbonyl compounds has been investigated from several viewpoints. The coordination behaviour of 1,3,2,4 diazadiphosphetidines exemplified by(ClPNBut)2, towards metal halides and carbonyls has been studied. Novel metal complexes incorporating the four-membered ring system as a bidentate P-donor have been characterized. Both bridging and chelating behaviour was observed. From the reactions of Fe2(CO)9 with the potentially tetradentate N-donors, TREN, Me6TREN and TRIFN, both mono-and bi-nuclear complexes have been isolated. However in all cases the ligand appeared to be denyea a tetradentate mode of attachment. For the MC13/NME(M:=Ti,V and Cr) systems, a second, monoadduct was identified for each case, namely [MC12NME3](M=Ti,Cr)and[VCl3NMe3]. The reactions of (C5H5)2Ti(Set)2 with [MC13(THF)3] M=Ti,V and Cr) have been studied in a preliminary investigation into possible routes to mixed-valence compounds. From the evidence collected we find that ligand exchange occurs rather than formation of the desired mixed-valence species. As a result of collaboration with Nairobi University, the reactions of thiourea with the group VB trihalides have been investigated. Spectral data provided evidence for coordination of thiourea via the sulphur atom in all complexes except the PCI, case, for which unambiguous characterization was not achieved. A further study of the antimony complexes as possible schistosomicides is being carried out at Nairobi University.