An industrial problem concerning a pesticide product, ®Tinox, lead to the work described in this thesis. This included the study of the chelating properties of six sulphur and oxygen ligands and five phosphoryl sulphur and oxygen ligands with nickel(ll) and coba lt(ll) halides. Thirty two complexes of nickel(II) and cobalt(ll) halides were prepared and are reported in this thesis. The ligands used in the investigation are 1. 3-thiabutanol 2. 1-mereapto-3-thiabutane 3. 1-mereapto-2-methoxyethane 4. l-methoxy-3-thiabutane 5. Di-(2-inethylthioethyl) disulphide 6. Di-(2-methoxyethyl) disulphide 7. 0,0-dimethyl methyl phosphorodithioate 8. 0 0, 0-dimethyl (2-methylthioethyl) phosphorodithioate 9. 0,0-dimethyl 0-(2-methylthioethyl) phosphorothionate 10. 0,0-dimethyl S-(2-methylthioethyl) phosphorothiolate 11. 0,0-dimethyl (2-methylthioethyl) thiophosphonate The complexes were investigated by magnetic, spectrophotometric (infrared, ultraviolet) and conductiometric measurements. The stereochemistry of the complexes prepared depended on the particular ligand used and examples of octahedral tetrahedral and square planar complexes of nickel (ll) halites and tetrahedral and square planar of cobalt halides complexes were obtained. A comparison between the co-ordinating properties of sulphur and oxygen in their analogout forms i.e. thiol with hydroxyl, thioether with ether and thiophosphate with phosphate was made. A preliminary study on the use of ferric salt in the stablisation of ®Tinox was conducted. No conclusion could be established at this stage and further experimental work is required for a proper evaluation on the potential use of the ferric salt.