Work on iron mononitrosyl complexes of bidentate Schiff base anions derived from salicylaldehyde is described. The complex bis(N-benzylsalicylideneiminato)nitrosyliron and its 4-methyl and 4-methoxy derivatives are the first examples of such compounds to be synthesised. The magnetic properties over the temperature range 293 to 87 K show that they are high spin {FeNO}7 with slightly temperature dependent effective magnetic moments. Infrared investigations suggest that the Fe-N-O groups are linear. Attempts to prepare an iron mononitrosyl with Schiff base derived from 2-hydroxyacetophenone and ethylenediamine resulted in the formation of a binuclear iron(III) oxo-bridged complex, mu-oxo-bis[N,N'-bis(2-hydroxyaceto-phenone)ethylenediiminato]iron(III)], which, when investigated by X-ray crystallography, is shown to contain a bent bridging group with a Fe-O-Fe bond angle of 156.7. This is the first example of au-oxo iron(III) complex with a 2-hydroxyacetophenone-derived Schiff base. A series of cobalt mononitrosyls, mainly with bidentate Schiff base coligands derived from salicylaldehyde has been prepared and characterized by infrared, 1H, 15N and 59Co NMR spectroscopies as well as magnetic measurements. The infrared and 15N NMR indicate that the Co-N-O groups in these complexes are bent. Cobalt(II) complexes of the macrocycle 6,13-diphenyl-1,8-dihydro-2,3:9,10-dibenzo-1,4,8,11-tetraaza-cyclotetradecane-4,6,11,13-tetraene (dptaaH2) and its methyl, methoxy, bromo and nitro derivatives have been prepared. On reaction with nitric oxide, they form mononitrosyls. Similar investigations show that the Co-N-O groups are bent and this has been confirmed by an X-ray investigation carried out on Co(dptaa)NO from which the Co-N-O bond angle is 122.6°. All the mononitrosyls show temperature independent paramagnetism with fractional magnetic moments at room temperature in the range 0.59-1.31 B.M. X-ray investigations carried out on two cobalt(II) Schiff base complexes, bis(N-n-butylsalicylideneiminato)cobalt(II) and bis(N-t-butylsalicylidene-iminato)cobalt(III), suggest that the unreactivity of the t-butyl derivative to nitric oxide and dioxygen in contrast to the n-butyl derivative is due to steric hindrance of the t-butyl group. The reactivity of Co(dptaa) towards chloroform, Br2 and I2 was investigated in attempts to prepare complexes of the type Co(dptaa)X where X = Cl, Br and I. Although reasonable microanalyses were obtained, the magnetic moments of the chloride and bromide were higher than expected for cobalt(III) complexes. Unfortunately, they could not be recrystallised to remove possible paramagnetic impurities. Several chromium(II) complexes of Schiff bases derived from 2-hydroxyacetophenone have been prepared via the sodium and lithium salts of the bases. The instability of the complexes has however, prevented complete characterization. Some miscellaneous investigations, mainly of chromium(ll) complexes are also reported.