Two series of variously substituted tridentate Schiff-base ligands, namely salicylaldehyde pyridine-2'ylhydrazones (HL) and N-(pyridine-2 ylmethyl)salicylideneamines (HL), were synthesised and complexed with Fe", Cu" and Co.". The formulations of the former series of ligands were ascertained by elemental analyses and mass spectrometry, and the physical properties of these ligands were investigated using IR and 'H-NMR spectroscopy. However, the HL? series was produced in situ in template reactions. The X-ray crystal structures of the corresponding six-coordinate iron(III) complexes [FeL2]C104 [HL = HL' or H(3,5-Buz)-L') and (HL = HL-] show that the hetero donor Schiff-base ligands are tridentate, coordinating to the metal co meridionally through an imine nitrogen, a pyridyl nitrogen and a phenolate oxygen to give a trans, cis,cis-octahedral arrangement. For the hydrazone complexes ([FeL'2]C104 series), the bond distances in the coordination sphere of the iron(III) atom at 100 K point to the existence of the high-spin state. However, structural analysis has shown that for the analogous [FeL2]C104 series, at 150 K there is co existence of both the high-spin and low-spin states in the same unit cell. Interestingly, in solution, both series of iron(III) complexes undergo a 41 42T2 interconversion, as evidenced by variable-temperature EPR spectroscopy. For [FeL22]C104, in MeOH/EtOH (3:1, v/v) the spin transition appears to be gradual (with Tc-150 K) whereas in the case of [FeL2]C104 the spin-crossover is abrupt. Turning to copper(II), the complexes of this metal ion with the hydrazone ligands are dinuclear and are of the general formula (Cul (O2CCH3)]2. Crystallographic analysis of [Cu(3,5-Br2 -L'OCCH3)2 has revealed a centrosymmetric dimeric structure with a distorted square pyramidal geometry (t = 0.167) at each metal centre. The metal ked via acetato bridges, each adopting an unusual monodentate coordination mode. EPR spectroscopy has indicated that in strongly coordinating solvents such as MeOH and EtOH, the Cu" dimers dissociate to form monomeric species. Finally, cobalt(II) complexes with both the HL' and HL2 series of Schiff-base ligands were isolated and characterised by spectroscopy and X-ray crystallography. The crystal structure of [Co{(3,5-Buz)-L'}2]Br.EtOH confirmed the expected meridional arrangement of the tridentate ligands and the trans, cis,cis-coordination of the donor atoms. Electronic spectroscopy showed one of the two spin-allowed ligand-field transitions: 'Alg → Tig. The higher-energy d-d band is thought to coincide with the intense absorption of the Pe - do* charge-transfer transition arising from the interaction of the phenolate oxygen with the cobalt(III) ion. The electronic spectra are consistent with the low-spin do configuration of the cobalt(III) ion