Mixed ligands/Coordinate complexes are still largely investigated. This is because of their very wide range of uses and applications.The mixed ligand complexes of Co (II) and Ni (II) with hippuric acid, ammonium thiocyanate and hydroxyl ammonium chloride were synthesized in a 1:2:2:2 stoichiometric ratio by a modified direct combination method. The resulting complexes were characterized by preliminary tests and spectroscopic methods. The physicochemical parameters such as melting point, boiling point, pH, electrical conductivity and colour of the complexes were determined. The solubility in water, ethanol, and methanol were also studied at 25oC. The characterization of the prepared mixed-ligand complexes was done using FT-IR, UV-VIS, XRD, crystallography and XRF spectroscopic methods. The percentage yield obtained were 42.90% and 40.70% Co (II) and Ni(II) complexes respectively. Both complexes were soluble in methanol, but slightly soluble in water and ethanol at 25oC.This implies that the ionic complexes formed are generally polar, since they are quite soluble in polar solvents such as water, ethanol and methanol. The complexes were acidic with pH values of 3.24 and 3.30 for Co(II) and Ni(II) respectively. The melting and boiling points of the complexes were (190 and 206)oC and (50 and 80.2)oC for Co(II) and Ni(II) respectively. The low melting and boiling points of the synthesized complexes may be due to the nature of the bond in the complexes since they are not completely ionic and possibly the properties of the central metals. The electrical conductivities were found to be (1.2 x 10-1 and 1.1 x 10-1 ) ᶙs/cm for Co(II) and Ni(II) complexes. This indicates that the complexes are non-electrolytes. Elemental analysis corresponds to metal: ligand stoichiometry for Co (II) and Ni II) complexes are

Keywords : Co (II) and Ni (II) complexes; Synthesis; Characterization; Crystallography; spectroscopy;Mixed ligands.