Synthesis and Spectroscopic Studies of 4-butanoyl-3-methyl-1-phenylpyrazol-5-one and its Manganese (II), Lanthanum (III), Zirconium (III), Vanadium (V) and Tungsten (VI) Complexes

This study is aimed at the preparation of 4-butanoyl-3-methyl-1-phenylpyrazol-5-one (HBPy) by the acylation of 3-methyl-1-phenylpyrazol-5-one with butanoyl chloride; and the metal complexes of the HBPy with Mn (II), La (III), Zr (III), V (V) and W (VI) ions. Characterization was done by elemental analysis, UV-visible, IR and conductivity measurements. Physical properties such as colour, melting points and solubility profile were also determined for both the ligand and the complexes prepared. The results show that the ligand and the metal ions formed neutral complexes of the general formula, M (BPy) n. X (where M = metal ion, BPy = the ligand anion; X = an adduct and n = number of ligand molecules that complexed to M) ; in which Mn (II) formed dihydrate bischelate, Mn (BPy) 2.2H2O; V (V) formed a dioxo adduct bischelate of the type, VO2 (BPy). HBPy; W (VI) forms the dioxoaquo-bischelate, WO2 (BPy) 2. H2O; while La (III) and Zr (III) formed dihydrated trischelate, La (BPy) 3.2H2O and Zr (BPy) 3.2H2O respectively. The ligand complexed through its keto oxygen and/ or the deprotonation of the enolic hydrogen in its keto-enol tautomer. The CO-M bond stretching frequencies of the metal complexes were compared and the result showed that, in general, the bond increases with a decrease in the reduced masses of the oxygen and metal ions bonded. The ligand and its metal complexes studied are not ionic in nature. The complexes, Mn (BPy) 2.2H2O; La (BPy) 3.2H2O and Zr (BPy) 3.2H2O have been assigned octahedral while VO2 (BPy). HBPy and WO2 (BPy) 2. H2O have pentagonal bipyramidal geometries. The solubility data show that the complexes are soluble in many of the organic solvents having lone pair of electrons; hence, these solvents can be used with other inert organic solvents such as chloroform (CH3Cl) and carbon tetrachloride (CCl4) as solvent mixtures for extraction of the metal ions from their aqueous solutions.