A novel Schiff base (H2L) derived from 1-phenyl-3-methyl-4-naphthylaceto-4,5-dihydropyra- zol-5-one (PMNAP) and 2-aminobenzimidazole (2-AB), and its copper, lead, nickel and cobalt complexes have been synthesized in the nonaqueous solvent. The formula of the four complexes was confirmed to be ML•H2O based on the elemental analysis, complexometric titration and mass spectral data. Their molecular structures were characterized by IR, UV, TG and 1H NMR. Moreover, an analytical method of the synthetic system of complexes by HPLC-MS was developed and three coexisting isomers of the ligand and its complexes and their corresponding MS data were observed on line. The integrated analytical results show that the novel ligand coexists in ketoform and enolform structures under the measuring conditions, the ketoform structure may change into the enolform structure during the coordination and bonds with the central ion by two O atoms of the enolized hydroxyl group of pyrazolone ring and H2O and the N atom of the imine group and the N atom containing H of benzimidazole ring by losing the proton. And the coordination number of these complexes is four.

Key words: HPLC-MS, synthesis, transitional metal complex, characterizati, Schiff base