The ternary metal mixed ligand complexes formed by benzimidazole and N,N-bis( 2-hydroxyethyl) glycine

The stability constants of the ternary M(Bit)(Bzim)(+) complexes, where M2 = Cu2+, Ni2+ or Zn2+ Bic(-) = the anion of N, N-bis(2-hydroxyethyl) glycin e and Bzim = benzimidazole, were determined by potentiometric pH titration in aqueous solution. One of them (M2+ = Cu2+) was also separately determine d by spectrophotometry. The results show that these ternary complexes are s tabler than expected on statistical grounds. The enhanced stability of the ternary M(Bic) (Bzim)(+) complexes is attributed to the pi(A)-pi(B) coopera tive effect between Bic(-) and benzimidazole. Besides, compared with Cu(Bic ) (Bzim)(+) and Ni(Bic) (Bzim)(+), the ternary Zn(Bic) (Bzim)(+) complex ha s relatively high stability. The crystal structure of [Cu(Bic)(Bzim)] CiO(4 ) was determined by single crystal X-ray diffraction techniques. The copper atom has a trigonal-bipyramidal geometry, the basal plane is formed by an oxygen atom of the carboxylato group and two hydroxyl oxygen atoms, the api cal position is occupied by a nitrogen atom of Bic(-) and a nitrogen atom o f benzimidazole. The molecular structure of Cu(Bic) (Bzim)(+) in aqueous so lution is different from that in the crystalline state. The results of ESR and electronic spectra show that the structure of this complex is octahedro n in aqueous solution.