Equilibrium studies on mixed ligand complex formation of Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-hydroxybenzyl)- l-histidine (H 2hb- l-his) and typical N,N donor ligands: Crystal structure of [Ni(hb- l-his)(bipyridine)] · H 2O complex

• Published in: Inorganica Chimica Acta Vol. 359; no. 10; pp. 3243 - 3251
• Main Authors: Bandyopadhyay, Susmita, Mukherjee, G.N., Drew, M.G.B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2006
• Subjects: Crystal structure; Metal(II) complexes; N-(2-hydroxybenzyl)- l-histidine; Stability constants; N-(2-hydroxybenzyl)- l-histidine; Stability constants; Metal(II) complexes; Crystal structure
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2006.03.031

N-(2-hydroxybenzyl)- l-histidine (H 2L) can discriminate Cu(II) from other 3d M(II) ions (M = Co, Ni and Zn) in binary [M(L)], [M(L) 2] 2−, [M 2(L)] 2+, [M 2(H −1L)] + and mixed ligand [M(L)(N,N)], [(N,N)M(H −1L)M(N,N)] + complexes (N,N = bipyridine, 1,10 phenanthroline and ethylenediamine). N 1–H deprotonated imidazolate moiety of the coordinate ligand offers bridging bidentate (N,N −) coordination to M(II) ions in the dinuclear [(N,N)M(H −1L)M(N,N)] + complexes. Equilibrium study on complex formation of Co(II), Ni(II), Cu(II) and Zn(II), hereafter M(II), with the quadridentate (O −, N, O −, N) donor ligand, N-(2-hydroxybenzyl)- l-histidine (H 2hb- l-his, hereafter H 2L), in the absence and in the presence of typical (N, N) donor bidentate ligands, 1,10 phenanthroline(phen), 2, 2′-bipyridine(bipy), ethylenediamine(en), hereafter B, in aqueous solution at 25 ± 1 °C was done at a fixed ionic strength, I = 0.1 mol dm −3(NaNO 3) by combined pH-metric, UV–Vis and EPR measurements provide evidence for the formation of mononuclear and dinuclear binary and mixed ligand complexes of the types: M(L), M ( L ) 2 2 - , M 2(L) 2+, M 2(H −1L) +, M(L)(B), (B)M(H −1L)M(B) +. The imidazole moiety of the ligand is found to act as a bridging bidentate ligand in the dinuclear M 2(L) 2+, M 2(H −1L) + and (B)M(H −1L)M(B) + complexes, using its N 3 atom and N 1–H deprotonated moiety. Stability constants of the complexes provide evidence of discrimination of Cu(II) from the other M(II) ions by this ligand. Solid complexes: [Ni(L)(H 2O) 2] ( 1), [Cu(L)(H 2O)] ( 2), and [Ni(L)(bipy)] · H 2O ( 3) have been isolated and characterized by various physicochemical studies. Single crystal X-ray diffraction of the ternary complex, 3, shows an octahedral [(O −,N,N,O −)(N,N)] geometry with extensive π–π stacking of the aromatic rings and H-bonding with imidazole (N 1–H), secondary amino N-atom, the lattice H 2O molecule, and the carboxylate and phenolate O-atoms.