Coordinative versatility of 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline ( L) to different metal ions: syntheses, crystal structures and properties of [Cu(I) L] 2 2+ and [M L] 2+ (M=Cu(II), Ni(II), Zn(II) and Co(II))

Abstract

Listen

Translate article

The complexes of Cu(I), Cu(II), Ni(II), Zn(II) and Co(II) with a new polypyridyl ligand, 2,3-bis(2-pyridyl)-5,8-dimethoxyquinoxaline ( L), have been synthesized and characterized. The crystal structures of these complexes have been elucidated by X-ray diffraction analyses and three types of coordination modes for L were found to exist in them. In the dinuclear complex [Cu(I) L(CH 3CN)] 2·(ClO 4) 2 ( 1), L acts as a tridentate ligand with two Cu(I) centers bridged by two L ligands to form a box-like dimeric structure, in which each Cu(I) ion is penta-coordinated with three nitrogen atoms and a methoxyl oxygen atom of two L ligands, and an acetonitrile. In [Cu(II) L(NO 3) 2]·CH 3CN 2, the Cu(II) center is coordinated to the two nitrogen atoms of the two pyridine rings of L which acts as a bidentate ligand. The structures of [Ni(II) L(NO 3)(H 2O) 2]·2CH 3CN·NO 3 ( 3), [Zn(II) L(NO 3) 2 (H 2O)]·2CH 3CN ( 4) and [Co(II) LCl 2(H 2O)] ( 5) are similar to each other in which L acts as a tridentate ligand by using its half side, and the metal centers are coordinated to a methoxyl oxygen atom and two bipyridine nitrogen atoms of L in the same side. The formation of infinite quasi-one-dimensional chains ( 1, 4 and 5) or a quasi-two-dimensional sheet ( 2) assisted by the intra- or intermolecular face-to-face aryl stacking interactions and hydrogen bonds may have stabilized the crystals of these complexes. Luminescence studies showed that 1 exhibits broad, structureless emissions at 420 nm in the solid state and at 450 nm in frozen alcohol frozen glasses at 77 K. Cyclic voltammetric studies of 1 show the presence of an irreversible metal-centered reduction wave at approximately −0.973 V versus Fc +/0 and a quasi-reversible ligand-centered reduction couple at approximately −1.996 V versus Fc +/0. The solution behaviors of these complexes have been further studied by UV–Vis and ESR techniques.