Investigation of the structure variation of metal diphosphonates with the changing of N-donor auxiliary ligands and their properties

Abstract

Nine metal diphosphonates, [Co(H2L)(pyz)(H2O)][(H2O)0.3] (1), [Ni(H2L)(pyz)(H2O)2] (2), [Ni(H2L)(2,2′-bipy)2][(H2O)2] (3), [Ni(H2L)(4,4′-bipy)(H2O)][(H2O)2] (4), [Ni(H2L)(dpe)(H2O)2][(H2O)2] (5), [Cu(H2L)(pyz)(H2O)2] (6), [Cu(H2L)(4,4′-bipy)][(H2O)2] (7), [Zn(H2L)(2,2′-bipy)(H2O)2] (8) and [Cd(H2L)(pyz)(H2O)2] (9), have been synthesized from a diphosphonate ligand 2,5-dimethyl-1,4-phenylenediphosphonic acid (H4L) and four N-donor auxiliary ligands (pyz = pyrazine, 2,2′-bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine, dpe = 1,2-di(4-pyridyl)ethylene). In compound 1, pyrazine molecules behave as pillars which connect the Co(H2L) layers into a 3D network structure. Compounds 2, 6 and 9 are isostructural and also show 3D framework structures, in which metal centers are linked by the bidentate diphosphonate ligands into 1D infinite chains and are connected by the pyrazine linkers. In compounds 3 and 8, the diphosphonate ligands, showing bidentate or tetradentate coordination modes, bridge the respective metal ions (Ni2+ and Zn2+) into a 1D infinite chain or 2D layer structure, respectively, in which the 2,2′-bipy ligands chelate to the central metal ions and complete the coordination spheres. In compound 4, the 4,4′-bipy molecules also behave as pillars between the 2D layers, which are constructed from tridentate bridging diphosphonate ligands and six-coordinated Ni2+ ions. Compounds 5 and 7 have similar square grid layered structures which are constructed from bridging bidentate diphosphonate ligands and 4,4′-bipy or dpe linkers. Photophysical measurements indicate that compounds 8 and 9 display ligand centered emissions. Magnetic studies reveal that dominant antiferromagnetic interactions are propagated in compounds 1–3 between the magnetic centers.