Cobalt(II), copper(II), zinc(II) and cadmium(II) complexes based on dibenzimidazolyl bidentate ligands with alkanyl linkers: crystal structure, weak interactions and conformations

Eight metal complexes, {[Co(bibim-4)(2)(H2O)(2)](NO3)(2)}(n) (1), {[Cu(bibim-4)(2)(NO3)](NO3)}(n) (2), [Co(bibim-3)(TP)](n) (3), [Zn-2(bibim-3)](2)(OAc)(4)] (4), [Co(bibim-2)(NO3)(2)](n) (5), [Zn(bibim-4)(NO3)(2)](n) (6), [Zn(bibim-4)(OAc)(2)](n) (7) and [Cd(bibim-4)(NO3)(2)(DMF)](n) (8) (bibim-2 = 1,2-bis(benzimidazol-l-yl)ethane, bibim-3 = 1,3-bis(benzimidazol-l-yl)propane, bibim-4 = 1,4-bis(benzimidazol-l-yl)butane and TP = terephthalate) have been prepared by means of the self-assembly of Co(II), Cu(II), Zn(II) or Cd(II) salts, dibenzimidazolyl bidentate ligands bearing alkanyl linkers and terephthalic acid. These complexes are structurally characterized by X-ray diffraction analyses. In complexes 1 and 2, 2D network layers with macrometallocycles are formed via metal centers and the ligand bibim-4. A 2D network layer with macrometallocycles in 3 is formed via Co(II) centers, the ligand bibim-3 and terephthalate molecules. In complex 4, a 20-membered macrometallocycle is formed by two bibim-3 ligands and two Zn(II) atoms. In complexes 5-8, 1D polymeric chains are formed via metal centers and the bibim-2 or bibim-4 ligands. In the crystal packings of complexes 1-8, 2D supramolecular layers and 3D supramolecular frameworks are formed via intermolecular weak interactions, including pi-pi interactions and hydrogen bonds. The different types of pi-pi interactions from the benzimidazole ring as well as the conformations of the ligands and metal complexes are described. Additionally, the fluorescence emission spectra of the ligands and metal complexes are reported.