Synthesis and characterization of four coordination polymers constructed with d10 metals and mixed flexible ligands under solvothermal conditions

Solvothermal reactions of flexible 1,2-phenylenedioxydiacetic acid (H2PDA) or hydroquinone-O,O′-diacetic acid (H2QDA) with zinc nitrate or cadmium nitrate in the presence of auxiliary 1,1′-(1,4-butanediyl)bis(imidazole) (BBI) ligand gave rise to four coordination polymers, namely, {[Zn(PDA)(BBI)]·3H2O}n (1), {[Zn(PDA)(BBI)]·DMF}n (2), {[Cd2(QDA)(BBI)]·4H2O}n (3), [Cd(QDA)(BBI)]n (4). All the compounds were characterized by elemental analysis, IR and single-crystal X-ray diffraction methods. Compound 1 exhibits a puckered (2D) (4, 4) grid net with a Schlafli symbol of 44 62. Compound 2 has the dinuclear Zn2(PDA)2 “loops” which are further connected by BBI ligands into 2D sheet along (0 1 −1) plane with a Schlafli symbol of 2.65. Interestingly, the Zn2(PDA)2 “loops” are penetrated by BBI ligands of the other equivalent net. Thus an unusual 2D polyrotaxane-like structure is formed containing rotaxane-like motifs. Compound 3 possesses a three-dimensional (3D) diamond-type network with a Schlafli symbol of 66. Compound 4 has the dinuclear cadmium core as the node and shows a 3D threefold interpenetrating 8-connected uninodal network with a Schlafli symbol of 36418536. The structural differences of these complexes give some insights into the effect of solvent on the construction of coordination polymers with the same components under solvothermal conditions. In addition, the fluorescent properties of 1–4 were also investigated.