Self-assembled coordination polymers of Zn(II): syntheses, structural diversity, luminescence properties and base catalysis

Abstract

Two new Zn(II) metal–organic networks, {[Zn(m1-muco)(4bpdh)(H2O)] H2O} (1) and {[Zn2(m3-muco)2(m- 3bpdb)2(H2O)] 6H2O}n (2) (where, muco = trans,trans-muconate dianion, 4bpdh = 2,5-bis(4-pyridyl)-3,4- diaza-2,4-hexadiene and 3bpdb = 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene) were synthesized at room temperature. Single-crystal X-ray structural determination revealed that compound 1 possesses a 1D coordination polymeric chain extended to a 3D supramolecular framework via (HAO H and OAH N) hydrogen bonding interactions and compound 2 has a 3D pillar-layered framework with 7- connected, {33 47 58 63} net topology. Photoluminescence measurements of 1 and 2 showed ligand based emissions owing to intra ligand and/or ligand to ligand charge transfer {(p⁄?n and p⁄?p)} transitions. The thermal stabilities of the compounds 1 and 2 were also examined. Application of the compounds as heterogeneous catalysts for the Knoevenagel reaction showed higher catalytic activity of 2 over 1 which has been ascribed to the presence of exposed basic azine (AC@NA) groups in the 1D channels of 2. The catalyst can be easily separated from the reaction mixture and reused for five cycles without significant loss in the catalytic activity. Herein, the influence of ancillary ligands on the structural and catalytic properties of two new Zn(II)–organic networks 1 and 2 has been presented.