Crystal engineering of cadmium coordination polymers decorated with nitro-functionalized thiophene-2,5-dicarboxylate and structurally related bis(imidazole) ligands with varying flexibility

Abstract

A new thiophene-2,5-dicarboxylic acid derivative, 3-nitro-thiophene-2,5-dicarboxylic acid (H₂ntdc), was synthesized. Reaction of H₂ntdc with cadmium diacetate dihydrate and structurally related bis(imidazole) ligands with varying flexibility gave rise to four new CPs, formulated as {[Cd(ntdc)(bmip)(H₂O)](H₂O)}_n (1), {[Cd(ntdc)(bmib)](H₂O)}_n (2), [Cd(ntdc)(beip)]_n (3) and [Cd(ntdc)(beib)]_n (4) [bmip = 1,3-bis(2-methylimidazolyl)propane, bmib = 1,4-bis(2-methylimidazolyl)butane, beip = 1,3-bis(2-ethylimidazolyl)propane and beib = 1,4-bis(2-ethylimidazolyl)butane]. Moreover, a new compound {[Cd(ntc)₂(bmib)](H₂O)}_n (5) (Hntc = 4-nitro-thiophene-2-carboxylic acid) involving in situ ligand synthesis was prepared. Structural analyses reveal that 1 features a two-dimensional (2D) 4⁴-sql layer, and is further stacked via hydrogen bonding interactions to give a three-dimensional (3D) hydrogen-bonded architecture. 2 displays a 3,4-connected 3D network with ins type topology, which is composed of 2D hcb topological networks pillared by the bmib ligands. 3 exhibits a 3,5-connected 3D network with a (4²·6³·8⁵)(4²·6) topology. 4 possesses a 3-fold interpenetrating 3D net with a dmp topology. 5 can be described as a one-dimensional (1D) chain structure, and is further assembled into a 2D hydrogen-bonded 4⁴sql layer. Factors that influence the structural assembly of 1–4, as well as the formation of 5 involving the in situ produced Hntc ligand, are discussed. Moreover, structure stabilities and photoluminescence properties of the complexes were also investigated.