Three-Dimensional Cd(II) Coordination Polymers Based on Semirigid Bis(Methylbenzimidazole) and Aromatic Polycarboxylates: Syntheses, Topological Structures and Photoluminescent Properties

To systematically explore the influence of aromatic polycarboxylate coligands on building high-dimensional Cd(II)-bmb (1,4-bis(2-methylbenzimidazol-1-ylmethyl) benzene) coordination polymers, we synthesized six coordination polymers, namely {[Cd(bmb)(o-phda)]·H2O}n (1), [Cd(bmb)0.5(m-phda)]n (2), [Cd(bmb)(p-phda)]n (3), [Cd(bmb)0.5(oba)]n (4), [Cd(bmb)(bpdc)]n (5), [Cd2(bmb)(bta)(mta)0.5]n (6), (H2phda = phenylenediacetic acid, H2oba =4,4′-oxybis(benzoic acid), H2bpdc = biphenyl-4,4′-dicarboxylic acid, H3bta =1,2,4-benzenetricarboxylic acid, and H2mta = 2-(methoxycabonyl)terephthalic acid) by varying aromatic polycarboxylate coligands. Structural analyses reveal that polymers 1–6 display diverse 3D frameworks and topologies, in which all of the N-donor ligands bmb exhibit trans-conformation but with different Ndonor···N–Csp3···Csp3 torsion angles. Polymer 1 shows a 3-fold interpenetrating dia array with a 4-connected 66 topology. Polymer 2 features a (3,4)-connected pillar-layered structure with (63)(65·8)-ins topology. Polymer 3 is a 4-connected framework with 66-dia topology and two types of meso-helical chains. Polymer 4 possesses a 2-fold interpenetrating 6-connected framework with (412·63)-pcu topology. The structure of polymer 5 is a 4-connected 5-fold interpenetrating architecture with 66-dia topology. Interestingly, in 6, part of bta3- anions are converted into a new ligand mta2- via in situ esterification reaction under solvothermal conditions. As a result, polymer 6 exhibits a scarce mixed-ligands framework with two O-donor and one N-donor ligands based on tetranuclear Cd(II) clusters. It is an 8-connected (36·418·53·6)-hex topology. A systematically structural comparison of these polymers indicates that the coordination modes of aromatic polycarboxylates along with the structural characteristics of the semirigid N-donor ligand bmb simultaneously play an important role in constructing the high-dimensional frameworks. Moreover, polymers 1–6 indicate high thermal stabilities and different photoluminescence behaviors in the solid state.