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)]·H 2 O} 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 ), [Cd 2 (bmb)(bta)(mta) 0.5 ] n ( 6 ), (H 2 phda = phenylenediacetic acid, H 2 oba =4,4′-oxybis(benzoic acid), H 2 bpdc = biphenyl-4,4′-dicarboxylic acid, H 3 bta =1,2,4-benzenetricarboxylic acid, and H 2 mta = 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 N donor ···N–C sp3 ···C sp3 torsion angles. Polymer 1 shows a 3-fold interpenetrating dia array with a 4-connected 6 6 topology. Polymer 2 features a (3,4)-connected pillar-layered structure with (6 3 )(6 5 ·8)- ins topology. Polymer 3 is a 4-connected framework with 6 6 - dia topology and two types of meso-helical chains. Polymer 4 possesses a 2-fold interpenetrating 6-connected framework with (4 12 ·6 3 )- pcu topology. The structure of polymer 5 is a 4-connected 5-fold interpenetrating architecture with 6 6 - dia topology. Interestingly, in 6, part of bta 3- anions are converted into a new ligand mta 2- 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 (3 6 ·4 18 ·5 3 ·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.