Coordination Polymers Driven by Urea-Diisophthalate Linkers: From Hydrothermal Assembly and Structural Diversity to Catalytic Applications

Eight new metal(II) coordination polymers (CPs) were assembled via hydrothermal methods from an unexplored urea-diisophthalate linker, 5,5'-(carbonylbis(azanediyl))diisophthalic acid (H4cada) and different N-donor auxiliary ligands (phen: 1,10-phenanthroline; bipy: 2,2'-bipyridine; H2biim: 2,2'-biimidazole; bpa: bis(4-pyridyl)amine; dpey: 1,2-di(4-pyridyl)ethylene; or dpea: 1,2-di(4-pyridyl)ethane). The obtained products were identified as [Mn(μ3-H2cada)(phen)(H2O)]n·2nH2O (1), [Mn2(μ4-cada)(phen)3(H2O)]n·2nH2O (2), [M2(μ5-cada)(bipy)2(H2O)2]n·3nH2O (M = Mn (3) and Cd (4)), [Cd2(μ5-cada)(H2biim)3]n·2nH2O (5), [H2bpa]n[Mn(μ3-cada)(H2O)2]n·3nH2O (6), [Co2(μ6-cada)(μ-dpey)0.5(H2O)4]n·2nH2O (7), and [Mn2(μ6-cada)(μ-dpea)0.5(H2O)4]n·2nH2O (8). These CPs were analyzed by standard methods, including powder and single-crystal X-ray diffraction, revealing structures ranging from 1D chains (2) and 2D layers (1 and 3-6) to 3D networks (7 and 8) with different topologies. All of the obtained CPs were also screened as heterogeneous catalysts for the C-C coupling reaction of pyridine-4-aldehyde (model substrate) with nitromethane. Substrate scope and the effects of reaction time, temperature, solvent type, catalyst loading, and recycling were explored, allowing us to identify highly efficient (up to 99% product yields), selective, and recyclable catalytic systems. This work widens the family of functional coordination polymers driven by urea-derived linkers and highlights the promising application of these materials in catalysis.