Construction of Hybrid Bimetallic Uranyl Compounds Based on a Preassembled Terpyridine Metalloligand

Six hybrid uranyl–transition metal compounds [UO2Ni(cptpy)2(HCOO)2(DMF)(H2O)] (1), [UO2Ni(cptpy)2(BTPA)2] (2), [UO2Fe(cptpy)2(HCOO)2(DMF)(H2O)] (3), [UO2Fe(cptpy)2(BTPA)2] (4), [UO2Co(cptpy)2(HCOO)2(DMF)(H2O)] (5), and [UO2Co(cptpy)2(BTPA)2] (6), based on bifunctional ligand 4′‐(4‐carboxyphenyl)‐2,2′:6′,2′′‐terpyridine (Hcptpy) are reported (H2BTPA = 4,4′‐biphenyldicarboxylic acid). Single‐crystal XRD revealed that all six compounds feature similar metalloligands, which consist of two cptpy− anions and one transition metal cation. The metalloligand M(cptpy)2 can be considered to be an extended linear dicarboxylic ligand with length of 22.12 Å. Compounds 1, 3, and 5 are isomers, and all of them feature 1D chain structures. The adjacent 1D chains are connected together by hydrogen bonds and π–π interactions to form a 3D porous structure, which is filled with solvent molecules and can be exchanged with I2. Compounds 2, 4, and 6 are also isomers, and all of them feature 2D honeycomb (6,3) networks with hexagonal units of dimensions 41.91×26.89 Å, which are the largest among uranyl compounds with honeycomb networks. The large aperture allows two sets of equivalent networks to be entangled together to result in a 2D+2D→3D polycatenated framework. Remarkably, these uranyl compounds exhibit high catalytic activity for cycloaddition of carbon dioxide. Moreover, the geometric and electronic structures of compounds 1 and 2 are systematically discussed on the basis of DFT calculations. Uranyl CPs: Bimetallic uranyl coordination polymers (CPs) based on terpyridine metalloligands M(cptpy)2 (Hcptpy: 4′‐(4‐carboxyphenyl)‐2,2′:6′,2′′‐terpyridine; M: Ni2+, Fe2+, Co2+) were synthesized, and the application of these hybrid uranyl–organic framework materials in adsorption and catalysis of the cycloaddition of carbon dioxide with epoxides to form the corresponding cyclic carbonates were explored.