Synthesis, Structure, and Magnetic and Catalytic Properties of Metal Frameworks with 2,2'-dinitro-4,4'-biphenyldicarboxylate and Imidazole-containing Tripodal Ligands

Based on 1,3,5-tris(1-imidazolyl)benzene (tib) and 2,2'-dinitro-4,4'-biphenyldicarboxylic acid (H2dnbpdc), four new metal-organic frameworks [M3(tib)(dnbpdc)3(H2O)2] [M = Mn (1), Cd (2)], [Zn3(tib)2(dnbpdc)2.5(Hdnbpdc)]·4DEF (3), and [Cd(tib)(dnbpdc)(H2O)]·DMF·H2O (4) (DEF = N,N-diethylformamide, DMF = N,N-dimethylformamide) were successfully synthesized. Isomeric 1 and 2 were unusual 8-connected uninodal three-dimensional (3D) frameworks with a point symbol of {3(3)·4(15)·5(9)·6}. Compound 3 was a (3,3,4,4)-connected 4-nodal 3D net with a point symbol of {4·6·8}2{4·6(2)}{4·8(5)}{6(2)·8(3)·10}, whereas 4 was a one-dimensional (1D) chain, which was further linked with neighboring 1D chains by hydrogen bonding interactions to give a 3D framework. It is interesting that 1 displayed ferromagnetic and antiferromagnetic interactions within the trinuclear Mn(ii) subunit. We also performed Knoevenagel condensation reactions catalyzed by activated 3 to demonstrate its heterogeneous catalytic property. Furthermore, the adsorption property of 3 was also investigated.