Two New (3,6)-Connected Frameworks Based on an Unsymmetrical Tritopic Pyridyldicarboxylate Ligand and Co2 Dimer: Structures, Magnetic, and Sorption Properties

By reacting a tritopic ligand 5-(4-carboxyphenyl)­nicotinic acid (H2cpna) with Co­(NO3)2 under different conditions, two new three-dimensional (3D) frameworks, [Co2(cpna)2(H2O)3]·DMF·9­(H2O) (1) and [Co4(cpna)4(H2O)8] (2), have been obtained. They exhibit (3,6)-connected topological nets based on Co2 clusters and Y-shaped trinodal cpna2– linkers. 1 presents a chiral anh net with the right-handed helical channels, while 2 shows an achiral framework with a rtl topology. The whole structures of 1 and 2 are constructed from 2D achiral layers interconnected by triangular cpna2– nodes. Notably, these layers contain two heterochiral vertical and parallel 21 helical chains for 1 and 2, respectively, and those chains are constructed with 4-connected tetrahedral or square planar centers in their respective layers. The magnetic studies indicate that 1 and 2 show antiferromagnetic and weak ferromagnetic exchanges transmitted through μ2-Owater/μ1,3-carboxylate bridges and carboxylate single μ2-O bridges between Co2+ ions in the Co2 dimers, respectively. In addition, 1 displays microporous sorption for N2 and CO2.