3,6-Connected Metal–Organic Frameworks Based on Triscarboxylate as a 3-Connected Organic Node and a Linear Trinuclear Co₃(COO)₆ Secondary Building Unit as a 6-Connected Node

The solvothermal reactions of cobalt­(II) chloride hexahydrate and 1,3,5-benzenetribenzoic acid (H3BTB) in anhydrous N,N′-dimethylacetamide (DMA) at two different reaction temperatures and reactant concentrations led to two 3,6-connected metal–organic frameworks (MOFs) with different net topologies based on the ligand as a C3 symmetric 3-connected organic node and the linear trinuclear cobalt carboxylate cluster, Co3(COO)6, as a 6-connected secondary building unit (SBU). MOF [Co3(BTB)2(DMA)4], 1, with a linear trinuclear cobalt carboxylate cluster, Co3(COO)6, and with an inversion point symmetry with “compressed trigonal antiprismatic” 6-connectivity, is a two-dimensional (2-D) layered structure of a 3,6-connected kgd net topology. However, the same linear trinuclear cobalt carboxylate cluster, Co3(COO)6, with a 2-fold point symmetry with “compressed trigonal prismatic” 6-connectivity leads to the three-dimensional (3-D) network of 2, with an unprecedented 3,6-connected net topology with the point symbol (43)2(43·1212). The 2-D layered framework, 1, shows a significant sorption hysteresis for adsorbates with relatively strong interactions with the framework, such as N2 and CO2.