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

Abstract

The solvothermal reactions of cobalt­(II) chloride hexahydrate and 1,3,5-benzenetribenzoic acid (H₃BTB) in anhydrous <i>N</i>,<i>N</i>′-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 <i>C</i>₃ 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], <b>1</b>, 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 <b>kgd</b> 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 <b>2</b>, with an unprecedented 3,6-connected net topology with the point symbol (4³)₂(4³·12¹²). The 2-D layered framework, <b>1</b>, shows a significant sorption hysteresis for adsorbates with relatively strong interactions with the framework, such as N₂ and CO₂