A robust anionic pillared-layer framework with triphenylamine-based linkers: ion exchange and counterion-dependent sorption properties

A new anionic pillared-layer cobalt(II) metal–organic framework combining 4,4′,4′′-nitrilotribenzoic acid (H3ntb) as a linker and terephthalic acid (H2bdc) as a pillar-ligand with the formula {((CH3)2NH2)2[Co3(ntb)2(bdc)]}n (JUMP-1, JUMP = Jena University Magnetic Polymer) has been solvothermally synthesized and characterized. The crystal structure of JUMP-1 was determined to belong to the orthorhombic space group Cmca. It displays a three-dimensional (3D) framework for which the topological analysis revealed a 3,8-connected net with a tfz-d topology. The 3-connected organic node is linked to an 8-connected secondary building unit composed of a linear trinuclear cobalt(II) cluster with a mixed arrangement of coordination geometries (Td–Oh–Td) leading to two-dimensional layers which are further linked by terephthalic acid to give the pillared-layer arrangement. The magnetic properties are characterized by an antiferromagnetic coupling between a central octahedrally coordinated cobalt(II) ion and two outer tetrahedral cobalt(II) centers, whereas only a very weak inter-cluster coupling is observed. Moreover, a moderate zero-field splitting is detected for the tetrahedral cobalt(II) ions. The organic counterions could successfully be exchanged by lithium ions under retention of the anionic 3D network leading to JUMP-1(Li). For both compounds JUMP-1 and JUMP-1(Li), N2 and CO2 adsorption isotherms were measured. The pore distribution analyses revealed improved microporosity for the lithium exchanged MOF.