Two pillared-layer metal–organic frameworks constructed with Co(ii), 1,2,4,5-benzenetetracarboxylate, and 4,4′-bipyridine: syntheses, crystal structures, and gas adsorption properties

Abstract

Two new metal–organic frameworks (MOFs) [Co₂(btec)(bipy)₂(DMF)]·DMF·3H₂O (1) (btec = 1,2,4,5-benzenetetracarboxylate; bipy = 4,4′-bipyridine; DMF = N,N′-dimethylformamide) and Co₂(btec)(bipy)(DMF)₂ (2) were synthesized with the same starting materials under different solvothermal conditions. The higher temperature favors the generation of compound 2, while the slightly lower temperature with the higher bipy ratio leads to the porous structure of compound 1. Their structures are determined by single-crystal X-ray diffractions. Compound 1 is a 3D pillared-layer framework with interconnected channels along two directions after the removal of free guest molecules. The BET (Brunauer–Emmett–Teller) surface area of 1 was calculated to be 596 m² g⁻¹ by nitrogen adsorption at 77 K. The hydrogen adsorption isotherm at 77 K shows an excess uptake of 1.1 wt% at 15 bar. The heat (Q_st) of hydrogen adsorption was estimated to be 7.3 kJ mol⁻¹ at zero coverage. In compound 2, the wave-like layers constructed with btec are further pillared by bipy, giving rise to the 3D framework with the 1D channels occupied by coordinated DMF molecules.