Two Six-Connected MOFs with Distinct Architecture: Synthesis, Structure, Adsorption, and Magnetic Properties†

By assembling Co-II ions and a combination of 5-(4-pyridyl)tetrazole (4-ptz) and formate ions, two distinct metal-organic frameworks, [Co-3(4-ptz) (5)(HCOO)(H2O)(2)] and [Co-3(4ptz)(4)(dmf)(2)(HCOO)(2)] (dmf=N,N'-dimethylformamide), were synthesized. They were both characterized by single-crystal Xray diffraction, IR spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. Structural analyses revealed that by slightly modulating the coordination environment of the trinuclear cobalt cluster, two complexes were formed featuring unusual six-connected nets reminiscent of a pyrazole-type linear trinuclear cobalt cluster as compared with the classic eight-connected bcu topology. In addition, [Co-3(4ptz)(5)(HCOO)(H2O)(2)] interacted strongly with CO2, with an adsorption enthalpy of 29.2 kJmol(-1), and in a selectivity study, the uptake ratios of CO2/N-2 (from a 15: 85 mixture) and CO2/CH4 (50: 50 mixture) were 77.6 and 37.7, respectively. Magnetic studies on both complexes revealed weak antiferromagnetic coupling between the Co-II ions.