3D metal-organic frameworks based on Co(II) and bithiophendicarboxylate: Synthesis, crystal structures, gas adsorption, and magnetic properties

Abstract

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2'-bithiophen- 5,5'-dicarboxylate (btdc2-) [Co3(btdc)3(bpy)2].4DMF, 1; [Co3(btdc)3(pz)(dmf)2].4DMF.1.5H2O, 2; [Co3(btdc)3(dmf)4].2DMF.2H2O, 3 (bpy = 2,2'-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformami de) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co3(RCOO)6}, connected either by btdc2- ligands (1, 3) or by both btdc2- and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N2, O2, CO, CO2, CH4 adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m2.g-1 and promising gas separation performance with selectivity factors up to 35.7 for CO2/N2, 45.4 for CO2/O2, 20.8 for CO2/CO, and 4.8 for CO2/CH4. The molar magnetic susceptibilities X p(T) were measured for 1 and 2 in the temperature range 1.77-330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are µeff (300 K) ~ 4.93 µB. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2.