3D Metal-Organic Frameworks Based on Co(II) and Bithiophendicarboxylate: Synthesis, Crystal Structures, Gas Adsorption, and Magnetic Properties

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2 '-bithiophen-5,5 '-dicarboxylate (btdc(2-)) [Co-3(btdc)(3)(bpy)(2)]Greek ano teleia4DMF, 1; [Co-3(btdc)(3)(pz)(dmf)(2)]Greek ano teleia4DMFGreek ano teleia1.5H(2)O, 2; [Co-3(btdc)(3)(dmf)(4)].2DMF.2H(2)O, 3 (bpy = 2,2 '-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co-3(RCOO)(6)}, connected either by btdc(2-) ligands (1, 3) or by both btdc(2-) and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N-2, O-2, CO, CO2, CH4 adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m(2).g(-1) and promising gas separation performance with selectivity factors up to 35.7 for CO2/N-2, 45.4 for CO2/O-2, 20.8 for CO2/CO, and 4.8 for CO2/CH4. The molar magnetic susceptibilities chi(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 mu(eff) (300 K) approximate to 4.93 mu(B). 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.