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)]·4DMF, 1; [Co(3)(btdc)(3)(pz)(dmf)(2)]·4DMF·1.5H(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, CO(2), CH(4) 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 CO(2)/N(2), 45.4 for CO(2)/O(2), 20.8 for CO(2)/CO, and 4.8 for CO(2)/CH(4). The molar magnetic susceptibilities χ(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 μ(eff) (300 K) ≈ 4.93 μ(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.