Five transition metal coordination polymers driven by a semirigid trifunctional nicotinic acid ligand: selective adsorption and magnetic properties

Abstract

Five coordination polymers, {[Co₃(L)₂(H₂O)₂]·4H₂O} (1), {[Cd₃(L)₂(NMP)₂]} (2), {[Cu(HL)]·NMP} (3), {[Cd(HL)(2,2′-bipy)]} (4) and {[Co(HL)(4,4′-bipy)(H₂O)₂]} (5) with different dimensional structures, have been solvothermally synthesized from a trifunctional N,O-building block, 5-(3,4-dicarboxylphenoxy)nicotinic acid (H₃L) that combines three distinct types of functional groups (COOH, N-pyridyl, and O-ether), and an auxiliary co-ligand, 2,2′-bipy or 4,4′-bipy (2,2′-bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine). H₃L contains three different types of functionalities and has eight potential coordination sites, which results in diverse coordination patterns and different dimensionalities depending on the reaction conditions. Complexes 1–3 display 2D layer structures with 1D channels, 4 shows a 2D + 2D → 2D interpenetrated wavy structure, while 5 exhibits a 1D chain structure. 1 demonstrates an effective storage capacity for CO₂ as well as high selectivity for CO₂ over CH₄ under ambient conditions. The magnetic properties revealed antiferromagnetic behaviors for complexes 1, 3 and 5. Also, the alternating-current susceptibility of 5 displays slow magnetic relaxation, showing interesting magnetic behavior with an effective energy barrier of 8.98 K.