Novel Co-based metal–organic frameworks and their magnetic properties using asymmetrically binding 4-(4′-carboxyphenyl)-1,2,4-triazole

Abstract

Two novel Co-based metal–organic frameworks (MOFs) were synthesised and characterised using an asymmetrically binding ligand, 4-(4′-carboxyphenyl)-1,2,4 triazole (Hcpt). The isolated [Co₃^II(μ₃-O)(OH)(cpt)₃(H₂O)₂]_n·xH₂O·yDMF, Co-MOF1, exhibits a rhombohedral crystal structure (space group, P6₃/mc), with a trinuclear cobalt core that resembles the MIL88 series. This MOF shows paramagnetic behaviour down to 2 K with no saturation of magnetisation up to 7 T. This is presumably due to a geometrically frustrated triangular arrangement of Co spins. The two-dimensional complex, [Co^II(cpt)(N₃)]_n, Co-MOF2, crystallises in a monoclinic crystal system (space group, C2/m). The magnetic measurements reveal metamagnetic behaviour for this complex with a critical field in the range of 700–1000 Oe.