Ferro/antiferromagnetic interactions transmitted by double bridged carboxylate groups in 2D mixed-ligand transition metal coordination polymers

Three 2D coordination polymers with mixed ligands [M(bpe)(bba)] _n (M = Mn for 1, Co for 2 and Ni for 3, bpe = 1,2-bis(4-pyridyl)ethane, H ₂bba = isophthalic acid) have been synthesized and characterized by single crystal X-ray diffraction, PXRD, TGA and magnetic susceptibility measurements. The central metal ions of each have a distorted octahedral geometry and are bridged by μ ₂-η ¹:η ¹ carboxylate groups to form binuclear units with metal-metal separations of 4.318 (1), 4.463 (2) and 4.551 (3), respectively. The binuclear units are linked by bba ^2- to form 1D ribbons, which are further assembled through bpe ligands into a 2D grid structure. TGA analysis reveals that 1, 2, and 3 exhibit high thermal stability. The magnetic properties of 1, 2 and 3 were studied in the temperature range of 2-300 K. Analysis of the magnetic data reveals antiferromagnetic interactions in 1 as well as interesting ferromagnetic interactions in 2 and 3 between the anti-syn double carboxylate groups bridging metal ions.