Crystal structures and magnetic properties of the honeycomb-lattice antiferromagnet M2(pymca)3(ClO4), (M = Fe, Co, Ni)

We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M-2(pymca)(3)(ClO4 ), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 angstrom and c = 5.996 angstrom for 1, a = 9.608 angstrom and c = 5.996 angstrom for 2, and a = 9.477 angstrom and c = 5.958 angstrom for 3 at room temperature. In these compounds, each pymca ligand connects to two M2+ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets. (C) 2016 Elsevier Masson SAS. All rights reserved