Ionothermal synthesis of a new cobalt metal-organic framework based on tetranuclear cobalt clusters

A new metal-organic network (EMIM)[Co2(hip)2(μ3-OH)]·H2O (1), (H2hip = 5-hydroxyisophthalic acid and EMIM = 1-ethly-3-methylimidazolium), has been synthesized by the ionothermal reaction of cobalt nitrate, H2hip and [EMIM]Br ionic liquid. Single-crystal X-ray diffraction analysis reveals that 1 exhibits a two-dimensional (2D) bilayer constructed from tetranuclear [Co4(μ3-OH)2] building units and hip2− linkers. There are square cavities with the dimension of 10.161 × 10.868 Å. The [EMIM]+ cations are located in the cavities, which have the hydrogen bonding interactions with the bilayer. Further more, the strong hydrogen bonds between the carboxylate and hydroxyl oxygen atoms of hip2− ligands and lattice water molecules extend the 2D layer into a 3D supramolecular network. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility and magnetization measurements, and the results reveal that there exist antiferromagnetic interactions.