Amino acid based MOFs: synthesis, structure, single crystal to single crystal transformation, magnetic and related studies in a family of cobalt and nickel aminoisophthales

Abstract

Four new 5-aminoisophthalates of cobalt and nickel have been prepared employing hydro/solvothermal methods: [Co₂(C₈H₅NO₄)₂ (C₄H₄N₂)(H₂O)₂]·3H₂O (I), [Ni₂(C₈H₅NO₄)₂ (C₄H₄N₂)(H₂O)₂]·3H₂O (II), [Co₂(H₂O)(μ³-OH)₂ (C₈H₅NO₄)] (III), and [Ni₂(H₂O) (μ³-OH)₂(C₈H₅NO₄)] (IV). Compounds I and II are isostructural, having anion-deficient CdCl₂ related layers bridged by a pyrazine ligand, giving rise to a bilayer arrangement. Compounds III and IV have one-dimensional M-O(H)-M chains connected by the 5-aminoisophthalate units forming a three-dimensional structure. The coordinated as well as the lattice water molecules of I and II could be removed and inserted by simple heating-cooling cycles under the atmospheric conditions. The removal of the coordinated water molecule is accompanied by changes in the coordination environment around the M²⁺ (M = Co, Ni) and color of the samples (purple to blue, Co; green to dark yellow, Ni). This change has been examined by a variety of techniques that include in situ single crystal to single crystal transformation studies and in situ IR and UV-vis spectroscopic studies. Magnetic studies indicate antiferromagnetic behavior in I and II, a field-induced magnetism in III, and a canted antiferromagnetic behavior in IV.