Fe(III), Mn(II), Co(II), and Ni(II) 3,4,5-trihydroxybenzoate (gallate) dihydrates; a new family of hybrid framework materials

We report the synthesis, crystal structures, magnetic properties, and thermal behavior of a family of isostructural transition metal gallate dihydrates containing infinite chains of trans-corner-sharing MO6 octahedra. The gallates crystallize in the enantiomorphic space groups P3121 and P3221, chirality being imparted by helical motifs in the structure. Ni(C7O5H4)⋅2H2O: a=8.824(2)Å, c=10.644(2)Å; Mn(C7O5H4)⋅2H2O: a=9.063(2)Å, c=10.947(2)Å; Co(C7O5H4)⋅2H2O: a=8.910(2)Å, c=10.887(2)Å. The Co(II) and Ni(II) gallates exhibit antiferromagnetic behavior, with TN=43 and 19 K, respectively, while Mn(II) gallate is paramagnetic down to 5 K. High-temperature X-ray powder diffraction indicates that crystallinity is lost near 200 °C in all of the compounds. Decarboxylation of the gallate moieties is believed to facilitate this thermal decomposition.