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-comer-sharing MO6 octahedra. The gallates crystallize in the enantiomorphic space groups P3(1)21 and P3(2)21, chirality being imparted by helical motifs in the structure. Ni(C7O5H4)center dot 2H(2)O: a = 8.824(2) angstrom, c = 10.644(2) angstrom; Mn(C7O5H4)center dot 2H(2)O: a = 9.063(2) angstrom, c = 10.947(2) angstrom; Co(C7O5H4)-2H(2)O: a = 8.910(2) angstrom, c = 10.887(2) angstrom. The Co(II) and Ni(II) gallates exhibit antiferromagnetic behavior, with T-N = 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 degrees C in all of the compounds. Decarboxylation of the gallate moieties is believed to facilitate this thermal decomposition. (c) 2006 Elsevier SAS. All rights reserved.