CRYSTAL-STRUCTURE AND MOSSBAUER-SPECTROSCOPY STUDIES OF THE FERRIMAGNETIC COMPLEX BIMETALLIC SALT HEXAAMMINECHROMIUM(III) HEXACHLOROFERRATE(III), [CR(NH3)6][FECL6]

The crystal and molecular structures of the ferrimagnetic bimetallic complex salt hexaamminechromium(III) hexachloroferrate(III), [Cr(NH3)6][FeCl6], have been determined from single-crystal, three-dimensional x-ray diffraction counter data. The compound crystallizes as orange coloured crystals in the space group C2/c of the monoclinic system with Z = 4 and has cell dimensions a = 11.325(1) angstrom, b = 11.387(1) angstrom, c = 11.233(1) angstrom, and beta = 90.83(1) angstrom. The structure was refined by using segmented block diagonal least-squares techniques to discrepancy indices R and R(w) of 0.0233 and 0.0285, respectively. The metal ions occupy sites with symmetry 1BAR and are nearly octahedrally coordinated. In the [FeCl6]3- anion there are three independent Fe-Cl distances with a mean of 2.393 (2) angstrom, and the maximum angular deviation from octahedral geometry is 1.2-degrees. In the [Cr(NH3)6]3+ cation, the mean of the three independent Cr-N distances is 2.079 (7) angstrom, and the maximum angular deviation from octahedral geometry is 0.7-degrees. The structural data provide an explanation for the observed quadrupole splitting of 0.214 mm s-1 as seen in the Mossbauer spectrum at 292.6 K and reveal superexchange pathways via close amine proton-chloride anion contacts with lead to 3D-ferrimagnetic ordering near 2.8 K.