Crystal structure and mössbauer spectroscopy studies of the ferrimagnetic complex bimetallic salt hexaamminechromium (III) hexachloroferrate (III), [Cr(NH₃)₆][FeCl₆]

Summary

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 groupC2/c of the monoclinic system with Z=4 and has cell dimensionsa=11.325(1) Å,b=11.387(1) Å,c=11.233(1) Å, and β=90.83(1)Å. 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$\bar 1$ and are nearly octahedrally coordinated. In the [FeCl₆]³⁻ anion there are three independent Fe−Cl distances with a mean of 2.393(2) Å, and the maximum angular deviation from octahedral geometry is 1.2⁰. In the [Cr(NH₃)₆]³⁺ cation, the mean of the three independent Cr−N distances is 2.079 (7) Å, and the maximum angular deviation from octahedral geometry is 0.7⁰. The structural data provide an explanation for the observed quadrupole splitting of 0.214 mms⁻¹ as seen in the Mössbauer spectrum at 292.6 K and reveal superexchange pathwaysvia close amine proton-chloride anion contacts with lead to 3D-ferrimagnetic ordering near 2.8 K.