Pernille Harris, Henrik Birkedal, Sine Larsen and Hans U. Güdel
A New Study of the Acid Rhodo Complex Salt [(NH₃)₅CrOHCr(NH₃)₅]Cl₅·H₂O Shows That the Crystals are Orthorhombic
Acta Cryst. Sect. B 53, 795-802 (1997)                 

Abstract: Diffraction data recorded at low temperature with Mo Ka form two different crystals have been used in the refinement of the structure of the acid rhodo complex salt, m-hydroxo-bis-[pentaamminechromium(III)] chloride monohydrate [(NH₃)₅CrOHCr(NH₃)₅]Cl₅·H₂O. Several structural models in two different tetragonal space groups have been investigated before a satisfactory description of the structure was obtained. The compound crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 16.155(3), b = 16.154(3), c = 14.750(7) Å and Z = 8. The apparent tetragonal symmetry arises due to rotation twinning of the crystals. The diffraction pattern is further complicated by tetragonal pseudo-symmetry of the chromium sites, which means that reflections with l = 2n + 1 are systematically weak. The two independent dimeric cations are involved in slightly different hydrogen-bond patterns. This observation and the relative orientation of the dimers in the crystal is in accordance with spectral and magnetic measurements.