A NEW STUDY OF THE ACID RHODO COMPLEX SALT [(NH3)(5)CROHCR(NH3)(5)]CL-5-CENTER-DOT-H2O SHOWS THAT THE CRYSTALS ARE ORTHORHOMBIC

Diffraction data recorded at low temperature with Mo K-alpha from two different crystals have been used in the refinement of the structure o f the acid rhodo complex salt, mu-hydroxo-bis[pentaamminechromium(III) ] chloride monohydrate [(NH3)(5)CrOHCr(NH3)(5)]Cl-5.H2O. Several struc tural models in two different tetragonal space groups have been invest igated before a satisfactory description of the structure was obtained . The compound crystallizes in the orthorhombic space group P2(1)2(1)2 (1), with a=16.155(3), b=16.154(3), c=14.750(7) angstrom and Z=8. The apparent tetragonal symmetry arises due to rotation twinning of the cr ystals. The diffraction pattern is further complicated by tetragonal p seudo-symmetry of the chromium sites, which means that reflections wit h l=2n+1 are systematically weak. The two independent dimeric cations are involved in slightly different hydrogen-bond patterns. This observ ation and the relative orientation of the dimers in the crystal is in accordance with spectral and magnetic measurements.