Darstellung und Kristallstruktur von [(NH3)5Rh(H7O4)Rh(NH3)5](S2O6)2,5 · H2O (1). Ein gemischtes Aquopentamminrhodium(III)-hydroxopentamminrhodium(III)- dithionat mit einer neuartigen μ-H7O4-Struktureinheit / Preparation and Crystal Structure of [(NH3)5Rh(H7O4)Rh(NH3)5](S2O6)2,5 · H2O (1). A Mixed Aquopentaamminerhodium(III)-hydroxopentaamminerhodium(III) Dithionate with a Novel μ-H7O4 Structural Unit
The title compound 1 can be obtained from an aqueous solution of aquopentaammine rhodium(III) dithionate and hydroxopentaammine rhodium(III) dithionate. The crystal structure has been determined from single crystal X-ray diffraction data and refined to R = 0.035 for 4390 unique reflections. Crystal data: monoclinic, space group P21/c, a = 1300.9(5) pm. b = 1472.3(6) pm. c = 1478.8(9) pm, β = 106.20(4)°, Z = 4.In the crystal dinuclear rhodium cations with point group symmetry 1 (C1) are found. A central μ-H3O2-bridge is formed by strong hydrogen bonding between aquo and hydroxo ligands; this bridge is additionally coordinated by two molecules of water. The entire bridging system is therefore H7O4-(H3O2- · 2 H2O). O-O distances characterizing the strength of the three hydrogen bonds within this new kind of structural unit are O(H2O-Rh 1)-O(HO-Rh2): 248 pm. O(H2O-Rh 1)-O(H2Oa): 273 pm, O(HO-Rh2)-O(H2Ob): 287 pm. The hydrogen atoms involved in these bridges have been located. The small difference in the Rh 1-O(H2O) - (205.4(3) pm) and Rh2-O(OH)- (204.3(3) pm) distances indicates that the entire H7O4-- moiety serves as a μ-bridging unit between Rh 1 and Rh 2