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853831 
Journal Article 
Hydrolytic polymerization of rhodium(III). 1. Preparation, solution studies, and x-ray structure of the doubly bridged dimer [(H2O)4Rh(.mu.-OH)2Rh(OH2)4](dmtos)4.cntdot.8H2O 
Cervini, R; Fallon, GD; Spiccia, L 
1991 
Yes 
Inorganic Chemistry
ISSN: 0020-1669
EISSN: 1520-510X 
30 
4 
831-836 
WOS:A1991EY44300042 
Several polynuclear Rh(III) species, formed on addition of excess base to solutions of [Rh(OH2)6]3+, have been separated by ion-exchange chromatography. Solution characterization studies, viz. charge (4+) and charge/Rh (2.1 (+/- 0.1)), have confirmed that the doubly bridged hydrolytic dimer [(H2O)4Rh(mu-OH)2Rh(OH2)4]4+ is one of the species formed. The UV-vis spectrum of the dimer shows an intense peak at 242 nm (epsilon approximately 1750 M-1 cm-1), which is attributed to an OH--->Rh charge-transfer transition. Addition of dimer solutions to a pyridine buffer yields a fine yellow precipitate of the "active" dimer hydroxide of Rh(III), which consists of discrete dimer units and dissolves rapidly in acid to regenerate solutions of the hydrolytic dimer. Crystalline salts of the hydrolytic dimer of Rh(III) were obtained from concentrated dimer solutions prepared by dissolving the active hydroxide in either mesitylene-2-sulfonic acid or p-toluenesulfonic acid. Electron microprobe and elemental analyses of the mesitylate salt were consistent with the composition [(H2O)4Rh(mu-OH)2Rh(OH2)4]((H3C)3C6H2SO3)4.8H2O. The complex crystallizes in the monoclinic space group P21/c with cell parameters a = 17.981 (8) angstrom, b = 9.324 (3) angstrom, c = 17.367 (5) angstrom, beta = 96.40 (3)-degrees, and Z = 2. Least-squares refinement of the structure gave a final R value of 0.048 for 3151 observed reflections. The structure consists of double layers of the anions with the SO3- groups pointing toward the complex cation. An extensive H-bonding network links the coordinated ligands, waters of crystallization, and SO3- groups. The nonbonded Rh***Rh and O***O distances within the bridging moiety are 3.030 and 2.645 angstrom, respectively, while the O-Rh-O and Rh-O-Rh angles within the bridge are 82.20 and 97.40-degrees, respectively. The Rh-O bridging distances (1.999 (5) and 2.023 (5) angstrom) are somewhat shorter than the terminal Rh-O distances (2.028 (5)-2.068 (5) angstrom). The uncertainty in each distance makes it impossible to ascertain whether the OH- bridges exert a significant trans influence.