STRUCTURAL AND MAGNETIC CHARACTERIZATION OF THE CHROMIUM(III) DIMERS DI-MU-HYDROXO-BIS[(4-HYDROXO-2,6-DICARBOXYLATOPYRIDINE)AQUACHROMIUM(III)]TETRAHYDRATE, [CR(CHEL)(OH2)OH]2.4H2O, AND DI-MU-HYDROXO-BIS[(4-CHLORO-2,6-DICARBOXYLATOPYRIDINE)AQUACHROMIUM(III)] DIHYDRATE, [CR(CL-DIPIC)(OH2)OH]2.2H2O

The structural and magnetic properties of the dimeric chromium(III) complexes di-μ-hydroxo-bis[(4-hydroxo-2, 6-dicarboxylatopyridine)aquachromiurn(III)] tetrahydrate, (CrC7H6NO7)2 4H2O, [Cr(chel)(OH2)OH]2-4H2O, and di-μhydroxo-bis[(4-chloro-2, 6-dicarboxylatopyridine)aquachromium(III)] dihydrate, (CrC7H5ClNO6)2-2H20, [Cr(Cl-dipic)(OH2)OH]2-2H2O, have been investigated. The chel complex crystallizes in space group PI of the triclinic system with one dimeric formula unit in a cell of dimensions [FORMULA OMMITED] The structure has been refined by full-matrix least-squares techniques to a final value of the conventional R factor (on F) of 0.080 based on 1511 observations. The Cl-dipic complex crystallizes in the space group Cl of the triclinic system with two dimeric formula units in a cell of dimensions [FORMULA OMMITED] The structure has been refined to a final R factor of 0.042 based on 1303 observations. Both complexes consist of discrete dimeric units. The coordination around the chromium centers is roughly octahedral, the ligating atoms being the nitrogen and two oxygen atoms of the tridentate chel or Cl-dipic ligand, a water molecule, and two bridging hydroxo groups. The Cr-Cr separations and Cr-O-Cr angles are [FORMULA OMMITED] in the chel and Cl-dipic complexes, respectively. The magnetic susceptibilities of powdered samples of the two complexes have been fitted to the Van Vleck model. The data for the chel complex give an excellent fit to this model with a singlet—triplet splitting of 4.27 (3) cm-1. The data for the Cl-dipic complex do not fit as well, apparently because of the presence of a large quantity of impurity in the bulk sample, but the data indicate a singlet—triplet splitting of 10.24 (6) cm-1. © 1979, American Chemical Society. All rights reserved.