THE STRUCTURES OF FLUORIDES. Iresult of decreasing stability of the octahedral structure with decreasing cation size, with a consequent tendency to form fivefold and, finally, tetrahedral coordination. In the alkali metal niobates (Megaw, 1968b) The Crystal and Molecular Structure of Di-~t-hydroxobisldi(1,10-phenanthroline)chromium(III)l Chloride Hexahydrate BY JACK T. VEAL,* WILLIAM E. HATFIELD AND DEREK J. HODGSONt
Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27514, U.S.A. (Received 17 May 1972; accepted 14 September 1972)The crystal and molecular structure of di-/t-hydroxobis[di(1,10-phenanthroline)chromium(IlI)] chloride hexahydrate, [Cr(phen)2OH]2Cla.6H20, has been determined from three-dimensional counter X-ray data. The material crystallizes in the triclinic space group PI with two dimeric formula units in a cell whose dimensions are a= 14.056 (7), b= 11.296 (6), c= 18.990 (9) A, ~=87.15 (3), fl= 107-63 (2), and ),=74.68 (3) °. The observed and calculated densities are 1.39 (4) and 1.342 g cm -3 respectively. The structure has been refined by full-matrix least-squares techniques to a conventional R value of 0.077 for 3392 independent intensities greater than three times their estimated standard deviations. The complex consists of pairs of chromium atoms which are linked by two hydroxo bridges, with two 1,10-phenanthroline groups coordinated to each metal; the coordination geometry around each chromium is roughly octahedral. The average Cr-N and Cr-O bond lengths are 2-052 (6) and 1.927 (6) .~, respectively, while the Cr-Cr separation is 3.008 (3) ,& and the average Cr-O-Cr angle is 102-7 (4) °. The geometry of this complex is compared with that of [Cr(gly)2OH]2 and with those of complexes of the type [CuLOH]~. +, and the magnetic properties of the complex are discussed in terms of the bridging geometry.
