CHAINS OF CENTERED METAL-CLUSTERS WITH A NOVEL RANGE OF DISTORTIONS - PR3I3RU, Y3I3RU, AND Y3I3IR

The phases R3I3Ru (R = La, Pr, Gd, Y, Er) and R3I3Ir (R = Gd, Y) are obtained from the reactions of R, RI3, and Ru or Ir for 3-4 weeks in sealed Ta tubing at 850-975-degrees-C, depending on the system. The title phases have been characterized by single-crystal X-ray means at room temperature, with space group P2(1)/m and Z = 2 (Pr3I3Ru, Y3I3Ru, Y3I3Ir, respectively: a = 9.194 (1), 8.7001 (4), 8.6929 (7) angstrom; b = 4.2814 (5), 4.1845 (2), 4.2388 (4) angstrom; c = 12.282 (2), 12.1326 (6), 12.092 (2) angstrom; beta = 93.46 (1), 94.769 (5), 94.73 (1)-degrees; R/R(W) = 3.7/3.4, 3.2/5.5, 4.4/4.0%). The first phase contains quasi-infinite double chains of edge-sharing Pr6(Ru) octahedra that are sheathed and interbridged by iodine. An evidently continuous distortion of these chains parallels the a/b axial ratio (in the order listed in the first sentence) such that metal octahedra are no longer obvious in Y3I3Ir; rather chains of trans-edge-sharing square pyramidal Y4Ir units bonded base-to-base are more apt. Increased R-R, R-interstitial, and interstitial-interstitial bonding appears to parallel the degree of distortion. Magnetic data for La3I3Ru and Pr3I3Ru and the results of extended Huckel band calculations on Pr3I3Ru are reported. Polar covalent Pr-Ru interactions and at least a quasi-closed shell configuration are emphasized by the latter.