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 °C, depending on the system. The title phases have been characterized by single-crystal X-ray means at room temperature, with space group P2₁/m and Z = 2 (Pr₃I₃Ru, Y₃I₃Ru, Y₃I₃Ir, respectively: a = 9.194 (1), 8.7001 (4), 8.6929 (7) Å; b = 4.2814 (5), 4.1845 (2), 4.2388 (4) Å; c = 12.282 (2), 12.1326 (6), 12.092 (2) Å; Å/² = 93.46 (1), 94.769 (5), 94.73 (1)°; 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 Hiickel band calculations on Pr₃I₃Ru are reported. Polar covalent Pr-Ru interactions and at least a quasi-closed shell configuration are emphasized by the latter.