CRYSTAL AND MOLECULAR STRUCTURE OF TRIRHENIUM NONAIODIDE

Rhenium(III) iodide has been obtained as well-formed single crystals by a modification of published preparative procedures. From X-ray diffraction data obtained with a counter diffractometer, the structure has been solved and refined to a final value for the conventional, unweighted residual of 4.4% for the 623 significant reflections. The substance is composed of Re3I9 molecules essentially similar in structure to the Re3Cl9 and Re3Br9 cluster complexes which are already well characterized. The Re-Re distances are 2.440 (twice) and 2.507 Å. The Re3I9 groups are linked into zigzag chains by bridging halogen atoms in a manner similar to that in which Re3Cl9 molecules are linked into sheets. Variations in Re-I bond lengths correlate well with the structural functions of the various I atoms in the molecule and crystal. Trirhenium nonaiodide crystallizes in the monoclinic system, space group P21/m, with unit cell dimensions a = 9.234, b = 11.309, c = 8.799 A, β = 110.25°. The measured density was 6.37 g cm-3 (in fact, a lower limit because of iodine loss) while that calculated for two formula units (Re3I9) per cell is 6.55 g cm-3. An important feature of the structure is that the off-plane I-Re-I angle at the Re atom not involved in intermolecular bridging is much smaller (131°) than the corresponding angles (150-160°) at Re atoms which have a fifth coordinated atom in many other Re3X9 derivatives. A similar reduction in angle in Re3Br112- was reported earlier by Penfold. A reexamination of the Re3Br9 unit which shows no such reduction in (C9B7NH)2Re3Br15 suggests that coordinated water molecules may be present. The limited chemistry of Re3I9 including a possible structural relation to “ReI2” is briefly discussed. © 1968, American Chemical Society. All rights reserved.