Abstract
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 RegClg and Re3Br9 cluster complexes which are already well character- ized. The Re-Re distances are 2.440 (twice) and 2.507 A. The Re3Ig groups are linked into zigzag chains by bridging halo- gen atoms in a manner similar to that in which Re3Clg 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 P2i/m, with unit cell dimensions a = 9.234, b — 11.309, c = 8.799 A, ß — 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 RegXg derivatives. A similar reduction in angle in RegBrn2- was reported earlier by Penfold. A reexamination of the Re3Br9 unit which shows no such reduction in (CgBbNHhRejBris sug- gests that coordinated water molecules may be present.
lation to “Rel2” is briefly discussed.