The Crystal and Molecular Structure of Iodomethylnitrosylbis(triphenylphosphine)iridium, IrI(CH₃)(NO)(P(C₆H₅)₃)₂

The structuee of iodomethylnitrosylbis(triphenylphosphine)iridiurrii IrI(CH₃)(NO)(P(C₆H₆)₃)₂, has been determined from three-dimensional X-ray data collected by counter methods. The compound crystallizes in the space group C_2h ⁶-I2/a of the monoclinic system with four molecules in a unit cell of dimensions a = 16.011 (11) Å, b = 9.817 (9) Å, c = 22.445 (16) Å, β = 105.2(2)°. The observed and calculated densities are 1.74 (±0.02) and 1.73 g/cm,³ respectively. Least-squares refinement of the structure has led to a final value of the conventional R factor (on F) of 0.033 for the 1304 independent reflections having F² > 3σ(F²). There is a crystallographic twofold axis imposed on the molecule. The immediate coordination around the iridium is approximately square pyramidal with the nitrogen atom of the nitrosyl group occupying the apical position and the other ligands lying hi the basal plane. The twofold axis leads to a disorder of the mutually trans iodo and methyl ligands and also to a disorder of the nitrosyl group. Despite this disorder an iridium-nitrogen-oxygen bond angle of 120 (2)° may be derived from the data. Therefore this complex provides another example of the nitrosyl ligand coordinated as NO^- to a transition metal. Important bond lengths in the molecule are as follows: Ir-N, 1.91 (2) Å; Ir-P, 2.348 (3) Å; Ir-I, 2.726 (2) Å; Ir-C, 2.05 (4) Å; N-O, 1.23 (2) Å. This compound provides the first example of a five-coordinate complex in which a methyl group is trans to another ligand. The iridium-iodine bond length is approximately 0.06 Å longer than that found in related complexes, which is indicative of the trans bond weakening effect of the methyl group.