Iridium structure

Engstrom J R, Goodman D Wand Weinberg W H 1986 Hydrogenolysis of n-butane over the (111) and (110)-(1 2) surfaces of iridium a direct correlation between catalytic selectivity and surface structure J. Am. Chem. Soc. 108 4653... 

The metals are lustrous and silvery with, in the case of cobalt, a bluish tinge. Rhodium and iridium are both hard, cobalt less so but still appreciably harder than iron. Rhodium and Ir have fee structures, the first elements in the transition series to do so this is in keeping... 

For iridium the position is reversed. This time it is the black dioxide, Ir02, with the rutile structure (p. 961), which is the only definitely established oxide. It is obtained by heating the metal in oxygen or by dehydrating the precipitate produced when alkali is added to an aqueous solution of [IrCl6] . Contamination either by unreacted metal or by alkali is, however, difficult to avoid. The other oxide, Ir203, is said to be... 

All the trihalides are known to have 6-coordinate iridium (except the unknown structure of Irl3). IrF3 has the PdF3 structure a-IrCl3 and IrBr3 have structures of the A1C13 type (Ir—Cl 2.30-2.39 A in the former). 

Other binary compounds include MAs3 (M = Rh, Ir), which has the skutterudite (CoAs3) structure [33] containing As4 rectangular units and octahedrally coordinated M. The corresponding antimonides are similar. M2P (M = Rh, Ir) has the anti-fluorite structure while MP3 has the CoAs3 structure. In another compound of this stoichiometry, IrSi3, 9-coordination exists for iridium. 

The iridium(II) complexes are rarer that those of rhodium(II). Iridium does not seem to form carboxylates Ir2(02CR)4 with the lantern structure complexes analogous to trans-RhX2 (PR3 )2 are not formed with bulky tertiary phosphines, probably because the greater strength of Ir-H bonds leads to IrHX2(PR3)2. 

No structural studies have been reported on these complexes, but detailed study of their vibrational spectra permits the assignments shown in Table 2.13. Like the rhodium analogues, iridium ammines are photoactive therefore, on excitation of ligand-field bands, solutions of [Ir(NH3)6]3+ or [Ir(NH3)5Cl]+ afford [Ir(NH3)5(H20)]3+. 

Figure 2.91 Structural data for iridium(III) complexes of dimethylphenylphosphine.

Table 2.14 Structural data for iridium nitrosyl complexes...

Comparison of four pairs of compounds where the structures of both rhodium and iridium analogues are known shows dangers of drawing correlations between spectra and structure, even with isoelectronic compounds. 

M(NO)(OCOCF3)2(PPh3)2. Both these complexes have 5-coordinate geometries with monodentate carboxylates. The rhodium compound has a square pyramidal structure with bent Rh-N-O (122°) but the iridium compound has a tbp structure with straight equatorial Ir-N—O (178°). The position of i/(N—O) reflects this difference (1800 cm-1 (Ir) and 1665 cm-1 (Rh)). 

The trimesityl of iridium can be made by reaction of IrCl3(tht)3 with MesMgBr, while IrMes4 can be oxidized to the cationic iridium(V) species [IrMes4]+, also tetrahedral (with concomitant slight Ir-C bond changes from 1.99-2.04 A in the neutral compound to 2.004-2.037 A in the cation). Another iridium(V) species, IrO(Mes)3 has been made [190], it has a tetrahedral structure (lr=0 1.725 A). 

Iridium Coating for Spacecraft Rocket Nozzles. The coating of rocket nozzles with iridium is a good example of the ability of CVD to provide a complete composite material, in this case a structural refractory shell substrate coated with a corrosion- and oxidation-resistant component. The device is a thruster rocket nozzle for a satellite. The rocket uses a liquid propellant which is a mixture of nitrogen tetroxide and monomethyl hydrazine. 

Iridium chemistry also holds a rare example of a monodentate guanidinate ligand. The monomeric parent amido complex Cp Ir(PMe3)(Ph)(NH2) cleanly undergoes an insertion reaction on treatment with diisopropylcarbodiimide (Scheme 153). Spectroscopic data and an X-ray structural analysis revealed the presence of a nonchelating guanidinate ligand. ... 

Hydride Complexes of Ruthenium, Rhodium, and Iridium G. L. Geoffroy and J. R. Lehman Structures and Physical Properties of Polynuclear Carboxylates Janet Catterick and Peter Thornton... 

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