Ammine complexes iridium

Coordination Compounds. A large number of iridium complexes with nitrogen ligands have been isolated, particularly where Ir is in the +3 oxidation state. Examples of ammine complexes include [Ir(NH3)6]3+ [24669-15-6], [IrCl(NH3)]2+ [295894)9-1], and trans-[Ir(03SCF3)2(en)2]+ [90065-94 4]. Compounds of IV-heterocyclic ligands include trans- [IrCl4(py)2] [24952-67-8], [Ir(bipy)3]3+ [16788-86-6], and an unusual C-metalated bipyridine complex, [Ir(bipy)2(C3,N-bipy)]2+ [87137-18-6]. Isolation of this latter complex produced some confusion regarding the chemical and physical properties of Pi(bipy)3]3+ (167). 

The iridium(III) complexes are broadly similar to the rhodium(III) ammines a selection of synthesis is shown in Figure 2.84. 

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+. 

Fig. 7.63 Mossbauer spectra of some hexacoordinated ammine and pyridine complexes of trivalent iridium taken at 4.2 K with a source of Os in Os metal. The stick spectra indicate the positions and relative intensities of the individual resonance lines (from [285])...

All three elements form complex ammino-derivatives. Those of osmium have been very little investigated those of iridium are analogous to the anunino-derivatives of platinum on the one hand and to the ammincs of cobalt and chromium on the other whilst the platinum derivatives resemble those of cobalt, save that the metal in the platinic derivatives is tetravalent and not trivalent as in the cobalt-ammines. 

Ammonia unites readily with iridium salts, giving rise to complex ammino-derivatives. The first compounds described appear to be ammines analogous to those of palladium and platinum, to which they were compared by Berzelius 8 and Skoblikoff.4 A further series were described by Claus 5 wliich he represented like those of ammino-rhodium salts, as they bore a marked resemblance to these. After Jorgensen had established the constitution of the ammines of rhodium, cobalt, and chromium salts, Palmaer gave similar constitution to the iridium compounds. 

The procedure described here is based on the observation that amine monohydroxo complexes of cobalt(III), rhodium(IIl), and iridium(III) react directly with carbon dioxide to form the corresponding carbonato complexes,2 3 without effect on the configuration of the amine ligands.4 The amine monoaqua complex is allowed to react with lithium carbonate or carbon dioxide gas at room temperature at pH 8.0 for a few minutes, and the carbonato complex is isolated by adding alcohol. The procedure has been used to prepare salts of the following cations pentaammine(carbonato)-cobalt(III),2 ds-ammine(carbonato)bis(ethylenediamine)cobalt(III),5 trans-... 

Osmium(IV) ammines have unusually low pXa values (see Table 5) and so persist only in strongly acidic media the complexes are more acid by an order of five to six than their platinum(IV) counterparts but only slightly more acidic than the corresponding iridium(IV) complexes. This has been correlated with the decreasing t2g electron occupancy in the series PtIV-Irlv-OsIV and attributed to charge transfer from ligands to the empty n orbitals on osmium(IV). The cis isomers are more acidic than the trans, and this can be correlated with differences between the osmium(III) and osmium(IV) complexes for the isomers.55... 

The coordination chemistry of iridium is concerned primarily with the I, III and IV oxidation states complexes with iridium in the — 1,0, V and VI oxidation states are also known. Of these latter states, Ir-1 and Ir° are found in carbonylate anions, oligonuclear and substituted carbonyls, hydrides and ammines. Iridium(V) and (VI) complexes are predominantly hexahalide compounds. 

Iridium(O) is present in carbonyl and substituted carbonyl complexes, and perhaps in [Ir(NH3)5], if indeed this species exists. Although the ammine complex [Ir(NH3)5] has been reported,17 the diamagnetism of this complex suggests an irridium(I) hydride species. 

Ammonia forms complex derivatives with all three classes of iridium compounds. When added to iridious chloride, IrCl2, or to iridic chloride, IrCl4, the complex salts formed are analogous to the series of platinous and platinic ammine derivatives. When ammonia is added to the trichloride, many complex derivatives are formed which are similar to rhodic, cobaltic, and chromic compounds. For example, when ammonia acts upon ammonium iridiochloride a compound is produced having the formula [Cl(NHj)5lr]Cl2, and called chloro-pentammine-iridium dichloride. 

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