Osmium complexes crystal structures

Fig. 24. Comparison between the osmium- and ruthenium-arenes, exemplified by the respective [M(ri6-bip)Cl(en)]+ complexes. Although the crystal structures show the complexes to be isostructural with similar M-Cl bond lengths (a), the properties of the complexes are quite different, illustrated by the differences in hydrolysis rate h1/2), pAa, and 5 -GMP binding (the black box denotes the amount of OP03-bound 5 -GMP) (b).

The crystal structure of (ij4-cyclooctatetraene)(hexamethylbenzene)ruthenium (16) indicates bonding as a tetrahapto ligand60. For this complex and similar iron-, ruthenium- and osmium-(ij4-cyclooctatetraene)(arene) complexes, their XH and 13C NMR spectra exhibit only a single signal for the cyclooctatetraene ligand at temperatures as low as —145 °C. Using this temperature, the barrier-to-metal migration is estimated to be <6.6 kcal mol 1. 

There are a number of osmium(VI) oxo complexes containing cyanide ligand, but none have been reported for ruthenium. The ion [0s(0)2(CN)4] can be prepared by reaction of [OSO4] with aqueous KCN. The X-ray crystal structure of Cs2[Os(0)2(CN)4] (85) shows that it has trans-6ioxo groups with 0s=0 distances of 1.750 [0s(0)2(CN)4] is luminescent both in the solid state... 

A number of /.t-oxo-osmium(IV) porphyrin complexes have been prepared by aerial oxidation of [Os OEP)(CO)(MeOH)] in the presence 2,3-dimethylindole in CH2Cl2. " Cyclic voltammetric studies show that [0s2(0)(0EP)2(0Me)2] can undergo reduction to give an Os —O—Os dimer. The X-ray crystal structure of [0s(0EP)(0Me)]2( -0) shows a linear Os—O—Os backbone with Os—O and Os—OCH3 distances of 1.808 A and 1.997 A, respectively. 

Diol complexes, 9 211 d ion complexes, heavier, structure changes prior to ligand exchange, 34 258-259 Diopside, 4 61 crystal structure of, 4 51 p-Dioxane complexes, osmium, 37 312... 

In the solid state, the equilibrium is in favor of the hydrido complex (III), and its crystal structure and that of the osmium(II) analog have been determined (38). Chatt also observed that, on heating the equilibrium mixture of (II) and (III), naphthalene was eliminated and the product Ru(dmpe)2 was also a tautomeric mixture. Here the tautomer-ism involves breaking and re-formation of carbon-hydrogen bonds in the methyl groups of the phosphine ligands (IV and V) ... 

More recently a tetraimido osmium(VIII) compound has been formed by the reaction outlined in equation (90).236 The osmium complex subsequently formed in the further reaction with dimethyl-fumarate has been structurally characterized by a single crystal X-ray diffraction study (Figure 8).237 The structure conforms to the proposed general intermediate (8). 

The Criegee mechanism originally proposed involves the formation of an osmium(VI)-ester complex (106) from the [4+2] cycloaddition of the Osvul cis-dioxo moiety with an alkene, followed by the hydrolysis or reduction of (106) to cis-glycol and reduced osmium species. In support of this mechanism a variety of Osvl cyclic esters such as (107) or (108) (L = quinuclidine) have recently been synthesized from Os04 and the alkene, and characterized by an X-ray crystal structure.290,343 In solution the dimeric complex (108) dissociates to give the monomeric dioxo trigonal-bipyramidal complex (109), which is similar to (106).344... 

Many osmyl complexes with group VI ligands have been reported. The purple diamagnetic potassium osmate K2[0s(0H)4(0)2] is the best known and is a useful starting material for the preparation of other osmyl or osmium complexes. It is best prepared from the reaction of 0s04 with excess KOH. The X-ray crystal structure of K2[0s(0H)4(0)2] shows that the complex has the trans-dioxo unit, with a d(0s=0) of 1.77 A and a 0=0s=0 angle of 180° (238,239). The acid dissociation constants of H2[0s02(0H)4] have been determined. 

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