Osmiamates

Osmiamates, e.g. K.OSO3N (K20s04(0H)2 plus ammonia) are stable and related species, e.g. [Os NC ], can be formed by substitution. 

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

The osmiamate ion, Os03N, is isoelectronic with Os04. The yellow potassium salt is the most convenient one to prepare other, less soluble, salts, can be made by metathesis ... 

Reaction with ammonia in aqueous potassium hydroxide yields orange red crystalline osmiamate , K[N=0s03]. 

C. TRIOXO (f-BUTYLNITRIDO) OSMIUM (VIII)8 (W-f-Butyl Osmiamate)... 

Potassium nitridorhenate, 6 167 Potassium nitridotrisulfate, 2 182 Potassium nitrocarbamate, potassium salt, 1 68, 70 Potassium V-nitrosohydroxylamine-V-sulfonate, 5 117 by metathesis, 6 120 Potassium octacyanomolybdate(IV) 2-hydrate, 3 160 Potassium osmiamate, 6 204... 

Potassium osmiamate, K[Os( VIII )03N], is prepared by the addition of aqueous ammonia to a solution of osmium tetroxide, 0s04, in caustic potash solution (6). X-ray studies show the molecule to be basically... 

Potassium osmiamate forms pale yellow crystals. 

Os(VI) complexes of type [Os(VI)NX5]2- or [0s(VI)NX4H20]-(X = Cl, Br, CN, ox) are made by the action of the appropriate acid HX on potassium osmiamate (6, 11). The tendency to lose the ligand trans to the nitride and to substitute a water molecule is some evidence of a trans labilizing effect of jr-donor ligands. X-ray studies show a distorted octahedral structure with the osmium atom slightly out of the plane of the equatorial X atoms towards the nitride (1). The Os=N stretching frequency is around 1080 cm-1 (11) in such complexes. 

Osmiamic Acid, OsNOsH, may be prepared by decomposing the barium salt with dilute sulphuric acid, or the silver salt with hydrochloric acid. The dilute aqueous solution thus obtained is fairly stable, but upon concentration it decomposes. 

Joly 8 suggested that osmiamic acid might well be represented as a nitroso compound by the formula OsO(NO)OII, derived from the unknown trihydroxv compound, Os(NO)(OH)s, which corresponds to Ru(NO)(OH)3. 

Potassium Osmiamate, OsN03K, may be obtained 3 by the action of ammonia on a cold solution of osmium tetroxide in potassium hydroxide. Thus ... 

In various cases not all coordinated ions are the same, but the same sized fluorine and oxygen ions occur side by side, as in the series of isomorphous compounds K3ZrF7, K3TaOF6, K3wo2F5, also nitrogen with oxygen in the osmiamates ... 

There are now a substantial number of nitrido complexes of osmium(VI) and osmium(IV) as well as the osmiamate ion [OsVII 03N]. In addition to the ammine and ethylenediamine complexes, much recent work has been carried out on the bipy, phen and terpy complexes, often in connection with research into the photodissociation of water. The nitrosyl chemistry of the element, though seemingly not as extensive as that of ruthenium, has received much attention, and there has been considerable work on the phosphine, arsine and stibine complexes. 

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