Nitrato complex

N2O4 has been extensively studied as a nonaqueous solvent system and it is uniquely useful for preparing anhydrous metal nitrates and nitrato complexes (p. 468). Much of the chemistry can be rationalized in terms of a selfionization equilibrium similar to that observed for... 

The nitrate group, like the nitrite group, is a versatile ligand and numerous modes of coordination have been found in nitrato complexes. ° The uncoordinated N03 ion (isoelectronic with BF3, B03 , C03 , etc.) is planar with N-O near 122 pm this value... 

Figure 30.5 Nitrato complexes of Ce". (a) [CefNOa) ] " the Ce" is surroundecl by 12 oxygen atoms from 6 bidentate nitrate ions in the form of an icosahedron (in each case the third oxygen is omitted for clarity). Note that this implies an octahedral disposition of the 6 nitrogen atoms, (b) [Ce(N03)4(0PPh3)2].

The structures of the oxime complex Co(NO)(dmg)2 (84) and its diphenylglyoxime analog exhibit strongly bent Co—NO groups, which are easily oxidized to the corresponding nitro compound.353 A mechanistic study of NO transfer from Co(NO)(dmg)2 to hemoglobin established that the reaction involves NO association with the protein subsequent to dissociation of NO from the Co complex.354 This mechanism is also consistent with the observation of nitrato complexes in reactions... 

An analogous nitrato complex, Be40(N03)6, is known in the solid state (145). The presence of a central 4-coordinate oxide ion and bridging nitrato ions has been confirmed by X-ray methods (146). The structures of these solid-state (jl4-oxo complexes lend support to the fi.roxo structures suggested for phosphato and carbonato complexes in solution (see Section IV). 

Nitrato complexes, osmium, 37 287 Nitrene, 33 101 Nitric acid... 

This is the optical density plotted against the time for an experiment in which we took the nitratopentamminecobalt complex in the presence of 0.50M thiocyanate ion since the competition ratio for thiocyanate ion and for water had been determined by Haim and Taube. Knowing the optical densities of all the possible reactants and products, we could calculate what the optical density should be as a function of time according to the mechanism of Haim and Taube. This calculation depends upon a rate constant for the aquation of the nitrato complex which we took from the literature. But one should get a continuously increasing optical density because the thiocyanate complex has a higher optical density than anything else. 

The decay of LMOONO, generated either as in Eq. (36), or by substitution of peroxynitrite into a metal complex, is usually written as a homolytic process of Scheme 9. The LMO and N02 so generated can then either diffuse apart or recombine within the solvent cage to either regenerate the peroxynitrito complex or form the metal-nitrato intermediate, followed by release of free nitrate by hydrolysis. At the time we initiated the work described below, there were no clear examples of LMOONO species isomerizing to a metal nitrato complex, although such reactions have been considered as a possibility (180-182). 

All the observations on the L2(H20)Rh002+ /N0 reaction are summarized in Scheme 10. This work, and a paper from Koppenol s group (191), have provided first credible examples of nitrato complexes... 

A number of well-defined nitrato complexes have been established. As mentioned above, the... 

In Table 81 the fundamental IR absorption bands of some representative nitrato complexes and of ionic nitrate are reported. 

Platinum(II) nitrato complexes can be synthesized by metathesis, by addition of N204 to Pt02(PPh3)2, by nitrosylation of Pt02(PPh3)2 or by ligand transfer reactions (equations 467-471). 

Nitrato complexes, with monodentate nitrate, are very similar to the fluorosulfates. Thus Au(N03)3 and the better characterized salts of [Au(N03)4]- are known. For example reaction of gold with N205 gives [N02]+[Au(N03)4]-, and the structure of K[Au(N03)4] has been determined.513-515... 

Zinc and cadmium nitrato complexes of the 2,6-diacetylpyridine derivatives (37) have been prepared, and reveal a variety of nitrate bonding modes.351... 

The sulfato and nitrato triphenylphosphine complexes were also obtained by the reaction of sulfuric or nitric acid with [Pd(PPh3)4] in ethanol.132 Nitrato complexes can also be prepared by isolation of [Pd(N03)2(H20)2], obtained by dissolution of Pd metal in concentrated nitric acid,133,134 and subsequent reaction with ligands L (e.g. L2 = 2,2 -bipyridyl).135 A crystal structure determination has been carried out for the complex cis-[Pd(N03)2(DM50)2].136... 

Iridium complexes having oxygen ligands are not nearly as extensive as those having nitrogen. Examples include acetylacetonates [Ir(P(C(5H5)3)2 (acac)H2] [64625-61-2], aqua complexes Ir(OH2)6]3+ [61003-29-0], nitrato complexes [Ir(0N02)(NH3),J2 [42482 42-8], and peroxides IrCl(P(C6I fy)3)2(02-/-(>/ I I9)2(CO) [81624-11-5]. Unlike rhodium, very few Ir(II) carboxylate-bridged dimers have been claimed and [Ir,2(OOCCI I3)4 has not been reported. Some Ir(T) complexes exhibit reversible oxidative addition of 02 to form Ir(III) complexes. That chemistry has been reviewed (172). 

Reaction with N03 yields an aqua nitrato complex (structure IX), and Kx =0.022 M 2 (25°C, 2 M NaN03) has been determined spec-trophotometrically. At very high nitric acid concentration, evidence for another nitrato complex has been obtained and a /i-amido-/i-nitrato complex is considered more likely than, e.g., a dinitrato complex (385). 

Nitro and nitrato complexes have been isolated from reactions of coordinated NO groups with oxygen. Thus, the formation of [Os(N02)CO(CNR)2(PPh3)2]+ (R = p-tolyl) has been reported36 (equation 31) and others 06 have oxidized Co(dmgH)2NO in aqueous acetone giving Co(dm-gH)2(N02)(H20). Similarly [Co(NO)(en)2]2+ in acetonitrile produces [Co(N02)(MeCN)(en)2]2+, and [Ru(NO3)O2(N0)2]20 in aqueous solution gives [Ru(N02)(N03)202(H20)] . 

There is a second possible reaction path. In the absence of an excess of compound (1) it is possible that compounds (3) could undergo an intramolecular rearrangement of the peroxy-nitrate group to the nitrato complex (6). 

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