Nitrito- complexes

A typical value for the N O distance in nitro complexes is 124 pm whereas in nitrito complexes the terminal N-O (121pm) is shorter than the internal N-O(M) 129 pm. In the bidentate chelating mode (iii) the 2 M O distances may be fairly similar as in [Cu(bipy)2(02N)]N03 or quite different as in [Cu(bipy)(02N)2] ... 

One example was reported by Tolman and coworkers (78) who found that the copper(I) complex C Tp112 (TpR2=tris(3-(R2)-5-methylpyrazol-l-yl)hydroborate) promotes NO disproportionation via a weakly bound CuITpR2(NO) intermediate (formally a MNO 11 species). The products are N20 and a copper(II) nitrito complex (Eq. (36)). The rate law established the reaction to be first-order in copper complex concentration and second-order in [NO], and this was interpreted in terms of establishment of a pre-equilibrium between NO and the Cu(I) precursor and the Cux(NO) adduct, followed by rate-limiting electrophilic attack of a second NO molecule (mechanism B of Scheme 5) (78b). 

A detailed mechanistic study of the interactions of NO and N02 with MbFeIV = 0 (an analog of compound II above) was recently conducted by Herold and Rehmann (141). These authors demonstrated that MbFeIV= 0 reacts rapidly with NO to form an intermediate possessing a characteristics spectrum, consistent with the formation of the ferric nitrito complex MbFem(ONO). This reaction has analogy with the reactions of NO with the CrIV = O complex described above (112). 

Such a rearrangement, although seemingly unlikely, does occur with the nitrito complex as demonstrated by 0-nmr experiments ... 

Boldyreva EV (2001) Structural aspects of intramolecular solid-state linkage isomerization in Co(III) pentaammine nitro/nitrito complexes. Russ J Coord Chem 27 1-28... 

The formation of nitrito complexes provides a similar example, involving addition at the coordinated oxygen atom (Equation 35) (5). 

In the above instance the kinetically favored nitrito complex isomenzes to the thermodynamically favored nitro complex in seconds. 

The synthesis and chemistry of platinum nitrates has been recently reviewed.1621 The only homoleptic nitrate complex is K2Pt(N03)6 formed from K tBre and N2Os. Oxidation of the nitrito complex K2Pt(N02)4 gives K2Pt(N02)6> and not the nitrate complex. 

The reaction of [Pt(NH3)5(H20)]Cl4 with NaN02 in hydrochloric acid at 0°C yields the O-bonded nitrito complex [Pt(NH3)5(ONO)]Cl3, which isomerizes to the thermodynamically more stable N-bonded isomer (equation 479).1630... 

It is possible that in the use of alkali metal nitrites for nitrosyl synthesis, the first formed nitrito complex undergoes rapid ligand reduction similar to that above, as in equations (15) and (16). 

In plant solutions, up to 70% of the Ru(NO) 3+ may be in the form of inextractable nitrito complexes.305 However, as the nitrato species extract the mass action affect of the nitrate present may lead to the substitution of nitrite with nitrate, even though the former gives the more... 

Despite the considerable body of knowledge now available on the extraction chemistry of ruthenium, it remains a problematic element for fuel reprocessors. A variety of means10 may be used to render the ruthenium less extractable. These include the addition of reagents such as oxalate or thiourea, the oxidation of Ru111 to inextractable RuIV or the addition of nitrogen dioxide to retain more Ru(NO) 3+ in the form of nitrito complexes of low DRu. However, such treatments may have undesirable effects on plant operation. It is possible to attain high decontamination factors for ruthenium over several process cycles, the penalty being that the ruthenium will appear in several waste streams, not just the HAW from the first decontamination cycle. 

T FIGURE 20.17 Samples and structures of (a) the nitro complex [Co(NH3)5(N02)]2+, which contains an N-bonded N02- ligand, and (b) the nitrito complex [Co(NH3)5(ONO)]2+, which contains an O-bonded N02-ligand. 

Fig. 7. Molecular structure of the cation in the bridged iron(II) nitro/nitrito complex [(l)2Fe2 r 1-lV r 1-0)-N02 ]Br2PF6 (37) intramolecular hydrogen bonds are shown as broken lines.

The complex may contain some (10-20%) [(en)2Co(NH2, N02)Co(en)2](N02)4 as an impurity unless contact with nitrate ions is avoided.17 To avoid nitrate contamination, chlorine gas can be used to oxidize the peroxo complex.17 The complex is difficult to purify by recrystallization. The p-amido-p-nitrito complex is extremely unreactive. 

It is noteworthy that the successful synthesis of nitrito-nitro linkage isomers for other metal ammines was designed only after the mechanism of formation of [Co(NH3)50NO]2+ and its rearrangement had been elucidated.4 It was found that the nitrito complex is readily formed without the cleavage of the Co—0 bond ... 

The kinetic product then slowly rearranges by an intramolecular process to the stable isomer [(NH3)5Co—N02]2+. On this basis it was reasoned that it should be possible to obtain other nitrito complexes by operating at an appropriate pH and under mild conditions. 

The syntheses presented here are examples of two types of "ligand isomers (1) Nitrito complexes, [Ni 2-[(methylamino)-methyl]pyridine 2(ONO)2], and [Ni 2-[(methylamino)methyl]-piperidine)2(ONO)2] (2) Chelating nitrite groups, [Co(2,4,6-trimethylpyridine iV-oxide NCh ], [Co(2,6-dimethylpyridine iV-oxide) 2 (NO 2)2], and [Co(4-methylquinoline iV-oxide)2(N02)2]. 

Preparation of Nitrito Complexes 1. [Ni(2-[(methyIamino)methyl] pyridine ONOh]... 

Methods of preparing nitrito complexes of Ir(III) are shown in Scheme 3. Structural characterization of (NH4)3[Ir(N02)6l shows that each N02 ligand coordinates through the nitrogen atom (Ir-N = 2.060 A). The coordination of thiocyanate ligands (NCS ) is discussed in Section 6.6 in [Ir(NCS)6], the ligand exhibits Linkage Isomerism and... 

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