Nitrosyl complexes decomposition

Reductive nitrosylation, transition metal nitrosyl complexes, 34 296-297 ReFejSj cluster, 38 41-43 self-assembly system, 38 41-42 Refining, of actinide metals, see Actinide, metals, purification Refractory compounds heat treatment of solids, 17 105-110 crystal growth, 17 105, 106 decomposition, 17 107,-110 spheroidization, 17 106, 107 preparation of, using radio-frequency plasma, 17 99-102... 

The addition reactions of thiolates to NP are generally followed by the decomposition of the red adducts. A survey on the persistence of the red colors showed that the adduct with thiosuccinic acid was extremely stable over days (118). Some rationalization on the different adduct stabilities has been advanced thus, the presence of electron-rich or electron-withdrawing groups on the thiolate anion destabilize or stabilize the adducts, respectively. The great stability of the thiosuccinic acid adduct with NP has shown to be valuable for the quantitative determination of the nitrosyl complex (34,35). 

The decomposition of nitrosyl complexes has frequently been observed in acid solution, giving nitrous oxide, nitrogen or even ammonia. Here protonation must occur at the oxygen atom which is then removed as water. Further reaction gives gaseous products. An example9 is shown in equation (26). 

We have previously mentioned in Section 4.2 the chemistry developed by Selhnann etal, by using tetradentate or pentadentate S4 ligands. The use of such a ligand in nitrosyl ruthenium chemistry allowed the first conversion of a nitrosyl complex into a ruthenium HNO complex (31) by addition of NaBILi to [Ru(NO)(py S4)]Br. The formation and decomposition of HNO complexes is often invoked in many processes such as combustion of ftiels, oxidation of N2, reduction of HNO2, and so on. ... 

Unfortunately, the surface immobilization procedure was successful in avoiding one decomposition pathway, but it also uncovered the existence of a second. Nonetheless, it was possible to show that the catalytic abilities of the Ru-nitro group on the surface are unimpaired. Addition of acid to -(py)Ru(bpy)2N02+ in dry acetonitrile gives the nitrosyl complex which can be reconverted into the nitro form by the addition of a base and trace water (eq. 6). Oxidation of Ru -N02 to Ru -N02 in the presence of... 

On the other hand, (case ii) if the reaction of the donor with the metalloporphyrin is faster than its spontaneous decomposition rate, the metalloporphyrin reacts directly with the donor, accelerating its decomposition rate and forming the corresponding nitrosyl complex by azanone transfer to the metal center. For these cases, almost no free HNO is produced, as evidenced by the quantitative formation of the nitrosyl product even for equimolar metalloporphyrin to donor ratios. In these cases, the Uobs against [Donor] plot gives a straight line from which the bimolecular cat(Donor) rate constant can be obtained. 

At the time we reported the pK for [Fe(CN)5HNO], we had payed no much attention to our own previous computational DFT result predicting that [Fe(CN)5NO] was an unstable species that should lose CN from the coordination sphere, in contrast with the successfial predictions on the stabihty of other 5C and 6C cyano-nitrosyl complexes (12). Anyway, we considered a plausible decomposition route for the putative [Fe(CN)5NO]" intermediate, involving the frans-labdization of cyanide (Equation 30) ... 

Catalase (EC 1.11.1.6) rapidly formed a reversible complex stoichiometrically with nitric oxide with the Soret band shifting from 406 to 426 nm and two new peaks appeared at 540 and at 575 nm, consistent with the formation of a ferrous-nitrosyl complex (Brunelli et al. 2001). Catalase consumed more nitric oxide upon the addition of hydrogen peroxide. Conversely, micromolar concentrations of nitric oxide slowed the catalase-mediated decomposition of hydrogen peroxide. Catalase pre-treated with nitric oxide and hydrogen peroxide regained full activity after dialysis. 

No Raman measurements have as yet been reported on nitrosyl complexes, due to their colors and ease of decomposition, but the advent of laser sources will no doubt stimulate research in this area. 

There are attempts to use other iron nitrosyls, both monomeric complexes and clusters [85-90]. Photochemical liberation of NO follows three main reaction pathways (1) photooxidation-substitution, (2) photoreduction, and (3) ligand rearrangement or decomposition as a result of photoreaction. 

In order to know whether the Pd ions or complexes are anchored to the zeolite framework or not, the IR framework vibrations of Pd-H-ZSM-5(0.49) were investigated (Figure 5). After activation under O2, a weak band at 930 cm" forms. Upon NO adsorption, the 930 cm band disappear while a new band appears at 980 cm". These bands are attributed to asymmetric internal stretching vibrations of T-O-T bonds (T = Si or Al) perturbed by Pd ions. The higher the perturbation, the lower the frequency. Therefore, the 930 cm band could be related to anchored Pd(II) ions or complexes formed upon decomposition of exchanged complexes, and the 980 cm band could be due to Pd(I) nitrosyl entities formed upon NO contact. Similar observations were found on Cu-ZSM-5 catalysts (34). 

The complexes reported above are green, crystalline solids (mp 1,218-220° dec. 2, 190-195° dec.) that are moderately stable in air (decomposition over a period of several months is noted). The complexes are very soluble in acetonitrile and just moderately soluble in nitromethane and dichloromethane. Their solutions are not very stable in air. They are insoluble in alcohols, benzene, diethyl ether, and hexane. The complexes exhibit a nitrosyl stretching frequency at 1541 cm"1... 

Figure 2 includes an additional, parallel route for the decomposition of Ii, as revealed by the distinctive EPR signature of the final product at pH 5. We proposed it to be also a dinitrosyl species, [Fe(CN)2(NO)2] (I2). new member of the well-characterized series of paramagnetic distorted tetrahedral complexes with different L ligands, described as Fe(NO)2 - These species behave as reversible, labile NO carriers, involved in trans-nitrosylation processes. EPR signals ass nable to these dinitrosyl complexes have been found in tissue of ascite tumors of mice upon injection with SNP. Those containing L = thiolates and imidazole were found to activate sGC promoting vasodilation (140). 

---