Nitrito and nitro mechanism. Their thermal properties and photoreactivities .
Nitrito and nitro mechanism In a CoIIIcomplex, nitro (N-bonded) coordination is thermodynamically more stable than the nitrito (O-bonded) form, but nitro-nitrito linkage isomerization may occur in the solid state by irradiation with visible or UV light (Balzani et al. This is in stark contrast with the opposite trend in nitro/nitrito alkanes, for which the nitro isomers are typically favored[7] (we predict by 7 kcal/mol for MeNO2). 11 More recently, a possible isomerization reaction pathway for square-planar complexes was discussed in two other articles. Photogeneration of Several Linkage Isomers and Investigation of Forward and Backward Nitro-Nitrito Isomerization Processes in a Palladium Complex Artem Mikhailov* The nitrite ion is an ambidentate ligand, which shows linkage isomerism. The reaction appears in no way different from the corresponding pentaamminecobalt(III) isomeri- zation. 4 It was found that the nitrito complex is readily formed without the cleavage of the Co—0 bond ACS Publications Nov 3, 2020 · Nitro–nitrito linkage isomerization is a well-known photochemical reaction of metal complexes in the solid state. To quantitatively elucidate the influence of the crystal environment on this reaction, we synthesized salts of a cationic platinum(II) nitrito complex with Pt(NO2)42– and (FSO2)2N– anions (1-Pt(NO2)4 and 1-FSA, respectively). Nitrite is processed by several enzymes, all of which utilize coordination complexes. light (350 nm) and the disc was removed for very brief periods from under the light to record the spectra. An alternative formula structure to emphasize the different coordinate covalent bond for the two isomers [C o (O N O) (N H 3) 5] C l: the nitrito isomer -O attached [C Some anionic nitrito complexes undergo acid-induced deoxygenation to give the nitrosyl complex. The reaction is fully retentive and the penta-ammine (nitro)cobalt () complex is the only species that could be detected by H n. A comparative study of the structures of nitrito- and nitropentaaminecobalt (III) dichloride Example 6 4 4 1: Nitro- vs. Nitro complexes also catalyze the oxidation of alkenes. Apr 2, 2024 · Abstract The linkage isomerization of NO2-ONO (nitro-nitrito) in the complex cation [Co(NH3)5NO2]2+ is a well-studied classical reaction. 9 For example, when one ammonia in hexaamminecobalt (III) is substituted by a nitrite anion, nitro, endo -nitrito, and exo -nitrito isomers are formed (Fig. Further studies of the differences in IR spectra between nitrito and nitro have been performed. For the nitrito isomer, the metal (Cobalt in this case) is connected to the oxygen of the ONO group, whereas for nitro isomer, the metal is connected to the nitrogen of the NO2 group. A crystallographic analysis claiming a solid state ferrous Mb further indicates an O‐ nitrito configuration (Copeland et al. The subsequent nitrito-ferrihaem complex (here depicted as O -nitrito, but the N- nitro is possible) exhibits some radical NO 2• -ferrohaem character, which can readily react with NO to generate diffusible N 2 O 3. Example 5 5 4 1: Nitro- vs. 3) RNH A 2 [O] RNO A 2 Nitration of alkanes is successful only when May 1, 2022 · The peak at 1640 cm −1 could be assigned to bridged nitrate or adsorbed NO 2 or NO 2− species (nitro), the peaks at 1573, 1509, and 1242 cm −1 are related to bidentate nitrate or NO 2− species (nitro, nitro-nitrito, monodentate), and the peak at 1372 cm −1 is free-like NO 3− or NO 2− species (nitro, nitro-nitrito, monodentate). An ambidentate ligand, nitrite has the potential to coordinate via the N- (nitro) or O- (nitrito) atoms in a manner that can direct its reactivity. 11More recently, a possible isomerization reaction pathway for square- planar complexes was discussed in two other articles. The normal coordinate treatment of the [Pt (NO2)4]2- ion has been carried out to give An ambidentate ligand, nitrite has the potential to coordinate via the N- (nitro) or O- (nitrito) atoms in a manner that can direct its reactivity. Oct 26, 2025 · Based on the kinetic parameters, the exo -nitrito isomer is slightly less stable for Ni-4d′. When donation is from nitrogen to a metal center, the complex is known as a nitro - complex and when donation is from one oxygen to a metal center, the complex is known as a nitrito - complex. Outer-Sphere electron-transfer and the effect of linkage isomerism in the titanium (III) reduction of nitro-pentacyanocobaltate (III) and nitro-, and nitrito-pentaamminecobalt (III) complexes in aqueous acidic media. . v. -1 region. 2 The following study seeks to identify the mechanism of conversion from [Co (NH3)5ONO]Cl2 to [Co (NH3)5NO2]Cl2, or from the nitrito derivative to the nitro derivative. It is believed that the photoisomerization of the nitro form to the nitrito form in the crystalline phase reaches complete transformation at a low temperature, while the reverse transformation proceeds as a first-order thermal intramolecular reaction upon Jan 1, 2018 · Theoretical investigation on the ground state properties of the hexaamminecobalt (iii) and nitro–nitrito linkage isomerism in pentaamminecobalt (iii) in vacuo † Photoisomerization reactions of some group 10 nitro complexes. [12] The mechanism of reaction will in both cases go through the o-bonded isomer (the nitrito-isomer), which is unstable and gradually converts to the N-bonded isomer (the nitro-isomer) in an equilibration process. Aug 17, 2023 · Electrochemical reduction of CuII → CuI indicates coordination isomerization from asymmetric nitrito-κ2-O,O to nitro-κ1-N. It must be noted that the $\ce {NO2}$ group can be coordinated to the metal atom in different ways such as nitro (via the nitrogen), nitrito (via oxygen), chelating via both oxygens (nitrito-O,O′), and bridging nitro, usually via nitrogen and oxygen atoms Oct 26, 2025 · However, quite recently, Warren et al. Nitrito complexes of nickel (II), copper (II) and cobalt (II) with tridentate pyrazole based planer ligand: Structure, spectroscopy, thermal properties and imitative nuclease activity. The nitrito–nitro isomerization in liquid ammonia runs faster than in an aqueous solution [31]. 6. after the reaction The figure below illustrates the bonding in nitrito (on the right) and nitro (on the left) Figure : Nitrito and Nitro linkage isomers. Distinguishing nitro vs nitrito coordination, along with the influence of the surrounding protein, is therefore of particular interest. , 2008). The electronic structure of the nitro and nitrito linkage isomers of cobalt (Ill) penta- ammines has been studied. 1). In the case of the photochemical nitro -+nitrito reaction, the KBr disc containing the nitro compound was irradiated with u. The nitrito–nitro linkage Isomerisation reaction of the penta-amminecobalt () complex in liquid ammonia proceeds entirely an intramolecular conjugate-base mechanism. However, quite recently Warren et al. Effect of the nature of other ligands on the rate of nitrito-to-nitro linkage isomerization of octahedral cobalt (III)-amine complexes in aqueous solution Katsuhiko Miyoshi , Noriko Katoda , and Hayami Yoneda The nitrito would undergo rapid decomposition (releasing HNO 2) to form a vinyl nitro product (Figure 1B-c), and iii) oxidation of the NO 2 -cLA radical intermediate to a nitro-peroxy followed by reduction of the peroxy to an alkoxy radical mediated by the oxidation of • NO to • NO 2. 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. Jun 18, 2001 · For the remaining nitrito complexes, the good IR spectra, together with the excellent retention of isosbestic points during the reaction, were taken as a full confirmation of the clean nitrito to nitro process observed [13]. 1 For instance, a Theoretical investigation on the ground state properties of the hexaamminecobalt (iii) and nitro–nitrito linkage isomerism in pentaamminecobalt (iii) in vacuo † Jan 1, 1989 · An infrared study of the nitro—nitrito linkage isomerization in solid nitro- and nitritopentamminecobalt (III) chloride An ambidentate ligand, nitrite has the potential to coordinate via the N- (nitro) or O- (nitrito) atoms in a manner that can direct its reactivity. Jan 30, 2004 · From these investigations, it is clear that N-bonded nitro isomer is more stable than O-bonded nitrio and conversion of nitrito to nitro could occur simultaneously both in solution and solid state via an intramolecular mechanism and the reaction rate is accelerated at elevated temperature [5], [6], [15]. , 2006), though disagreements still exist on the bonding mode as a computational study exploring NiR mechanisms favours N‐ nitro coordination in ferrous Hb (deoxyHb) (Perissinotti et al. Oct 26, 2025 · Both structures contain intermolecular hydrogen bonds to the ground state nitro- (η1-NO2) isomer, which are previously shown to limit the achievable level of nitro → nitrito photo-conversion. The nitrito isomer is less stable, and can be converted to the nitro isomer slowly by standing at room temperature, or quickly by heating or addition of HCl to a solution containing the nitrito compound. The preparations of these two linkage isomers are described. Transition-metal linkage isomers have the same chemical composition, differing only in the nature of the metal–ligand connectivity. The intramolecular rearrangement mechanism of nitro–nitrito isomerisation in metal complexes was initially conceptualized by Basolo and Hammaker. most common are unidentate bonding by an oxygen to give a nitrito complex and unidentate binding through the nitrogen to give a nitro complex. Their thermal properties and photoreactivities Aug 27, 2018 · Similarly, the nitrite anhydrase mechanism (path a) represents a situation where nitrite binds the methaem first. Jan 10, 2014 · The kinetic and thermodynamic of interconversion of nitro and nitrito isomers of pentaamminecobalt (III) complexes with various counterions were extensively studied in solution and in solid state mostly by UV–vis and IR spectroscopies, respectively. The factors There are several possible modes of coordination for this ligand of which the 'Author to whom correspondence should bc addressed. The kinetics and mechanism of the spontaneous nitrito-nitro isomerization in [Co (NH3)5ONO]CI2 [here we refer to the most recent paper by Phillips, Choi & Larrabee (1990)] and the photochemical nitro-nitrito isomerization in [Co- (NH3)sNO2]CI2 (Heyns & De Waal, 1989) have been studied by means of IR spectroscopy. The thermal nitrito– nitro isomerization in a polymer matrix (polyvinyl alcohol film) proceeds two times as fast as in an aque-ous solution [29], but it slows down by one order of magnitude when performed in the solid state [19, 30]. Nitrito- Linkage Isomers The cationic cobalt complex [Co (NH 3) 5 (NO 2)]Cl 2 exists in two separable linkage isomers of the complex ion: [Co (NH 3) 5 (NO 2)] 2+. Table 1. May 28, 2022 · Introduction The manifestation of two distinct isomers having the same chemical composition and molecular formula and differing only in the bond connectivity of the ligand to the metal is conventionally termed as linkage isomerism. m. 1) RH + HONO A 2 → RNO A 2 + H A 2 O by displacement reactions with nitrite ions, (24. The infrared spectra of nitro and nitrito complexes have been measured in the 5000 ∼ 400 cm. proposed a mechanism according to which the nitro isomer transforms to the exo-nitrito form first, and subsequently converts to the final photo-product, the endo- nitrito isomer. , 1968; Coppens et al. Isolation and spectroscopic characterization of 4 support this notion The mechanism of the isomerization in the solid state of nitritopentaamminecobalt(II1) dichloride to the thermodynamically more stable nitro compound and of the reverse photochemical nitro nitrito reaction have been investigated. According to Cio ni,33 experimental data do not provide a better understanding of the nitro/nitrito trans-formation mechanism, and theoretical methods can help in the elucidation of this reaction mechanism. 2. May 1, 2002 · Nitrito-nitro linkage isomerization in the solid state. Aliphatic nitro compounds also called as nitroparaffins are colourless liquids, used chiefly as industrial solvents An ambidentate ligand, nitrite has the potential to coordinate via the N- (nitro) or O- (nitrito) atoms in a manner that can direct its reactivity. Distinguishing nitro vs nitrito coordination, along with influence of the surrounding protein, is therefore of particular interest. We report here the preparation of the link- age isomers nitrito- and nitro-pentakis(methy1- amine)cobalt(III) dichlorides and some kinetic measurements for the nitrito to nitro isomeriza- tion in the solid and in aqueous solution. Special attention has been focused on the examination of the na- ture of the metal-ligand bonds in the two isomeric forms. Nitro compounds are considered to be derivatives of hydrocarbons in which one or more hydrogen atoms are substituted by nitro group. For example, the (NO 2-) ion is called nitro when it binds with the N atom and is called nitrito when it binds with the O atom. Dec 31, 1990 · Redox- and Thermally-Induced Nitro-Nitrito Linkage Isomerizations of Ruthenium (II) Complexes Having Nitrosyl as a Spectator Ligand Article Nov 1995 Dai Ooyama Noriharu Nagao Hirotaka Nagao Koji Two examples are the red nitrito complex [Co (NH 3) 5 (ONO)] 2+ is metastable, isomerizing to the yellow nitro complex [Co (NH 3) 5 (NO 2)] 2+. Jul 31, 2021 · Preparation of Nitro Compounds Nitro compounds can be prepared in a number of ways, including the direct substitution of hydrocarbons with nitric acid, (24. [11] [LnMNO2]− + H+ → [LnMNO]+ + OH− The reaction is reversible in some cases. , 2002). 56 (A) mono nitro-to-nitrito; (B) bis nitro-to-nitrito; (C) bis nitro-to-nitrito and effects of metal substitution on yields. The nitrite ligand can link to metals through the N atom (“nitro” complexes) or the O atom (“nitrito” complexes) (see below). However, quite recently, Warren et al. 2) RX + NO A 2 → RNO A 2 + X and by oxidation of primary amines, (24. The N-bonded nitro group is usually described as a strong field ligand. The higher stability of the nitro isomer in comparison to the nitrito isomer has been substantiated. Sep 1, 2018 · The nitrito would undergo rapid decomposition (releasing HNO2) to form a vinyl nitro product (Fig. r. 1B–c), and iii) oxidation of the NO2 -cLA radical intermediate to a nitro-peroxy followed by reduction of the peroxy to an alkoxy radical mediated by the oxidation of • NO to • NO 2. They are further classified as aliphatic or aromatic nitro compounds, depending upon whether the nitro group is bonded to an alkyl or aryl group. Nitrito- Linkage Isomers The cationic cobalt complex [Co (NH 3) 5 (NO 2)]Cl 2 exists in two separable linkage isomers of the complex ion: (NH 3) 5 (NO 2)] 2+. The mechanism of reaction will in both cases go through the o -bonded isomer (the nitrito- isomer), May 13, 2021 · Nitro-nitrito metal complexes can be regarded as good examples of linkage isomerism. proposed a mechanism according to which the nitro isomer transforms to the exo-nitrito form first, and subsequently converts to the final photoproduct, the endo-nitrito isomer. Jan 20, 2001 · The mechanism of formation of nitro derivatives in the case of aquopentamminecobalt (III) and cis-nitroaquobis- (ethyl-enediamine)-cobalt (III) ions in weakly acid solutions of nitrite ion is Sep 30, 1998 · The O-bound nitrito complexes isomerize spontaneously and stereoretentively [2] to the more stable N-bound nitro complexes, both in the solid state 3, 4 and in solution 5, 6, 7, 8, 9, 10. Jan 8, 2015 · It is well-known that octahedral nitro complexes of Co (III), Rh (III) and Ir (III) are thermodynamically favored over nitrito ones [3] and an intramolecular nitrito–nitro linkage isomerization occurs spontaneously in solution and even in the solid state [4]. Jan 1, 1989 · The spectra were recorded in the form of KBr or polyethylene discs. Oct 26, 2025 · Based on the kinetic parameters, the exo -nitrito isomer is slightly less stable for Ni-4d'. Jan 30, 2004 · Both nitro to nitrito and reverse reactions obey first order kinetic law in solid state. Apr 4, 2014 · The solid-state, low-temperature linkage isomerism in a series of five square planar group 10 phosphino nitro complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modelling. In this work, we report for the first time the experimental evidence of the earlier theoretically predicted nitro-to- endo -nitrito mechanism via the exo -nitrito form for square-planar nickel- (II) nitrite coordination compounds in the solid state. May 24, 2012 · So, as opposed to previous reports concerning formation of a seven-coordinate activated complex in nitro/nitrito isomerization of pentaamminecobalt (III) [16, 35], we could assign a dissociative mechanism to the interconversion of above mentioned linkage isomers. Explanations for that behaviour are likely to involve the high oxophilicity of silicon. Thus, one can generate nitrito complexes by base-hydrolysis of electrophilic metal nitrosyls. In this work, we report for the first time the experimental evidence of the earlier theoretically predicted nitro-to- endo -nitrito mechanism via the exo -nitrito form for square-planar nickel (II) nitrite coordination compounds in the solid state. In aqueous solution the isomerization of nitrito to nitro is very similar to that for the parent pentaamine while in the solid phase it is retarded. dgankhdjsfrufbbmrouspizklaihywjujwyxielujkebovostkbztudqgxdwcctmdxdywuxrwyxqlvyun