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• NO disproportionates on stoichiometric ceria to nitrites and trans -hyponitrites. • NO + O 2 coadsorption on ceria leads to formation of different surface nitrates. • NO interacts with reduced ceria forming NO2− and N 3 - species. • The NO2− species interact with NO to produce hyponitrites. • Azide species demonstrate properties very similar to those of surface isocyanates. Cerium is a key component in many DeNO x catalysts. An important property of ceria related to these applications is its high oxygen storage capacity. Indeed, in some reaction steps, cerium switches its oxidation state between 3+ and 4 +. To design new and effective cerium-based DeNOx catalysts, it is necessary to know in details the interaction between CeO 2-x and nitrogen oxides. One of the most informative techniques in this respect is IR spectroscopy. There are many IR studies devoted to this problem. However, as a rule, the efforts are concentrated on investigation of the oxidized forms of ceria and there are few works dealing with reduced oxide. There are also many contradictory assignments and few works use isotopic labelling for better interpretation of the spectra. Here we report a summary of our IR studies on the interaction of nitrogen oxides with ceria paying equal attention to the reduced and non-reduced oxide form. To strengthen the assignments we have used isotopically labelled molecules and DFT calculation. It was found that the initial stages of interaction of NO with oxidized ceria comprise NO disproportionation to symmetric nitrites (formal oxidation state of nitrogen 3+) and hyponitrites (formal oxidation state of nitrogen 1+). At further stages non-symmetric nitrites and N 2 O are also formed. In presence of oxygen all these species are converted into surface nitrates. Adsorption of N 2 O on reduced ceria is dissociative and leads to formation of N 2 with simultaneous filling the oxygen vacancies and oxidation of Ce3+. Initial stages of interaction of reduced ceria with NO includes (i) formation of surface azides (N 3 −, showing remarkable similarity with NCO− species) and NO2−. The latter species interact with additional NO molecule being thus converted into hyponitrites. Further stages are associated with formation of nitrites, and, in presence of O 2 , nitrates. [ABSTRACT FROM AUTHOR]

Reductive coupling of nitric oxide (NO) to give N2O is an important reaction in the global nitrogen cycle. Here, a dinickel(II) dihydride complex 1 that releases H2 upon substrate binding and serves as a masked dinickel(I) scaffold is shown to reductively couple two molecules of NO within the bimetallic cleft. The resulting hyponitrite complex 2 features an unprecedented cis‐[N2O2]2− binding mode that has been computationally proposed as a key intermediate in flavodiiron nitric oxide reductases (FNORs). NMR and DFT evidence indicate facile rotational fluxionality of the [N2O2]2− unit, which allows to access an isomer that is prone to N2O release. Protonation of 2 is now found to trigger rapid N2O evolution and formation of a hydroxido bridged complex, reminiscent of FNOR reactivity. This work provides fundamental insight into the biologically relevant reductive coupling of two NO molecules and the subsequent trajectory towards N2O formation at bimetallic sites. Emulated reaction trajectory: Two NO molecules are reductively coupled at a dinickel(II) dihydride complex that serves as a dinickel(I) synthon via substrate induced H2 release. The resulting cis‐hyponitrite adopts an unusual N,O‐bridging binding mode in solid state, but facile rotational fluxionality within the bimetallic cleft allows to access an isomer that is prone to proton‐triggered N2O formation. [ABSTRACT FROM AUTHOR]

Abstract Cytochrome c oxidases (C c O) reduce O 2 to H 2 O in the respiratory chain of mitochondria and many aerobic bacteria. In addition, some species of C c O can also reduce NO to N 2 O and water while others cannot. Here, the mechanism for NO-reduction in C c O is investigated using quantum mechanical calculations. Comparison is made to the corresponding reaction in a "true" cytochrome c -dependent NO reductase (c NOR). The calculations show that in c NOR, where the reduction potentials are low, the toxic NO molecules are rapidly reduced, while the higher reduction potentials in C c O lead to a slower or even impossible reaction, consistent with experimental observations. In both enzymes the reaction is initiated by addition of two NO molecules to the reduced active site, forming a hyponitrite intermediate. In c NOR, N 2 O can then be formed using only the active-site electrons. In contrast, in C c O, one proton-coupled reduction step most likely has to occur before N 2 O can be formed, and furthermore, proton transfer is most likely rate-limiting. This can explain why different C c O species with the same heme a 3 -Cu active site differ with respect to NO reduction efficiency, since they have a varying number and/or properties of proton channels. Finally, the calculations also indicate that a conserved active site valine plays a role in reducing the rate of NO reduction in C c O. Graphical Abstract Highlights • Mechanisms for NO reduction in C c Os with a heme a 3 active site are studied. • Free energy profiles are constructed combining computational and experimental data. • Comparisons are made to the mechanism for NO reduction in cNOR. • High reduction potentials in C c Os are found to cause low rates of NO disappearance. • A conserved valine may play a role in reducing the NO reduction rate in C c O. [ABSTRACT FROM AUTHOR]

This study investigated nitrite (NO2−) accumulation due to FA (Free Ammonia: NH3) inhibition in an anaerobic-aerobic-anoxic (AOA) process reactor to mainly treat wastewater containing 302−610 mg/L of NH3/NH4+-N. Based on an experimental operation focusing on the nitrification, it was observed that NO2− was accumulated in the aerobic nitrification zone as pH increased, due to inhibition of NO2− conversion to NO3− by FA. This result implied FA inhibition to NOB (NO2−−Oxidizing Bacteria) for converting NO2− to NO3−. The objective of this study is to develop a feasible monitoring procedure for early detection of the FA inhibition toward NO2− accumulation and poor nitrification. Thus, in order to rapidly assess FA concentrations, an NH3 probe was utilized to measure NH3 concentrations together with applying a simple model prediction using the measured NH4+ concentrations, the Henry’s law constant of NH3 and measured pH. The predictive model NH3 levels were verified by a good correlation (89%) with the corresponding measured data, but the model prediction underestimated FA concentrations at less than 7.4 and a little overestimated at pH above 7.5. Interestingly, accumulated NO2− levels were roughly correlated with FA levels that were observed at delayed time points. This reflects the detected FA levels can be good indicators of NO2− levels with some delayed time. NO2− accumulation started at measured FA concentrations of higher than approximately 3 mg/L and ceased below that FA level. [ABSTRACT FROM AUTHOR]

The synthesis, structure, and magnetic properties of two mononuclear cobalt(ii) complexes [Co(LSal,2-Ph)2] (1) and [Co(LNph,2-Ph)2] (2) are reported. The utilized sterically demanding Schiff-base ligands HLSal,2-Ph (2-(([1,1′-biphenyl]-2-ylimino)methyl)phenol) and HLNph,2-Ph (1-(([1,1′-biphenyl]-2-ylimino)methyl)naphthalen-2-ol) lead to a strong distortion of the [N2O2] coordination environment in the complexes 1 and 2, which can be primarily attributed to the variation in the dihedral angle between the planes of the two chelate ligands. Magnetic susceptibility and FD-FT THz-EPR measurements as well as ab initio calculations reveal that both complexes exhibit an easy-axis type of anisotropy. For both compounds frequency-dependent ac susceptibility measurements show an out-of-phase susceptibility under applied static fields of 400 and 1000 Oe. A detailed analysis of the underlying relaxation process is given, revealing significant differences in the contributions of Orbach, Raman, and direct processes within the observed temperature range. Fitting of the magnetic data leads to a spin-reversal barrier of 49 cm−1 for 1 at an applied field of 1000 Oe. For 2 the barrier is not well defined by the analysis of the relaxation times and is, therefore, approximated by the experimental barrier derived from FD-FT THz-EPR measurements (62.8 cm−1). The results from ab initio calculations and FD-FT THz-EPR measurements show that the distortion of the coordination sphere in complexes 1 and 2 from the pseudotetrahedral towards a square-planar coordination geometry leads to an increase in both the axial (D) and the rhombic zero-field splitting (E). [ABSTRACT FROM AUTHOR]

[Display omitted] • When adsorbed on ceria NO initially disproportionates to nitrites and hyponitrites. • Further NO adsorption includes formation of non-symmetric nitrites and N 2 O. • Hyponitrites are very easily oxidized when dosing O 2 to the NO/CeO 2 system. • Nitrites first develop and are then oxidized when dosing O 2 to the NO/CeO 2 system. Adsorption of NO and co-adsorption of NO and O 2 on ceria have been re-investigated by FTIR spectroscopy. To provide unambiguous assignments of the IR bands, adsorption of 15NO and co-adsorption of 14NO + 15NO isotopic mixtures have also been studied and DFT calculations performed. At the initial adsorption stages mainly symmetric nitrite species (2472, 1304, ca. 1160 and 822 cm‐1) and trans- hyponitrites ([N 2 O 2 ]2−, ca. 1100 cm‐1) are simultaneously produced as a result of NO disproportionation. At further stages non-symmetric NO 2 − species (1393 and 1014 cm‐1), N 2 O (2240, 1252 cm‐1) and small amount of nitrates are formed. Nitrates are the only surface products of the thermal decomposition of the nitrites and hyponitrites. In the presence of small amounts of oxygen, the hyponitrites are very easily oxidized. In contrast, all nitrites increase in concentration after addition of small amount of O 2 to the NO/CeO 2 system but are gradually oxidized in the presence of higher amount of oxygen giving rise to different surface nitrates. [ABSTRACT FROM AUTHOR]

A copper complex, [CuI(tmpa)(MeCN)]+, effectively reductively couples NO(g) at RT in methanol (MeOH), giving a structurally characterized hyponitritodicopper(II) adduct. Hydrogen-bonding from MeOH is critical for the hyponitrite complex formation and stabilization. This complex exhibits the reverse redox process in aprotic solvents, giving CuI + NO(g), leading to CuI-mediated NO(g)-disproportionation. The relationship of this chemistry to biological iron and/or copper mediated NO(g) reductive coupling to give N2O(g) is discussed. [ABSTRACT FROM AUTHOR]

Support-free interconnected Pt nanowire networks (Pt NWNs) were fabricated by rapidly pouring sodium borohydride (NaBH4) solution into the Pt precursor solution, where hydrogen bubbles were in situ generated from hydrolysis and oxidation of NaBH4 as a dynamic template. There was no any capping agent, surfactant, seed, polymer, or special experimental device involved. The morphology, composition and structure of the samples were mainly characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The architectures displayed highly electrocatalytic behavior toward nitrite oxidation and wide linear ranges of 1.0 μM-24.0 mM and 24.0-132.0 mM, together with high sensitivity (16.94 and 4.34 μA mM-1) and low detection limit (0.14 μM, S/N = 3). It demonstrated the improved electroanalytical performance for nitrite determination because of the unique free-standing Pt nanostructures with clean surfaces. [ABSTRACT FROM AUTHOR]

The solid state photolysis of sodium, silver and thallium hyponitrite (M 2 N 2 O 2 , M = Na, Ag, Tl) salts and a binuclear complex of cobalt bridged by hyponitrite ([Co(NH 3 ) 5 -N(O)-NO-Co(NH 3 ) 5 ] 4 + ) were studied by irradiation with visible and UV light in the electronic absorption region. The UV–visible spectra for free hyponitrite ion and binuclear complex of cobalt were interpreted in terms of Density Functional Theory calculations in order to explain photolysis behavior. The photolysis of each compound depends selectively on the irradiation wavelength. Irradiation with 340–460 nm light and with the 488 nm laser line generates photolysis only in silver and thallium hyponitrite salts, while 253.7 nm light photolyzed all the studied compounds. Infrared spectroscopy was used to follow the photolysis process and to identify the generated products. Remarkably, gaseous N 2 O was detected after photolysis in the infrared spectra of sodium, silver, and thallium hyponitrite KBr pellets. The spectra for [Co(NH 3 ) 5 -N(O)-NO-Co(NH 3 ) 5 ] 4 + suggest that one cobalt ion remains bonded to N 2 O from which the generation of a [(NH 3 ) 5 CoNNO] + 3 complex is inferred. Density Functional Theory (DFT) based calculations confirm the stability of this last complex and provide the theoretical data which are used in the interpretation of the electronic spectra of the hyponitrite ion and the cobalt binuclear complex and thus in the elucidation of their photolysis behavior. Carbonate ion is also detected after photolysis in all studied compounds, presumably due to the reaction of atmospheric CO 2 with the microcrystal surface reaction products. Kinetic measurements for the photolysis of the binuclear complex suggest a first order law for the intensity decay of the hyponitrite IR bands and for the intensity increase in the N 2 O generation. Predicted and experimental data are in very good agreement. [ABSTRACT FROM AUTHOR]

A method for the determination of nitrite in soil and vegetable samples by UV-Vis spectroscopy was proposed. The kinetic UV-Vis data were collected during the reaction between nitrite and 4-amino-3-hydroxynaphthalene-1-sulfonic acid with concentration of 0.001 M and pH 1.6. Data were collected by standard addition method. Multivariate curve resolution-alternating least squares was employed to analyze data with non-negativity and three-way data structure constraints. The method can be used to solve matrix effect and unknown interferents in the determination of nitrite in complex samples. The proposed method was used to determine nitrite at low mg/L levels with satisfactory results in soil, lettuce, cabbage and cucumber samples. [ABSTRACT FROM AUTHOR]

Heme-hyponitrites are intermediates that form at the bimetallic active sites of bacterial nitric oxide reductases. To probe a possible effect of the Fe–Fe distance on hyponitrite stability, we prepared a bridged bis-porphyrin Fe-hyponitrite compound, namely [(OEP-CH 2 )Fe] 2 ( μ 2 ,η 1 , η 1 -ONNO). Its υ NO of 992 cm −1 (υ 15NO of 976 cm −1 ) is close to the υ NO of 983 cm −1 reported previously by us for the crystallographically characterized [(OEP)Fe] 2 ( μ 2 ,η 1 , η 1 -ONNO) compound. The bridged bis-porphyrin Fe-hyponitrite complex is unstable with respect to N 2 O production, supporting the role of the bis-Fe porphyrin system in hyponitrite conversion to N 2 O. The preparation and crystallographic determination of the bridging sulfato derivative is also reported. [ABSTRACT FROM AUTHOR]

Herein, we review the preparation and coordination chemistry of cis and trans isomers of hyponitrite, [N2O2]2–. Hyponitrite is known to bind to metals via a variety of bonding modes. In fact, at least eight different bonding modes have been observed, which is remarkable for such a simple ligand. More importantly, it is apparent that the cis isomer of hyponitrite is more reactive than the trans isomer because the barrier of N2O elimination from cis-hyponitrite is lower than that of trans-hyponitrite. This observation may have important mechanistic implications for both heterogeneous NOx reduction catalysts and NO reductase. However, our understanding of the hyponitrite ligand has been limited by the lack of a general route to this fragment, and most instances of its formation have been serendipitous. [ABSTRACT FROM AUTHOR]

To design new deNO x materials and processes we need to know in details the mechanism of NO interaction with solid surfaces. Many NO x conversion catalysts contain ceria as a component and cerium changes its oxidation state in the course of redox catalytic processes. Here we show that the interaction between NO and reduced ceria leads to formation of azides (N 3 − , 2044–2042 cm −1 ) and nitric oxide dianion (NO 2− , 1010–980 cm −1 ) with the simultaneous oxidation of Ce 3+ . These species are established for the first time after NO adsorption on solid surfaces and their relative concentrations strongly depend on the sample morphology. At ambient temperature N 3 − does not interact with NO or O 2 alone but easily disappears in the co-presence of the two gases, thus demonstrating reactivity similar to that of isocyanates. In contrast, NO 2− accepts one NO molecule and is converted into hyponitrite (bands in the 1030–970 cm −1 region). At further stages of interaction, N 2 O, N 2 , nitrites and nitrates are formed. The present findings enrich the current opinions of catalytic NO conversion and impose some revisions. [ABSTRACT FROM AUTHOR]

For the (aut)oxidation of toluene to benzyl hydroperoxide, benzyl alcohol, benzaldehyde, and benzoic acid, the thermochemical profiles for various radical-generating reactions have been compared. A key intermediate in all of these reactions is benzyl hydroperoxide, the heat of formation of which has been estimated by using results from CBS-QB3, G4, and G3B3 calculations. Homolytic OO bond cleavage in this hydroperoxide is strongly endothermic and thus unlikely to contribute significantly to initiation processes. In terms of reaction enthalpies the most favorable initiation process involves bimolecular reaction of benzyl hydroperoxide to yield hydroxy and benzyloxy radicals along with water and benzaldehyde. The reaction enthalpy and free energy of this process is significantly more favorable than those for the unimolecular dissociation of known radical initiators, such as dibenzoylperoxide or dibenzylhyponitrite. [ABSTRACT FROM AUTHOR]

The azo-dye Schiff's base of N2O2 dibasic ligand, H2L [N,N'-bis(5-(4-sulfanilamidophenylazosalicylidene)ethylenediamine] was prepared by the condensation of ethylenediamine with [5-(4-sulfanilamidophenylazo-salicylaldehyde] in ethanol. New complexes of with metal ions Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Pt(IV), Fe(III) and Cr(III) are synthesized. Elemental, spectroscopic and thermal analyses as well as conductivity and magnetic susceptibility measurements are used to elucidate the structure of the newly prepared metal complexes. The azo-dye Schiff's base behaves as a di-negative N2O2 tetradentate ligand. The metal complexes exhibited square planar, tetrahedral and octahedral geometrical arrangements, the molar conductivity data indicates that all complexes are neutral. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the Cu(II), Mn(II), Cr(III) and Co(II) complexes were carried out in the range of 30-800 °C. The complexes were decomposed in one and two stages of the Cu(II), Mn(II), Cr(III) and Co(II) complexes, respectively. Also, decomposition of the synthesized complexes is related to the Schiff's base characteristics. The thermal decomposition of the studied reactions was first order. The kinetic parameters for the decomposition steps in Cu(II), Mn(II), Cr(III) and Co(II) complexes thermograms have been calculated using Broido's method. In molecular modeling the geometries of azo-dye Schiff base ligand H2L and its metal(II/III/IV) complexes were fully optimized with respect to the energy using the 6-31G basis set. Antimicrobial activities of the azo-dye Schiff's base ligand and its corresponding metal complexes were screened against various organisms. The azo-dye Schiff's base ligand and some of its complexes were found to be biologically inactive. [ABSTRACT FROM AUTHOR]

The detoxification of nitric oxide (NO) by bacterial NO reductase (NorBC) represents a paradigm of how NO can be detoxified anaerobically in cells. In order to elucidate the mechanism of this enzyme, model complexes provide a convenient means to assess potential reaction intermediates. In particular, there have been many proposed mechanisms that invoke the formation of a hyponitrite bridge between the heme b3 and nonheme iron (FeB) centers within the NorBC active site. However, the reactivity of bridged iron hyponitrite complexes has not been investigated much in the literature. The model complex {[Fe(OEP)]2(μ-N2O2)} offers a unique opportunity to study the electronic structure and reactivity of such a hyponitrite-bridged complex. Here we report the detailed characterization of {[Fe(OEP)]2(μ-N2O2)} using a combination of IR, nuclear resonance vibrational spectroscopy, electron paramagnetic resonance, and magnetic circular dichroism spectroscopy along with SQUID magnetometry. These results show that the ground-state electronic structure of this complex is best described as having two intermediate-spin (S = 3/2) iron centers that are weakly antiferromagnetically coupled across the N2O22- bridge. The analogous complex {[Fe(PPDME)]2(μ-N2O2)} shows overall similar properties. Finally, we report the unexpected reaction of {[Fe(OEP)]2(μ-N2O2)} in the presence and absence of 1-methylimidizole to yield [Fe(OEP)(NO)]. Density functional theory calculations are used to rationalize why {[Fe(OEP)]2(μ-N2O2)} cannot be formed directly by dimerization of [Fe(OEP)(NO)] and why only the reverse reaction is observed experimentally. These results thus provide insight into the general reactivity of hyponitrite-bridged iron complexes with general relevance for the N-N bond-forming step in NorBC. [ABSTRACT FROM AUTHOR]

Highlights: [•] New dipodal s-triazine based Schiff base was synthesized. [•] Six complexes involved Schiff bases with triazine have been synthesized. [•] The ligand and complexes were characterized. [•] The magnetic data for the complexes were showed the high-spin. [Copyright &y& Elsevier]

The remediation of nitrate-contaminated water using electrochemical reduction at a tin cathode has previously been shown to give almost quantitative denitrification (removal of dissolved nitrogen species) under highly cathodic polarization. A particular focus of this project was to identify specific role(s) for tin in the reaction in the context of the previous literature. The current efficiency for denitrification was enhanced in alkaline solution, and the reaction was accelerated by the presence of small concentrations of Sn(II) salts, which are in a dynamic exchange between cathodic deposition and corrosion of the cathode. Literature precedent indicates that Sn(II) salts promote the 'dimerization' pathway of NO to hyponitrite in preference to reduction to ammonia. Hyponitrite is a known intermediate in the electrochemical reduction of nitrate, but its spontaneous decomposition gives predominantly N2O, which does not reduce further to N2. We have shown that hyponitrite is reduced electrochemically in competition with its thermal decomposition, which provides a pathway to N2 via the spontaneous dehydration of HO−NH−NH−OH. The possible role of surface-bound Sn−H species in the reduction mechanism is discussed, but further work is needed to substantiate this proposal. [ABSTRACT FROM AUTHOR]

The catalytic mechanism of reduction of NO to N2O in the bacterial enzyme nitric oxide reductase has been investigated using hybrid density functional theory and a model of the binuclear center (BNC) based on the newly determined crystal structure. The calculations strongly suggest a so-called cis:b3 mechanism, while the commonly suggested trans mechanism is found to be energetically unfavorable. The mechanism suggested here involves a stable cis-hyponitrite, and it is shown that from this intermediate one N-O bond can be cleaved without the transfer of a proton or an electron into the binuclear active site, in agreement with experimental observations. The fully oxidized intermediate in the catalytic cycle and the resting form of the enzyme are suggested to have an oxo-bridged BNC with two high-spin ferric irons antiferromagnetically coupled. Both steps of reduction of the BNC after N2O formation are found to be pH-dependent, also in agreement with experiment. Finally, it is found that the oxo bridge in the oxidized BNC can react with NO to give nitrite, which explains the experimental observations that the fully oxidized enzyme reacts with NO, and most likely also the observed substrate inhibition at higher NO concentrations. [ABSTRACT FROM AUTHOR]

Abstract: Nitric oxide reductase (NOR) type reactions (2NO+2e− +2H+ →N2O+H2O) on transition metal complexes not involving NO disproportionation (3NO→N2O+NO2) are reviewed. The former has little reported, although the latter is very common reaction. The formation of N2O indicates that N–N coupling of two NO molecules is an essential step. A few examples of N–N coupling on transition metal complexes have been structurally characterized, including several examples of hyponitrite (O–NO)2− complexes and only one diruthenium complex bearing neutral (ONg mode. Protonation or heating their complexes led to elimination of N2O. In the examination of the NOR-type reaction, only a few functional model complexes for the active site of the metalloenzyme have been developed. These complexes also showed NOR activity. Finally, an NO reduction cycle in the diruthenium system is described. [Copyright &y& Elsevier]

The reaction of the electronically and coordinatively unsaturated compounds [Ru2(CO)4(μ-H)(μ-PBut2)(μ-L2)] (1) (RuᆖRu) with nitric oxide afforded four new trans-hyponitrito complexes of the general formula [Ru2(CO)4(μ-H)(μ-PBut2)(μ-L2)(μ-η2-ONNO)] (2) in good yields. Thus the complexes 2a–e were obtained using the following bridging biphosphane ligands (μ-L2): dppm (2a, dppm = Ph2PCH2PPh2), dppen (2b, dppen = Ph2PC(ᆖCH2)PPh2), dpppha (2c, dpppha = Ph2PN(Ph)PPh2), dpppra (2d, dpppra = Ph2PN(Prn)PPh2), and dppbza (2e, dppbza = Ph2PN(CH2Ph)PPh2). The molecular structures of the complexes 2a–e were determined by X-ray diffraction. Furthermore the molecular structure of the known compound 2a was reinvestigated in light of a better refinement of the short intramolecular contact between the hyponitrite O atom in close vicinity to the C atom of a neighbouring carbonyl group. This unusual effect in crystals of all compounds 2a–e can be interpreted as a nucleophilic intramolecular attack of a hyponitrito ligand towards an electrophilic carbon center of a carbonyl ligand. [ABSTRACT FROM AUTHOR]

The nitrogen cycle is a process in nature to sustain a living environment. A nitric‐oxide‐to‐nitrous‐oxide step via hyponitrite is easily modeled with marbles but hardly substantiated in its details. There are many hypotheses around the tentative, highly reactive hyponitrite intermediate and its coordination to the iron atoms in the active site of nitric‐oxide reductase. Now, another puzzle piece was obtained by the synthesis and characterization of mononuclear ruthenium complexes, which show the hyponitrite intermediate in its partly protonated HN2O2− form. As opposed to its reactivity in the catalytic cycle, trans‐hydrogenhyponitrite, a weak‐field ligand, reveals itself to be stable in the ruthenium environment. For more information, see the Full Paper by P. Klüfers and D. Beck on page 16019 ff. [ABSTRACT FROM AUTHOR]

Review: preparation and coordination chemsitry of cis and trans N2O22-; 118 refs. [ABSTRACT FROM AUTHOR]