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Among the isoelectronic ligands CN-, CO, and NO+, an oblique bonding to the metal is well-established for the nitrosyl ligand, with M-N-O angles down to ≈120°. In the last decades, the nitrosyl community got into the habit of addressing a bent-bonded nitrosyl ligand as 1NO-. Thus, because various redox forms of a nitrosyl ligand seem to exist, the ligand is considered to be "noninnocent" because of the obvious ambiguity of an oxidation state (OS) assignment of the ligand and metal. Among the bent-bonded species, the low-spin {CoNO}8 class is prototypic. From this class, some 20 new nitrosyl compounds, the X-ray structure determinations of which comply with strict quality criteria, were analyzed with respect to the OS issue. As a result, the effective OS method shows a low-spin d8 CoI-NO+ couple instead of a negative OS of the ligand at the BP86/def2-TZVP (+D3, +CPCM with infinite permittivity) level of theory. The same holds for some new members of the linear subclass of {CoNO}8 compounds. For all compounds, a largely invariable "real" charge of ≈ -0.3 e was obtained from population analyses. All of these electron-rich d8 species strive to manage Pauli repulsion between the metal electrons and the lone pair at the nitrosyl's nitrogen atom, with the bending of the CoNO unit as the most frequent escape.

Nitrosyl–metal bonding relies on the two interactions between the pair of N–O‐π* and two of the metal's d orbitals. These (back)bonds are largely covalent, which makes their allocation in the course of an oxidation‐state determination ambiguous. However, apart from M‐N‐O‐angle or net‐charge considerations, IUPAC′s “ionic approximation” is a useful tool to reliably classify nitrosyl metal complexes in an orbital‐centered approach., “The MNO segment should be linear for NO + but bent for NO − ”: Though this statement is taken from a IUPAC publication on oxidation states (OS), it mirrors a common belief. However, deriving the OS by the effective‐oxidation‐state procedure (EOS), the new nitrosylcobalt species (see the Figure) resembled a CoI(NO+) couple instead of the expected CoIII(NO−).

Aquest mateix article està publicat en anglès a: 'Angewandte Chemie International Edition' (ISSN 1433-7851, EISSN 1521-3773), 2020, vol. 59, núm. 30, p. 12381-12386. DOI https://doi.org/10.1002/anie.202003122 Publisher Note for articles published since 1962: This is the German version of Angewandte Chemie. Do not cite this version alone. Take the reference of the International Edition version Nitrosyl–metal bonding relies on the two interactions between the pair of N–O‐π* and two of the metal's d orbitals. These (back)bonds are largely covalent, which makes their allocation in the course of an oxidation‐state determination ambiguous. However, apart from M‐N‐O‐angle or net‐charge considerations, IUPAC′s “ionic approximation” is a useful tool to reliably classify nitrosyl metal complexes in an orbital‐centered approach The MNO segment should be linear for NO+ but bent for NO−“: Diese Aussage entstammt zwar einer IUPAC‐Publikation zu Oxidationstufen (OS), spiegelt zugleich aber eine verbreitete Meinung wider. Die Herleitung der OS durch den EOS‐Algorithmus führt jedoch für eine neue Nitrosylcobalt‐Spezies (siehe Bild) zu einem CoI(NO+)‐Paar anstelle der erwarteten CoIII(NO−)‐Formulierung Deutsche Forschungsgemeinschaft. Grant Number: KL 624/18-1 Ministerio de Ciencia, Innovación y Universidades. Grant Number: PGC2018-098212-B-C22

A conspicuous detail of the so‐called brown‐ring test (the analytical test on nitrate) is the reddish color of the bottom layer of concentrated sulfuric acid, which develops upon the bleeding of the brown layer into the acid. Crystals of the same color form from a solution of ferrous sulfate in concentrated sulfuric acid on saturation with gaseous nitric oxide. The structure of this H3O[{Fe(NO)(μ4‐SO4)(μ2‐SO4)0.5}n/n] (1a) is made up from infinite chessboard‐type layers with sulfur on the field junctions and Fe(NO) moieties below the black and above the white fields. An Fe–N–O angle of about 160° causes disorder in the tetragonal space group I4/mmm. A similar crystal pathology was found in the related [{Fe(MeOH)(NO)(μ4‐SO4)}n/n] (1b) in the same crystal class. A one‐dimensional coordination polymer is formed in crystals of a third compound that comprises the Fe(NO)O5 coordination pattern, namely the brown oxalato species [{Fe(H2O)(NO)(μ2‐ox)}n/n·H2O] (2). A still larger NO tilt of about 156° is not obscured by disorder in the triclinic crystals of 2.

Although the "brown-ring" ion, [Fe(H2 O)5 (NO)]2+ (1), has been a research target for more than a century, this poorly stable species had never been isolated. We now report on the synthesis of crystals of a salt of 1 which allowed us to tackle the unique bonding situation on an experimental basis. As a result of the bonding analysis, two stretched, spin-polarised π-interactions provide the Fe-NO binding-and challenge the concept of "oxidation state".

International audience; Mononitrosyliron compounds (MNICs) of the Enemark-Feltham {FeNO} 7 type divide into a dublet (S = 1/2) and a quartet (S = 3/2) spin variant. The latter relies on weak-field coligands such as aminecarboxylates. Aqua-only co-ligation appears to exist in the long-known 'brown-ring' [Fe(H 2 O) 5 (NO)] 2+ cation which was prepared originally from ferrous salts and NO in sulfuric acid. A chloride variant of this species, the green [FeCl 3 (NO)] − ion, was first prepared analoguosly by using hydrochloric instead of sulfuric acid. As a tetrahedral species, it is the simple prototype of sulfur-bonded {FeNO} 7 (S = 3/2) MNICs of biological significance. Though being investigated for more than a century, neither clean preparative routes nor reliable structural parameters were available for the [FeCl 3 (NO)] − ion and related species such as the [FeCl 2 (NO) 2 ] − ion, a prototypical dinitrosyliron species (a 'DNIC'). In this work, both issues have been resolved. In addition, we report on a computational study on the ground-and excited-state properties including an assignment of the chromophoric transitions. Photoinduced metastable isomers were characterised in a combined experimental and computational approach which resulted in the confirmation of a single photoinduced linkage isomer of the paramagnetic nitrosyl-metal coordination entity.

A joint approach of chemists, mathematicians and engineers in the field of chemical reaction enhanced gas-liquid mass transfer on single bubbles is presented. New chemical systems are developed for homogenous chemical reactions in the liquid. By applying different metal-complex based reaction systems with diverse ligands in different reaction media (water and organic solvents) a broad range of reaction kinetics is available. As one measure, the bubble size change over time is investigated. The shrinking of the bubble allows the determination of overall mass transfer rates under diverse conditions. Numerous groups investigated the wake region of the bubble. The influence of the mixing behavior in this region on the mass transfer in general but also, e.g., on competitive consecutive chemical reactions is visualized. For a deeper understanding of the effect of surfactants on mass transfer, simulations are performed providing a high temporal and spatial resolution of the flow and concentration field near the bubbles surface. Furthermore, a compartment model for the description of the mass transfer near a single bubble is developed which allows the calculation of competitive consecutive chemical reactions with reasonable numerical effort.

Reactive bubbly flows are found in many chemical and biochemical process-es. They are characterized by complex hydrodynamics that govern global mass transfer and reaction rates. Effects, which have to be taken into account when modelling and simulating the reaction progress are enhanced bubble-bubble interaction and bubble-induced turbulence as well as swarm-induced macro-convection. This poses great challenges on both, experimental analysis and numerical simulation. Bubble swarms at higher gas fractions are opaque, which limits the use of optical flow measurement techniques. Moreover, simu-lations at industrial scale are only feasible with point-bubble-based Euler-Euler or Euler-Lagrange approaches. Such approaches require closure relations, which account for all relevant interfacial forces as well as bubble-induced tur-bulence and coalescence including swarm effects. This chapter describes the progress in the experimental analysis and CFD simulation of reactive bubbly flows achieved during the time of the DFG Priority Programme SPP 1740. Ex-perimental studies in bubble columns reported in this Chapter were carried out at TU Dresden and OVGU Magdeburg. CFD model development and simula-tion has been carried out at OVGU Magdeburg using the Euler-Euler and Euler-Lagrange method and at TU Kaiserslautern and Helmholtz-Zentrum Dresden-Rossendorf using the Euler-Euler approach. As reaction systems the chemi-sorption of CO2 in NaOH solution and the reaction of FeII(edta) with NO were studied.

The chemistry of non-heme iron centres with the ‘non-innocent’ NO ligand has experienced a renaissance in the last decades because of findings of their biochemical significance. Our work concentrates on high-spin {FeNO}7 complexes which show an S = 3/2 ground state, and their related {Fe(NO)2}9 species. Crystalline complexes were prepared from the reaction of NO with FeII and thoroughly characterized. Bonding, spin situation and oxidation states of the Fe–NO moiety are described. Using quantum-chemical calculations like DFT, CASSCF and EOS, frontier orbitals and spin populations of selected complexes are given. The results are leading to the interpretation of a largely covalent nature of the nitrosyl–iron bond. The investigation of the [Fe(H2O)5(NO)]2+ ion, an enduring issue in Inorganic Chemistry since the nineteenth century, lead to the isolation of a gallate or ferrate salt of the general formula [Fe(H2O)5(NO)][MIII(fpin)2(H2O)]2·xH2O (M = Fe, Ga; x ≈ 8.3). Crystal structure analyses of halogenido-mononitrosyliron compounds (MNICs) and their dinitrosyl analogues (DNICs) are presented. The reaction process is analysed by in situ-UV–vis and in situ-IR measurements. Their application as a competitive-consecutive reaction pattern for engineer partners is introduced. Crystal-structure analyses and the calculation of the electronic properties for nitrosyl-iron compounds with different aminecarboxylato co-ligands like imino- and oxodiacetate as well as ethylenediaminetetraacetate (edta) enable a closer insight towards their structure-properties relationship.

Taylor bubbles are bubbles that are filling a capillary fixed or rising in a liquid flow. Due to their well-defined size, shape and velocity the flow field around Taylor bubbles is well controllable. Furthermore, only a small amount of gas and liquid is required for experiments, making the study of Taylor bubbles simple and safe. In this chapter, Taylor bubbles are used to study mass transfer with chemical reaction in dependency of various fluid dynamic conditions. Experimental setups are presented to study chemical reactions at Taylor bubbles and in Taylor flows. Furthermore, a Taylor bubble benchmark experiment is presented and used for the validation of numerical simulations that are performed with a front tracking technique in a FEM framework to enable a high resolution of interfaces and boundary layers. It is shown that the interplay of mass transfer, hydrodynamics and chemical reactions can be successfully determined using experimental and numerical methods presented. It is shown further how the selectivity of competitive-consecutive reactions can be influenced by the local fluid dynamics, especially in the wake of a Taylor bubble or within the liquid slug in a Taylor flow.

Low temperature stopped-flow techniques were used to investigate the reaction of three different iron(II) complexes with nitrogen monoxide. The kinetic studies allowed calculation of the activation parameters from the corresponding Eyring plots for all three systems. The reaction of iron(II) chloride with NO leading to the formation of MNIC (mononitrosyl-iron-complex) and DNIC (dinitrosyl-iron-complex) led to activation parameters of ΔH‡ = 55.4 ± 0.4 kJ mol−1 and ΔS‡ = 13 ± 2 J K−1 mol−1 for MNIC and ΔH‡ = 32 ± 6 kJ mol−1 and ΔS‡ = −193 ± 21 J K−1 mol−1 for DNIC. Formation of MNIC turned out to be much faster in comparison with DNIC. In contrast, activation parameters for the formation of monoculear [Fe(bztpen)(NO)](OTf)2 (bztpen = N-benzyl-N,N′,N′-tris(2-pyridylmethyl)-ethylenediamine) ΔH‡ = 17.8 ± 0.8 kJ mol−1 and ΔS‡ = −181 ± 3 J K−1 mol−1 supported an associative mechanism. Interestingly, [Fe(bztpen)(CH3CN)](OTf)2 does not react with dioxygen at all. Furthermore, activation parameters of ΔH‡ = 37.7 ± 0.7 kJ mol−1 and ΔS‡ = −66 ± 3 J K−1 mol−1 were obtained for the reaction of NO with the dinuclear iron(II) H-HPTB complex (H-HPTB = N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane), [Fe2(H-HPTB)(Cl)3]. The kinetic data allowed postulation of the mechanisms for all of these reactions.

The hyponitrite anion is a tentative intermediate in the reduction of nitric oxide (NO) to nitrous oxide (N2O) catalyzed by nitric-oxide reductase (NOR) in the process of bacterial denitrification. Owing to the considerable number of known coordination modes for the hyponitrito ligand, its actual bonding form in the enzymatic cycle is a point of current discussion. Here, we contribute to the hardly known ligand properties of a key intermediate, the monoprotonated hyponitrite anion. Three air- and water-stable ruthenium complexes with hydrogenhyponitrite as the ligand were synthesized by using commercially available bisphosphane co-ligands (1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)ethene (dppv)). The starting compounds [Ru(dppe)(2) (tos))BF4 (1) and [Ru(dpPP)(2) (tos)]BF4 (2) contained the bidentate coordinating tosylate anion (tos) as a particularly well-suited leaving group. To confirm the protonated and deprotonated species, X-ray diffraction, IR, UVNis spectroscopy (solution and solid state), solid-state NMR spectroscopy, and high-resolution mass spectroscopy were used. DFT calculations give insight into the bonding situation. We report on [Ru(dppe)(2) (HN2O2)]BF4 (5), [Ru(dppp)(2) (HN2O2)]BF4 (6), [Ru(dppv)(2) (HN2O2)]BF4 (7), [Ru(dppp)(2) (HN2O2)]BF4 center dot Imi (9;Imi= imidazole) as the first mononuclear trans-hydrogenhyponitrite complexes. Isolated deprotonated analogs are [Ru(dPPe)(2) (N2O2)]center dot Himi(BF4(BF4) (8) and [Ru(dppv)(2) (N2O2)]center dot Himi(BF4)center dot Imi (10).

The colourless solid NO(HSO4), known as "lead-chamber crystals", was investigated ever since its first preparation more than two centuries ago. Its overall ionic nature now is confirmed by X-ray crystallography [Pna2(1), a = 7.3558(4), b = 6.8924(3), c = 7.7017(3) angstrom, Z = 4]. The next neighbours of the NO+ cations are four hydrogensulfate oxygen atoms, forming a distorted square at a distance of about 2.5 angstrom from the nitrogen atom. The square pattern next to the nitrogen atom is the most widespread coordination figure about an NO+ ion in a nitrosyl salt. Depending on the anion, the interaction goes along with a decrease of the N-O stretch's excitation energy.

The design of reactors with a dispersed gas in a liquid phase, e.g., bubble columns, is often based on rather roughly estimated parameters. To obtain a better understanding of the influence and interaction of the fluid dynamics and the mass transfer in the presence of a chemical reaction of NO and Fe(EDTA) in the liquid phase, the complex system of a bubbly flow is here reduced to single-bubble investigations. For this purpose, mass transfer is investigated with and without chemical reaction to be able to differentiate between various influencing factors and determined enhancement caused by the chemical reaction. Two experimental setups are applied, namely, the first one with two moving cameras where the velocity is adapted to the rising velocity of the bubble, and the second one is a counter-current-flow cell.

High-spin nitrosyl-iron centres of the Enemark-Feltham {FeNO}(7) type exist in aqueous solution. Examples include the tentative brown-ring species [Fe(H2O)(5)(NO)](2+) and a tentative Fe-II/edta/NO species formed in the processes for scrubbing NO from flue-gas streams. Inert-gas bubbling through the solutions subdivides the ferrous nitrosyl complexes in a less stable subclass - a prominent member being the brown-ring complex - and a more stable subclass to which the edta species belongs. The structural chemistry of the less stable subclass of {FeNO}(7)-type complexes from aqueous media is presented here. They contain aminecarboxylato co-ligands of limited denticity and aqua ligands that complete an OC-6 environment of the Fe atom. Crystalline compounds for single-crystal structure analysis were obtained for various co-ligands: [Fe(H2O)(2)(ida)(NO)] (2a), [Fe(H2O)(heida)(NO)] (2b), [Fe(H2O)(2)(NO)(oda)] (2c), [Fe(H2O)(2)(NO)(phida)]H2O (2d), [Fe(bnida)(H2O)(2)(NO)] (2e), [Fe(brbnida)(H2O)(2)(NO)] (2f) and [Fe(dipic)(H2O)(2)(NO)] (2g) (ida = iminodiacetate, heida = hydroxyethyliminodiacetate, oda = oxodiacetate, phida = N-phenyliminodiacetate, bnida = N-benzyliminodiacetate, brbnida = N-4-bromobenzyliminodiacetate, dipic = dipicolinate). The Fe-NO interaction was studied by DFT and CASSCF methods. Due to mostly covalent Fe-NO bonds, the charge distribution in the less stable subclass is close to Fe-II(NO) with a small Fe-III(NO-) contribution.

Four crystalline nitrosyl-iron compounds of the {FeNO}(7)(S = 3/2) type with aminecarboxylato co-ligands were prepared from aqueous solutions of iron(II) sulfate, an equimolar amount of one of the co-ligands ethylenediamine-N,N'-diacetate (edda), nitrilotriacetate (nta), N,N'-bis(2-hydroxyethyl)ethylenediamine-N,N'-diacetate (bhedda) or ethylenediamine-N,N,N',N'-tetraacetate (edta) and gaseous nitric oxide. The hemihydrate [Fe(edda)(H2O)(NO)]0.5H(2)O (1.0.5H(2)O), a hydrated coordination polymer [{Fe(H2O)(4)}{Fe(NO)(nta)}(2)](n/n)2H(2)O = [Fe(H2O)(4)(2)(2)](n/n)2H(2)O with [Fe(NO)(nta)](-) (2) monoanions, the solvent-free complex [Fe(bhedda)(NO)] (3) and another coordination polymer [Fe(H2O)(2){Fe(NO)(Hedta)}(2)](n/n) = [Fe(H2O)(2)(4)(2)](n/n) with [Fe(Hedta)(NO)](-) (4) monoanions were investigated by crystallography and IR and UV/Vis spectroscopy. Structural peculiarities, such as a tilt of the NO ligand toward the O atom of a neighbouring carboxylato ligand, were analysed by DFT calculations. The stability of the aqueous solutions of the target compounds against inert-gas stripping was related to the low amount of the less stable aqua complex [Fe(H2O)(5)(NO)](2+) in the aqueous equilibria in addition to the intrinsic stability of the species.

Although the "brown-ring" ion, [Fe(H

International audience; Since the seminal characterisation of two photoinduced linkage isomers (PLIs) in crystals of sodium nitroprusside dihydrate Na2[Fe(CN)5(NO)]·2H2O by photocrystallography, this phenomenon has been described in a large variety of molecular mononitrosyl complexes. The two photoinduced metastable isomers consist of a κO, isonitrosyl, binding mode (MS1) and a κ 2 N,O, side-on, binding mode (MS2). We have recently detected by infrared spectroscopy various PLI states in dinitrosyl ruthenium complexes, for which only κN binding modes were characterised by photocrystallography. We provide here experimental evidences for a photoinduced isonitrosyl isomer in the [Ru(PCy3)2(NO)2Cl]BF4 (Cy=cyclohexyl) complex salt, the results being strongly supported by DFT calculations.

A species model for the copper(II)/L-(+)-tartaric acid (LH2, tartH2) aqueous system between pH 1.9 and 12.3 has been established by potentiometric, UV/Vis spectroscopic, solubility and crystallographic studies. Eight species were detected, including the oligonuclear major species Cu8L6H–10 in the neutral region and the mononuclear major species CuL2H–4 in the alkaline region, the latter being associated with Fehling's solution. The octanuclear complex was isolated as its lithium salt Li7[Cu8(L-tartH–2)4(L-tartH–1)2(H2O)6]NO3·19H2O (1). The “Fehling species” CuL2H–4 was crystallized as its sodium, potassium and caesium salts, namely K2Na4[Cu(L-tartH–2)2]·12H2O (2), Na6[Cu(L-tartH–2)2]·9H2O (3), Na6[Cu(L-tartH–2)2]·14H2O (4), and Cs6[Cu(L-tartH–2)2]·8H2O (5). Each of them shows a distorted square-planar environment of copper(II), similar to the related non-chiral cuprate [Cu(rac-tartH–2-κ2O2,O3)2]6– (S. Albrecht, P. Klufers, Z. Anorg. Allg. Chem. 2013, 639, 280–284). By comparing the components of the UV/Vis spectra of Fehling's solution and the solids, we confirmed the identity of the major solution species.

International audience; Photoinduced metastable linkage NO isomers have been known for a long time in mono-nitrosyl ruthenium or iron transition metal complexes [MLxLy(NO)](n) for which appropriate temperature and excitation conditions allow a controlled generation of different metastable states. Dinitrosyl complexes offer attractive possibilities owing to the potential switching of the two nitrosyl ligands, possibly in a selective manner, leading to a complicated and intricated population of metastable states. [Ru(NO)(2)(PCy3)(2)Cl]BF4 belongs to a complete series of bis-phosphane complex salts of general formula [Ru(NO)(2)(PR3)(2)X](BF4) (X = Cl, Br, I). It presents a square pyramidal geometry with both a linear and a bent NO ligand, and an Ru(d(6)) electron configuration. Multiple light-induced reversible metastable NO linkage isomers (PLIs) are detected by a combination of photocrystallographic and infrared (IR) analysis. The IR signature of three PLI states has been clearly identified. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. After irradiation with 405 nm, the orientation of the bent nitrosyl is changed by rotation towards the Cl ligand, opposite to the linear NO. The minor second metastable state (PLI-2) is proposed to result from a side-bonded (similar to MS2 in mono-nitrosyl complexes) state of the linear nitrosyl.