Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

Summary The kinetics of the Os^VIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN) ₆ ^3– ] and first-order dependence in [OsO₄]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH^–] is a combination of two rate constants; one independent of and the other first-order in [OH^–]. These observations are commensurate with a mechanism in which two complexes, [OsO₄(H₂O)G]^– and [OsO₄(OH)G]^2–, are formed either from [OsO₄(H₂O)(OH)]^– or [OsO₄(OH)₂]^2– and the glycol GH, or by [OsO₄(H₂O)₂] and [OsO₄(H₂O)(OH)]^– and the glycolate ion, G^–, which is in equilibrium with the glycol GH through the reaction between GH and OH^–. Hence there is an ambiguity about the true path for the formation of the two Os^VIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH^– ion on the two species of Os^VIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k₁₁) to positive (related to k₂).     

Untersuchungen an Kristallhydraten anorganischer Salze, 8. Mitt. Interpretation der Schwingungsspektren vonM(BF4)2·6H2O fürM=Fe2+, Co2+, Ni2+

The infrared and Raman spectra were recorded in the range 4000–160 cm^–1 forM(BF₄)₂·6 H₂O whereM=Fe²⁺, Co²⁺, Ni²⁺. The spectroscopic data support the X-ray structural data in showing that in the crystal hydrates studied two kinds of hydrogen bonds are present: H₂O...H₂O and OH₂... F₄B^–. The energies and molecular force constants (f _OH and fH₂O) andr _OH for OH₂...F₄B^– were calculated for the three crystal hydrates. It was found that the bond OH₂... F₄B^– is comparatively weak, with mean energy 3.7–3.3 kcal/mol. Two types of water molecule with different structures are existing as the first are participating in H₂O...H–O–H...F₄B^– and the second in BF₄ ^–...H–O–H...F₄B^–.     

An open-shell INDO study of models for the stabilized O− ion in γ-irradiated alkaline ices

Structural models for stabilized O^– in -irradiated alkaline ices are evaluated. INDO calculations on hydrated O^– indicate octahedral coordination and hydrogen bond orientations for the water molecules are preferred. INDO results for hydrated OH^– are compared with crystallographic data for NaOH hydrates: a scaling factor for calculated hydrogen bond lengths is developed and applied to hydrogen bonded O^– models. The hydrated O^– model is closely similar to the hydrated anions in KF · 4H₂O, NaOH · 4H₂O, and NaOH · 7H₂O. A second model is developed, involving H₃O⁺ along with H₂O, in the O^– stabilization shell. Both models are discussed in terms of alkaline ice radiation chemistry.     

Preparation and characterization of some metal(II) complexes of isocinchomeronic acid and X-ray crystal structure ofcis-diaquabis(hydrogen isocinchomeronato)manganese(II)

The reactions between Mn(II), Co(II), Ni(II), and Zn(II) ions with isocinchomeronic acid (H₂-isocin) afforded complexes of the general formula M(H-isocin)₂-2H₂O, whereas Fe(II) gives both red and deep red-brown products of the same formula. Various physical measurements suggest that the complexes of M = Co, Ni, Zn, and Fe (brown) are octahedrally coordinated by two aqua ligands and twotrans-N,O-bidentate H-isocin^– anions with dimeric hydrogen bonding. Those for M = Mn and Fe (red) are the correspondingcis isomers. The structure of the manganese complex as determined by X-ray crystallography exhibitsC ₂ molecular symmetry with Mn-N = 2.279(2), Mn-O(H-isocin)^– = 2.196(2), and Mn-O(aqua) = 2.137(2) Å. Each aqua ligand forms two donor O-H O hydrogen bonds with carboxy groups of different molecules in adjacent chains.     

An ab initio study of the structures and enthalpies of the hydrogen-bonded complexes of the acids H2O,H2S,HCN, and HCl with the anions OH−, SH−, CN−, and Cl−

Ab initio calculations at second-order Møller-Plesset perturbation theory with the 6-31 + G(d,p) basis set have been performed to determine the equilibrium structures and energies of a series of negative-ion hydrogen-bonded complexes with H₂O, H₂S, HCN, and HCl as proton donors and OH^–, SH^–, CN^–, and Cl^– as proton acceptors. The computed stabilization enthalpies of these complexes are in agreement to within the experimental error of 1 kcal mol^–1 with the gas-phase hydrogen bond enthalpies, except for HOHOH^–, in which case the difference is 1.8 kcal mol^–1. The structures of these complexes exhibit linear hydrogen bonds and directed lone pairs of electrons except for complexes with H₂O as the proton donor, in which cases the hydrogen bonds deviate slightly from linearity. All of the complexes have equilibrium structures in which the hydrogen-bonded proton is nonsymmetrically bound, although the symmetric structures of HOHOH^– and ClHCl^– are only slightly less bound than the equilibrium structures. MP2/6-31 + G(d,p) hydrogen bond energies calculated at optimized MP2/B-31 + G(d,p) and at optimized HF/6-31G(d) geometries are similar. Using HF/6-31G(d) frequencies to evaluate zero-point and thermal vibrational energies does not introduce significant error into the computed hydrogen bond enthalpies of these complexes provided that the hydrogen-bonded proton is definitely nonsymmetrically bound at both Hartree-Fock and MP2.     

Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

A very simple synthesis of K3[Re(NO)(CN)5] · 2 H2O directly from [ReO4]−: Existence of two structural isomers in aqueous medium as indicated by13C N.m.r. spectroscopy

Summary Perrhenate(VII) was reductively nitrosylated using an excess of CN^–, OH^– and NH₂OH · HCl, and from the reaction mixture K₃[Re(NO)(CN)₅] · 2H₂O has been isolated. Its aqueous solution behaves as a 31 electrolyte and its¹³C n.m.r. spectrum in D₂O solution suggests that the complex molecule forms two types of isomeric structure arising from the two different modes of intramolecular hydrogen (deuterium) bonding of the two lattice water (D₂O in the bulk solvent) molecules.     

Synthesis,crystal structure and magnetic properties of the first dinuclear copper(II)–iron(II) complex [Cu(L)Fe(CN)5NO] based on nitroprusside

The nitrosyl cyanide [Cu(L)Fe(CN)₅NO] was prepared by the reaction of [Cu(L)]Cl₂ [L = 3, 10-bis(2-hydroxymethyl)-1,3,5,8,10,12-hexaazacyclotetradecane] with Na₂[Fe(CN)₅NO]·2H₂O in aqueous solution. Single-crystal analysis revealed that the title complex is the first structurally characterized dinuclear copper(II)–iron(II) complex based on the nitroprusside. Variable temperature magnetic susceptibility measurements (4.0–180.0 K) show the occurrence of very weak antiferromagnetic interactions between the copper(II) ions with zJ = –0.410 cm^–1.     

Mechanochemical Reaction of 1,10-Phenanthroline with Metallic Iron

Fe(II) complex is isolated from the products of mechanical activation of a mixture of the powdered carbonyl Fe and 1,10-phenanthroline. According to the data of elemental analysis, an electronic absorption spectra, magnetochemical and EPR studies, the isolated compound is [FePhen₃]²⁺ Phen^–OH^– · 3H₂O that contains Phen^– radical-anion.     

Reactions of p-hydroxyphenyl- and p-phenolatothianium compounds

p-Hydroxyphenylthianium perchlorate reacts with OH^– to give bis(p-phenolatothianium) dihydrate, in which the oxygen atoms of the zwitter ions are tied up in an eight-membered ring by hydrogen bonds with the H₂O molecules, The unit cell of the perchlorate consists of two cations and two anions bonded by linear and forked hydrogen bonds. p-Hydroxyphenylthianium perchlorate reacts with a concentrated solution of KOH in methanol to give 1-(p-hydroxyphenyl)-1-(p-phenolato)bisthianium perchlorate, which is also obtained by the reaction of p-hydroxyphenylthianium perchlorate with bis(p-phenolatothianium) dihydrate and of the latter with HClO₄. 1-(p-Hydroxyphenyl)-1'-(p-phenolato)bisthianium chloride hydrate and 1-(p-phenolato)thianiumbisphenol, respectively, were obtained by the reaction of bis (p-phenolatothianium) dihydrate with p-hydroxyphenylthianium chloride or with C₆H₅OH. Under the influence of picric or perchloric acid, 1-(p-h droxyphenyl)-1'-(p-phenolato)bisthianium perchlorate is converted to p-hydroxyphenylthianium picrate or its perchlorate, respectively, while reaction with OH^– gives bis(p-phenolatothianium) dihydrate, and heating with piperidine gives p-hhdroxyphenyl -piperidinoamyl sulfide. When bis(p-phenolatothianium) dihydrate is heated, it undergoes dehydration and polymerization to [-OC₆H₄S(CH₂)₅-]_n; depending on the conditions, n = 2, 3, 14, or 25. p-Hydroxyphenyl -piperidinoamyl sulfide is formed when II is heated with piperidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1050–1055, August, 1980.     

A kinetic and mechanistic study of oxidation of arsenic(III) by hexacyanoferrate(III) in aqueous ethanoic acid

The kinetics of oxidation of As^IIIby Fe(CN)₆ ^3– has been studied spectrophotometrically in 60% AcOH–H₂O containing 4.0moldm^–3HCl. The oxidation is made possible by the difference in redox potentials. The reaction is first order each in [Fe(CN)₆ ^3–] and [As^III]. Amongst the initially added products, Fe(CN)₆ ^4– retards the reaction and As^Vdoes not. Increasing the acid concentration at constant chloride concentration accelerates the reaction. At constant acidity increasing chloride concentration increases the reaction rate, which reaches a maximum and then decreases. H₂Fe(CN)₆ ^–, is the active species of Fe(CN)₆ ^3–, while AsCl₅ ^2– in an ascending portion and AsCl₂ ⁺ in a descending portion are considered to be the active species of As^III. A suitable reaction mechanism is proposed and the reaction constants of the different steps involved have been evaluated.     

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from [FeL(OH)2]− complex, (L=N-(2-hydroxyethyl) iminodiacetate anion

Summary The kinetics and mechanism of the system [FeHIDA-(OH)₂]^–+5CN^–[Fe(CN)₅OH^–+HIDA^2–+OH^– (HIDA=N-(2-hydroxyethyl) (iminodiacetate) at pH=9.5±0.02, I=0.1 M and at 25±0.1°C have been studied spectrophotometrically at 395 nm ( _max of [Fe(CN)₅OH]^3–]. The reaction has three distinguishable stages; the first is formation of [Fe(CN)₅OH]^3–, the second is conversion of [Fe(CN)₅OH]^3– into [Fe(CN)₆]^3–, and last is the reduction of [Fe(CN)₆]^3– to [Fe(CN)₆]^4– by the HIDA^2– released in the first stage. The first stage shows variable-order dependence on cyanide concentration, unity at high cyanide concentration and zero at low cyanide concentration. The second stage exhibits first-order dependence on the concentration of [Fe(CN)₅OH]^3– as well as on cyanide. The reverse reaction between [Fe(CN)₅OH]^3– and HIDA^2– is first-order in each of these species and inverse first-order in cyanide. On the basis of forward and reverse rate studies, a five-step mechanism has been proposed for the first stage. The first step involves a slow loss of one OH^–, by a cyanide-independent path.     

Solvent effects on chemiluminescence from the hydrogen peroxide-lucigenin reaction: Kinetics of light emission in mixed polar solvents

Summary The effect of reaction media composition on reaction kinetics was studied for the reaction of lucigenin (10,10-dimethyl-9,9-biacridinium nitrate) with hydrogen peroxide and alkali. Chemiluminescent emission as well as lucigenin disappearance were recorded in mixtures of water with the co-solvents methanol, ethanol, 1-propanol, dimethylsulfoxide, and dimethylformamide. The kinetic results (base and peroxide concentration influence on the reaction rate and the relative chemiluminescence yield) are very similar in all the reaction media, suggesting that the fundamental step in the disappearance of lucigenin and in light emission decay is HO ₂ ^– addition to lucigenin. Lucigenin can also disappear through dark reactions with OH^– or H₂O₂. The co-solvent acts as a catalyst for the reaction with HO ₂ ^– and increases both the initial chemiluminescence intensity and the decay rate constant.

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Lösungsmitteleffekte bei der Chemilumineszenz der Wasserstoffperoxid-Lucigenin Reaktion. Kinetik der Lichtemission in gemischten polaren Lösungsmitteln

Zusammenfassung Es wurde der Einfluß der Zusammensetzung des Reaktionsmediums auf die Kinetik der Reaktion von Lucigenin (10,10-dimethyl-9,9-biacridiniumnitrat) mit Wasserstoffperoxid und Alkali untersucht. Die Emission der Chemilumineszenz und das Verschwinden von Lucigenin wurde in Mischungen von Wasser mit den Kosolventien Methanol, Ethanol, 1-Propanol, Dimethylsufoxid und Dimethylformamid gemessen. Die kinetischen Resultate (Einfluß der Basen- und Peroxid-Konzentration auf die Reaktionsgeschwindigkeit und die relative Chemilumineszenzausbeute) sind für alle Reaktionsmedien sehr ähnlich; das legt den Schluß nahe, daß der grundlegende Schritt im Verbrauch des Lucigenin unter Lichtemission die Addition von HO ₂ ^– an Lucigenin ist. Lucigenin kann auch über Dunkelreaktionen mit OH^– oder H₂O₂ verschwinden. Das Kosolvens agiert als Katalysator für die Rekation mit HO ₂ ^– und erhöht sowohl die anfängliche Chemilumineszenzintensität als auch die Zerfallsgeschwindigkeitskonstante.

     

Reaction of nitrogen oxides with salts of metal-substituted heteropolyanions

We have used IR spectroscopy to study the reaction with NO and NO₂ of solid tetramethylammonium and cesium salts of heteropolyanions (HPA) PW₁₁M(L) _0.39 ^n– [M=V(V), Cr(III), Mn(II), Fe(II, III), Co(II), Ni(II), Cu(II); L=H₂O, OH^– or O^2–], preevacuated at 110°C or 300°C. Only in the case of Fe(II)-substituted heteropolyanions are nitrosyl complexes formed: PW₁₁Fe(NO)O ₃₉ ^5– (vNO=1730 cm^–1), which leads to stabilization of the NO molecules with respect to oxidation by oxygen. We observed reversible reaction with NO₂ by the listed heteropoly complexes. The vibrational frequencies of adsorbed NO₂ are virtually independent of the metal M and its coordination environment in the heteropolyanion (v₁=1335–1360) and v₃=1620–1640 cm^–1). This provides a basis for assuming that the NO₂ groups are bonded to the oxygen atoms in the heteropoly anion with formation of the fragments O_HPA...NO₂.Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1966–1971, September, 1992.     

Synthesis of di-Iron-Containing Inorganic Synzyme, γ-SiW10{Fe(OH2)}2O386?, and the Liquid-Phase Oxidation Catalysis

The Keggin-type di-iron-substituted silicotungstate, -SiW₁₀{Fe(OH₂)}₂O₃₈ ^6– (I), was synthesized by the reaction of the lacunary [-SiW₁₀O₃₆]^8– with Fe(NO₃)₃ in an acidic aqueous solution and isolated as the tetra-n-butylammonium salt (TBA-I). It was characterized by various analyses and the structure with the oxo-bridged di-iron site was clarified. TBA-I was stable and catalyzed selective oxidation of various alkanes and alkenes with hydrogen peroxide: cyclohexane, adamantane, n-hexane, and n-pentane were catalytically oxidized. Even lower alkanes such as methane, ethane, propane, and n-butane were catalytically oxidized. It was remarkable that the efficiency of hydrogen peroxide utilization to oxygenated products reached up to ca. 100% for the oxidation of cyclohexane and adamantane. Alkenes were mainly epoxidized with hydrogen peroxide. It was demonstrated that the TBA-I showed high turnover number of 135–147 for the oxidation of cyclohexane with 1 atm oxygen.     

Effect of ionic strength and ionic interactions on the oxidation of Fe(II)

The rates of oxidation of Fe(II) in NaCl and NaClO ₄ solutions were studied as a function of pH (6 to 9), temperature (5 to 25°C), and ionic strength (0 to 6m). The rates are second order with respect to [H⁺] or [OH^–] and independent of ionic strength and temperature. The overall rate of the oxidation is given by

Kinetics and mechanism of metal ion catalysis. Part III. Osmium(VIII) catalysed oxidation of m-hydroxybenzaldehyde by Fe(CN)6 3− in alkaline medium

Os^VIII-catalysed oxidation of m-hydroxybenzaldehyde by alkaline Fe(CN)₆ ^3– has been studied in the 0.01–0.05 M [OH^–] range. Higher [OH^–] concentrations were not possible as the substrate turned yellow at [OH^–] > 0.05 M. The very low solubility of the substrate in H₂O restricted the kinetic study to [OH^–] < 0.01 M. A mechanism, consistent with the results is proposed.     

An independent kinetic and mechanistic study of the secondary reactions in the substitution of [FeL(OH)](n−2)− (L= triethylenetetraaminehexaacetic acid) by cyanide ions

Summary The kinetics of reaction between [Fe(CN)₅OH]^3– and CN^– have been investigated spectrophotometrically at pH=11.00, I=0.25 M(NaClO₄) and temp.=25.0°C by disappearance of the absorption peak at 395 nm. The rate data for this reaction followed first order kinetics in both [Fe(CN)₅OH^3–] and [CN^–]. The second order rate constant (k_f) was found to be (3.44±0.08)×10^–3 M^–1 s^–1. The pH dependence of the reaction was also investigated in the range 9–12. The activation parameters were found to be H=36.4kJ mol^–1 and S=–168JK^–1 mol^–1.The reaction between [Fe(CN)₆]^3– and TTHA^6– (TTHA=triethylenetetraaminehexaacetic acid) has also been followed spectrophotometrically at 420 nm, pH=11.00, I=0.1M (NaClO₄) and temp.=25.0°C. This reaction also followed first order kinetics in both [Fe(CN) ₆ ^3– ] and [TTHA^6–]. The second order rate constant (k_f) was found to be (3.74±0.21)×10^–2 M^–1 s^–1. The rate of reaction was found to increase with pH in the range 9–11.5. The different reactive species of TTHA (L) are H₂L^4– HL^5– and L^6–. The rate constants for these species have been calculated and the pH profile is explained. The values of the activation parameters were found to be H= 30.9 kJmol^–1 and S=–167JK^–1 mol^–1. Electron transfer from [Fe(CN)₆]^3– to the substrate followed by decomposition of the latter is proposed. The oxidation products of TTHA have been investigated by g.l.c.     

Raman Spectroscopy of Aqueous ZnSO4 Solutions under Hydrothermal Conditions: Solubility, Hydrolysis, and Sulfate Ion Pairing

Raman spectra have been measured for aqueous ZnSO₄ solutions under hydrothermal conditions at steam saturation to 244°C; solubility has been recorded as a function of temperature from 25 to 256°C. The high-temperature Raman spectra contained two polarized bands, which suggest that a second sulfato complex, possibly bidentate, is formed in solution, in addition to the 1:1 zinc(II) sulfato complex, which is the only ion pair identified at lower temperatures. Under hydrothermal conditions, it was possible to observe the hydrolysis of the zinc(II) aquo ion by measuring the relative intensity of bands due to SO ₄ ^2– and HSO ₄ ^– according to the equilibrium reaction Zn(OH₂)₆]²⁺ + SO ₄ ^2– [Zn(OH₂)₅OH]⁺ + HSO ₄ ^– The precipitate in equilibrium with the solution at 210°C could be characterized as ZnSO₄ · H₂O (gunningite) by x-ray diffraction (XRD) and Raman and infrared spectroscopy. At 244°C the equilibrium precipitate could be identified as ZnSO₄ (zincosite).     

Porphyrins

The extended Hückel model is further developed to allow prediction of spin state and is applied to ferrous porphin complexes with H₂O, CO, O₂, N₂ and ferric porphin complexes with OH^–, F^–, Cl^–, CN^–. The model shows that if the iron atom lies in the porphyrin plane only low or intermediate spin states are possible, with the weakest ligands just producing low spin. The high spin (ionic) complex can only occur with iron displaced from the plane, in which geometry CO and CN^– are calculated to be low spin, OH^–, F^–, Cl^– high spin, and H₂O borderline between low and high. The model predicts that N₂ will not bond and that a stable O₂ complex is impossible if O₂ is perpendicular to the plane. Discussion is given of the ligand field, absorption spectra, soft X-ray spectra, and Mössbauer spectra.

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Zusammenfassung Das erweiterte Hückelmodell wird in einer Weise ausgebaut, daß Aussagen über Spinzustände möglich werden. Das Verfahren wird auf eisen-(II)-haltige Porphyrinkomplexe mit H₂O, CO, O₂ und N₂ als Liganden und eisen-(III)-haltige Komplexe mit OH^–, F^–, Cl^– und CN^– angewendet. Dabei zeigt sich, daß nur Zustände mit niedrigem oder mittlerem Spin möglich sind, wenn das Eisenatom in der Porphyrin-Ebene liegt, und daß dabei die schwächsten Liganden den niedrigsten Spin ergeben. Komplexe mit hohem Spin (Ionenkomplexe) sind nur dann möglich, wenn das Eisen nicht in der Ebene liegt, und zwar haben dann der CO- und der CN^–-Komplex niedrigen, der OH^–-, F^–- und Cl^–-Komplex hohen und der H₂O-Komplex entweder hohen oder niedrigen Spin. Das Modell ergibt ferner, daß N₂ nicht gebunden wird und daß ein stabiler O₂-Komplex nur entsteht, wenn das O₂-Molekül senkrecht zur Bindungsebene steht. Zum Schluß werden Ligandenfeld, Absorptionsspektren, weiche Röntgenspektren und Mössbauerspektren diskutiert.

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Résumé Le modèle de Hückel étendu est élaboré de manière á permettre la prédiction de l'état de spin et est appliqué aux complexes de la porphine ferreuse avec H₂O, CO, O₂, N₂ et de la porphine ferrique avec OH^–, F^–, Cl^–, CN^–. Ce modèle montre que, si l'atome de fer se trouve dans le plan de la porphyrine, seuls des états de spin bas et intermédiaires sont possibles, les ligands les plus faibles donnant seulement un spin bas. Le complexe à spin élevé (ionique) ne peut exister qu'avec le fer en dehors du plan, auquel cas on calcule un spin bas pour CO et CN^–, haut pour OH^–, F^–, Cl^–, et l'un ou l'autre pour H₂O. Ce modèle permet de prédire que N₂ ne se liera pas et qu'un complexe stable avec O₂ est impossible si O₂ est perpendiculaire au plan. On discute le champ des ligands, le spectre d'absorption, le spectre des rayons X mous et le spectre Mössbauer.

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National Institutes of Health Pre-Doctoral Fellow.