Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from mono(aminocarboxylato)iron(III) complexes

Summary The kinetics and mechanism of the system: [FeL(OH)]^2–n + 5 CN^– [Fe(CN)₅(OH)]^3– + L^n–, where L=DTPA or HEDTA, have been investigated at pH= 10.5±0.2, I=0.25 M and t=25±0.1 C.As in the reaction of [FeEDTA(OH)]^2–, the formation of [Fe(CN)₅(OH)]^3– through the formation of mixed ligand complex intermediates of the type [FeL(OH)(CN)_x]^2–n–x, is proposed. The reactions were found to consist of three observable stages. The first involves the formation of [Fe(CN)₅(OH)]^3–, the second is the conversion of [Fe(CN)₅(OH)]^3– into [Fe(CN)₆]^3– and the third is the reduction of [Fe(CN)₆]^3– to [Fe(CN)₆]^4– by oxidation of L^n– The first reaction exhibits a variable order dependence on the concentration of cyanide, ranging from one at high cyanide concentration to three at low concentration. The transition between [FeL(OH)]^2–n and [Fe(CN)₅(OH)]^3– is kinetically controlled by the presence of four cyanide ions around the central iron atom in the rate determining step. The second reaction shows first order dependence on the concentration of [Fe(CN)₅(OH)]^3– as well as on cyanide, while the third reaction follows overall second order kinetics; first order each in [Fe(CN)₆]^3– and L^n–, released in the reaction. The reaction rate is highly dependent on hydroxide ion concentration.The reverse reaction between [Fe(CN)₅(OH)]^3– and L^n– showed an inverse first order dependence on cyanide concentration along with first order dependence each on [Fe(CN)_5– (OH)]^3– and L^n–. A five step mechanism is proposed for the first stage of the above two systems.     

A theoretical study of the relative stability of the isomeric forms of N2O3

The electronic structure, geometrical parameters and relative stability of the isomeric forms of N₂O₃ are analysed by means of ab initio calculations. Total energies of the different isomers are given. The energy difference between the most stable conformers of the symmetric N₂O₃ is 4.31 Kcal mol^–1 as provided by 6–31G basis set. The height of the rotational barrier determined by the ab initio technique is 7.12 kcal mol^–1.Member of the Carrera del Investigador CICPBA, R. Argentina.Member of the Carrera del Investigador CONICET, R. Argentina.Predoctoral fellow of CONICET, R. Argentina.     

Synthesis,protonation and substitution behaviour of K3[ReO2(CN)4]

Summary The preparation and characterization of salts of the [ReO₂(CN)₄]^3–, [ReO(OH)(CN)₄]^2–, [ReO(H₂O)(CN)₄]^–, [Re₂O₃(CN)₈]^4– and [ReO(NCS)(CN)₄]^2– species are described. The nature of the protonation reactions of [ReO₂(CN)₄]^3– was established by the successful isolation of these salts.     

Syntheses,crystal structures and magnetic properties of two honeycomb-layered bimetallic assemblies,K2[NiII(cyclam)]3[FeII(CN)6]2 · 12H2O and [NiII(cyclam)]3[FeIII(CN)6]2 · 16H2O

Two bimetallic assemblies, K₂[Ni^II(cyclam)]₃[Fe^II(CN)₆]₂ · 12H₂O (1) and [Ni^II(cyclam)]₃[Fe^III(CN)₆]₂ · 16H₂O (2) (cyclam = 1,4,8,11-tetraazacyclotetradecane), were obtained by reaction of K₄[Fe(CN)₆] and [Ni(cyclam)](ClO₄)₂ in aqueous media at different temperatures. Their crystals were structurally determined and magnetic properties were studied. Both of the compounds have honeycomb-layered structures, which are formed by Fe₆Ni₆ units linked through the cyanide bridges. Structure (1) consists of polyanions containing Ni^II–NC–Fe^II linkages and K⁺ cations, while structure (2) is a two-dimensional neutral layer containing Ni^II–NC–Fe^III linkages. The magnetic properties of (1) and (2) have been investigated in the 5–300 K range. Compound (1) exhibits a weak antiferromagnetic interaction with Weiss constant = –0.35 K; compound (2) shows ferromagnetic intralayer and antiferromagnetic interlayer interactions.     

Oxopentacyano-complexes of molybdenum(IV) and tungsten(IV) in photolysis of octacyanometalates(IV)

Summary Ligand-field (LF) photolysis of aqueous alkaline solutions of K₄[M(CN)₈] (M = Mo or W) containing KCN produces [MO(CN)₅]^3– species. NaCs₂]MO(CN)₅] was isolated and characterised by u.v.-vis., i.r. and Raman spectroscopy. In addition, the reactions of [MO(OH)(CN)₄]^3– with free CN^– are described and the relations between octa-, penta- and tetra-cyanocomplexes are summarised.     

Dinuclear complexes with a μ-cyano ligand. Part XI(1). Synthesis and characterization of several derivatives ofcis-[Co(NH3)(en)2(H2O)]3+

Summary The new complex double saltscw-[Co(NH₃)(en)₂(H₂O)]₂ [M(CN)₄]₃ (en = ethylenediamine; M = Ni, Pd or Pt),cis-[Co(NH₃(en)₂(H₂O)]₂[FeNO(CN)₅]₃ andcis-[Co(NH₃)(en)₂(H₂O)][Co(CN)₆] have been synthesized and by anation in the solid state the corresponding new dinuclear complexes with a cyano bridgecis- ortrans-[(NH₃)(en)₂Co-NC-M(CN)₃]₂ [M(CN)₄] (M = Ni, Pd or Pt);cis-, trans-[(NH₃)(en)₂Co-NC-FeNO(CN)₄]₂[FeNO(CN)₅] andcis-[(NH₃)(en)₂Co-NC-Co(CN)₅ have been prepared. The complexes have been characterized by chemical analysis, t.g. measurements, and by i.r. and electronic spectroscopy. With [Ni(CN)₄][^2– and [Co(CN)in]₆ ^3– only thecis-isomer is produced; with [Pd(CN)₄]^2–, [Pt(CN)₄]^2– and [FeNO(CN)₅]^2– thetrans- isomer is the dominant species. The dinuclear complex derived from [Pt(CN)₄]^2– shows strong Pt-Pt interactions both in the solid state and in solution.     

Syntheses,crystal structures and magnetic properties of two cyano-bridged two-dimensional assemblies [Fe(salpn)]2 [Fe(CN)5NO] and [Fe(salpn)]2[Ni(CN)4]

Two cyano-bridged assemblies, [Fe^III(salpn)]₂[Fe^II(CN)₅NO] (1) and [Fe^III (salpn)]₂[Ni^II(CN)₄] (2) [salpn = N, N-1,2-propylenebis(salicylideneiminato)dianion], have been prepared and structurally and magnetically characterized. In each complex, [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– coordinates with four [Fe(salpn)]⁺ cations using four co-planar CN^– ligands, whereas each [Fe(salpn)]⁺ links two [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– ions in the trans form, which results in a two-dimensional (2D) network consisting of pillow-like octanuclear [—M^II—CN—Fe^III—NC—]₄ units (M = Fe or Ni). In complex (1), the NO group of [Fe(CN)₅NO]^2– remains monodentate and the bond angle of Fe^II—N—O is 180.0°. The variable temperature magnetic susceptibilities, measured in the 5–300 K range, show weak intralayer antiferromagnetic interactions in both complexes with the intramolecular iron(III)iron(III) exchange integrals of –0.017 cm^–1 for (1) and –0.020 cm^–1 for (2), respectively.     

New Layered Polymer [{Mn(H2O)3}2{Re6Se8(CN)6}] · 3.3H2O: Synthesis and Properties

The [{Mn(H₂O)₃}₂{Re₆Se₈(CN)₆}] · 3.3H₂O complex was produced on slow evaporation of an aqueous solution containing the salt of a cluster complex K₄Re₆Se₈(CN)₆ · 3.5H₂O and a 23-fold excess of Mn²⁺. The cluster complexes [Re₆Se₈(CN)₆]^4– are linked in a crystal into the charged coordination layers [{Mn(H₂O)₃}₄{Re₆Se₈(CN)₆}₃]^4– ₂ through the Mn²⁺ cations. The Mn²⁺ cations are coordinated in a layer by three cyano nitrogen atoms of the cluster complexes; the Mn–N bond lengths are 2.13(4) and 2.21(2) Å. Each [Re₆Se₈(CN)₆]^4– anion is bonded to three manganese cations Mn(1). The anions are bonded additionally to the Mn(2) cations disordered over two close positions.     

Structures of hexanuclear molybdenum chalcocyanide complexes: electronic absorption spectra and DFT calculation

Electronic absorption spectra of aqueous solutions of the clusters K₆[Mo₆Q₈(CN)₆] and K₇[Mo₆Q₈(CN)₆] (Q = S, Se) were studied. The electronic structures of the [Mo₆Q₈(CN)₆]^6– and [Mo₆Q₈(CN)₆]^7– cluster anions were calculated by the DFT method. The absorption spectra observed agree with the results of calculation in the framework of the electron-dipole transition model.     

Solvent dependence of charge-transfer transitions in binary aqueous mixtures as an indicator of preferential solvation

Summary Wavelengths of maximum absorptions are reported for the main metal-to-ligand charge transfer-bands (MLCT) of complexes [Fe(CN)₅(4-phpy)]^3– and [Fe(CN)₅(4-t-bupy)]^3– (4-phpy=4-phenylpyridine and 4-t-bupy=4-t-butylpyridine) in several series of mixed solvents. Correlations of the shifts in MLCT energies as a function of dielectric constant and polarizability of the medium have been investigated. The interpretation of the medium effects on E_op (MLCT) takes into account the process of preferential solvation of solutes by solvent molecules.     

Thermal and photochemical interaction of octacyanometallates(IV), [M(CN)8]4− (M = Mo or W) in the presence of pyrazine

The interactions between [M(CN)₈]^4– (M = Mo or W) and pyrazine (pz) in the solid state and in aqueous solutions have been analysed. In strongly acidic solutions {pzH⁺, [M(CN)₈]^4–} ion pair formation is observed; the pyrazinium salts (pzH)₂(H₃O)₂[Mo(CN)₈]·0.5pz·3H₂O and (pzH)₂K(H₃O)[W(CN)₈]·H₂O have been isolated. The X-ray crystal structure of the latter, and the spectroscopic properties of both, are described. The [W(CN)₈]^4– anion is approximately square antiprismatic (D_4d), with different H-bond environments around the N atoms. The ligand-field photolysis of [M(CN)₈]^4– in the presence of pyrazine in neutral and alkaline solution results in the formation of tetracyanooxometallates(IV) in equilibrium with pentacyanooxometallates(IV) through the [M(CN)₇(pz)]^3– anions as intermediates. The formation of the [M(CN)₆(pz)₂]^2– ion, postulated in the literature to be the final product of the alkaline photolysis, has definitively been excluded.     

Kinetic and mechanism of pentacyanohydroxoferrate(III) formation from the reaction of [Fe2HPDTA(OH)2] with cyanide ions

Summary The kinetics and mechanism of exchange of HPDTA in [Fe₂HPDTA(OH)₂] with cyanide ion (HPDTA=2-hydroxytrimethylenediaminetetraacetic acid) was investigated spectrophotometrically by monitoring the peak at 395 nm ( _max of [Fe(CN)₅OH]^3– at pH=11.0±0.02,I=0.25m (NaClO₄) at ±0.1°C).Three distinct observable stages were identified; the first is the formation of [Fe(CN)₅OH]^3–, the second the formation of [Fe(CN)₆]^3– from it and the third the reduction of [Fe(CN)₆]^3– to [Fe(CN)₆]^4– by HPDTA^4– released in the first stage.The first stage follows first-order kinetics in [Fe₂HPDTA(OH)₂] and second-order in [CN^–] over a wide range of [CN^–], but becomes zero order at [CN^–]<5×10^–2 m. We suggest a cyanide-independent dissociation of [Fe₂HPDTA)(OH)₂] into [FeHPDTA(OH)] and [Fe(OH)]²⁺ at low cyanide concentrations and a cyanide-assisted rapid dissociation of [Fe₂HPDTA(OH)₂] to [FeHPDTA(OH)(CN)]^3– and [Fe(OH)]²⁺ at higher cyanide concentrations. The excess of cyanide reacts further with [FeHPDTA(OH)(CN)]^3– finally to form [Fe(CN)₅OH]^3–.The reverse reaction between [Fe(CN)₅OH]^3– and HPDTA^4– is first-order in [Fe(CN)₅OH]^3– and HPDTA^4–, and exhibits inverse first-order dependence on cyanide concentration.A six-step mechanism is proposed for the first stage of reaction, with the fifth step as rate determining.     

Hexamethylphosphorsäuretriamid als Ligand, 3. Mitt.: Umsetzungen von [Co(HMPT)4]2+ mit Rhodanid-, Cyanid- und Azidionen

Zusammenfassung Auf Grund spektrophotometrischer, potentiometrischer und konduktometrischer Befunde entstehen aus [Co(HMPT)₄]²⁺ in Hexamethylphosphorsäuretriamid (HMPT) bei Zusatz von Pseudohalogenidionen folgende Koordinationsformen: [Co(HMPT)₃N₃]⁺, [Co(HMPT)₂(N₃)₂], [Co(HMPT)(N₃)₃]^–, [Co(N₃)₄]^2–, [Co(HMPT)₃NCS]⁺, [Co(HMPT)₂(NCS)₂], [Co(HMPT)(NCS)₃]^–, [Co(NCS)₄]^2–, [Co(HMPT)₂(CN)₂], [Co(HMPT)(CN)₃]^–, [Co(HMPT)(CN)₅]^3–.

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Hexamethyl phosphoric triamide as a ligand, III: Reactions of [Co(HMPT)₄]²⁺ with rhodanide, cyanide, and azide ions, resp

Spectrophotometric, potentiometric and conductometric results indicate that addition of pseudohalide ions to [Co(HMPT)₄]²⁺ in hexamethylphosphoramide (HMPT) leads to the following coordination forms: [Co(HMPT)₃N₃]⁺, [Co(HMPT)₂(N₃)₂], [Co(HMPT)(N₃)₃]^–, [Co(N₃)₄]^2–, [Co(HMPT)₃NCS]⁺, [Co(HMPT)₂(NCS)₂], [Co(HMPT)(NCS)₃]^–, [Co(NCS)₄]^2–, [Co(HMPT)₂(CN)₂], [Co(HMPT)(CN)₃]^–, [Co(HMPT)(CN)₅]^3–.

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Mit 7 Abbildungen

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2. Mitt.:V. Gutmann undA. Weisz, Mh. Chem.100, 2104 (1969).     

Low-temperature DTA- and IR-studies on barium nitroprusside trihydrate,Ba[Fe(CN)5NO]·3H2O

The results of a DTA study between room temperature and 90 K on barium nitroprusside trihydrate, (BaNP), Ba[Fe(CN)₅NO]·3H₂O, complemented by temperature-scanning IR transmission spectroscopy are reported.

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Zusammenfassung Ergebnisse einer DTA-Untersuchung von Bariumnitroprussidtrihydrat Ba[Fe(CN)₅NO]3H₂O (BaNP) im Temperaturintervall Zimmertemperatur bis 90 K, ergänzt durch Temperatur-Scanning IR Transmissionsspektroskopie werden beschrieben.

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Dedicated to Prof. Dr. H. J. Seifert on the occasion of his 60^th birthday

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Research Fellow of CONICET, Argentina

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Holder of scholarship granted by CONICET, Argentina

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This work was supported by CONICET, Argentina, through grants PIDs 3-070600/88, 3-906704/85 and 3076100/88, and by CONICOR, Córdoba-Argentina, through grant 1725/90. The Alexander von Humboldt Foundation, F. R. Germany, kindly provided some pieces of equipment.     

Photochemical reactions of molybdenum and tungsten octacyanometallates(IV) in acidic aqueous media containing 2,2′-bipyridyl or 1,10-phenanthroline

Summary The reaction scheme of acidic photolysis of [M(CN)₈]^4– (M = Mo or W) in the presence of 2,2-bipyridyl (bipy) or 1,10-phenanthroline (phen) based on previous reports, and the present results, is given. In this scheme the formation of [M(CN)₆(N-N)]^2– (M = Mo or W), postulated in the literature to be a main product of photoexcitation of [M(CN)₈]^4– in the presence of bipy or phen, has definitively been excluded. The main cyano-polypyridyl species formed are [MO(CN)₃(N-N)]^– ions which, in acidic solution, undergo further reactions. A new product, [MoO(CN)₂(N-N)₂], resulting from thermal replacement of the cyanide ligand by polypyridyl, has been detected.Author to whom all correspondence should be directed.     

cis- und trans-Disulfitotetracyanokobaltate(III)

The preparation and the properties of a series of salts containing the new anion cis-[Co(SO₃)₂(CN)₄]^5? are described. The method of preparation of the trans[Co(SO₃)₂ · (CN)₄^5? complex is improved and the new salt K₄[CoSO₃(CN)₅] · 4H₂O is described. The configuration of the cis- and trans-[Co(SO₃)₂(CN)₄]^5? complexes results from their Raman, IR and UV spectra.     

A novel three-dimensional mixed bridging–ligand complex with an unexpected 1,3-diaminopropane bridge

Reaction of K₃[Fe(CN)₆] with [Cu(tn)₂](ClO₄)₂ (tn=1,3-diaminopropane) leads to a novel mixed cyano and tn bridged three-dimensional (3D) bimetallic assembly (1), in which each [Fe(CN)₆]⁴⁻ anion connects six copper(II) cations via six CN⁻ groups, whereas each copper(II) cation is linked to three [Fe(CN)₆]⁴⁻ ions and two other copper(II) ions through Cu–NC–Fe and Cu–tn–Cu linkages, respectively. Magnetic studies reveal weak antiferromagnetic interactions between the nearest Cu^II (S=1/2) ions through the diamagnetic [Fe(CN)₆]⁴⁻ anion.     

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from the reaction of cyanide ion with [Fe2L(OH)2]2− (L=triethylenetetraaminehexaacetate)

Summary The kinetics and mechanism of the reaction between [Fe₂L(OH)₂]^2– and cyanide ion (L = TTHA, triethylenetetraaminehexaacetate) have been studied spectrophotometrically atpH=11.0±0.1,I=0.1 M(NaClO₄) and T = 25±0.1 °C. The overall reaction consists of three distinct, observable stages. The first stage involves the dissociation of the binuclear complex into a mononuclear complex [FeL(OH)]^4– which then reacts with cyanide to form [Fe(CN)₅OH]^3–. The species [Fe(CN)₅OH]^3– reacts further with an excess of cyanide and forms [Fe(CN)₆]^3– in the second stage of reaction. The last stage involves the reduction of [Fe(CN)₆]^3– formed in the second stage by the TTHA^6– released in the first stage of reaction. The formation of [Fe(CN)₅OH]^3– in the first stage is firstorder in [Fe₂L(OH)₂]^2– and third-order in cyanide over a large range of cyanide concentrations but becomes zero-order in cyanide at [CN^–] < 4×10^–2M.These observations enable us to suggest the presence of a slow step in which [Fe₂L(OH)₂]^2– dissociates into [FeL(OH)]^4– and [FeOH]²⁺ at low cyanide concentrations and a cyanide assisted rapid dissociation of [Fe₂L(OH)₂]^2– to [FeL(OH)(CN)]^5– at higher cyanide concentrations. The species [FeL(OH)(CN)]^5– reacts further with an excess of cyanide to produce [Fe(CN)₅OH]^3– finally.The reverse reaction between [Fe(CN)₅OH]^3– and TTHA^6– follows first-order dependence in each of [Fe(CN)₅OH]^3– and TTHA^6– and inverse first-order dependence on cyanide concentration. A six-step mechanism has been proposed for the first stage of reaction in which the fifth has been identified as the rate-determining step.     

Mechanisms of oxidation of K4Fe(CN)6 by hypochlorous acid and catalytic activation by azide, bromide, and iodide

Summary HOCl reacts with Fe(CN) ₆ ^4– to generate an intermediate, presumably FeCl(CN) ₆ ^3– , which exhibits a weak absorption around 282 nm and decays simultaneously with the formation of Fe(CN) ₆ ^3– . When decreasing the HOCl/Fe(CN) ₆ ^4– concentration ratio fromR>1 toR<1, a drastic change in the kinetics of the oxidation is observed. Depending onR, the intermediate obviously oxidizes either Fe(CN) ₆ ^4– or HOCl. AtR1, a further intermediate appears which also precedes the oxidation and absorbs strongly around 360 nm. The intermediates detected may represent reactive high oxidation states of iron (Fe(IV) and Fe(VI)). HOCl induced oxidation of Fe(CN) ₆ ^4– is activated catalytically by Br^–, I^–, and N ₃ ^– , obviously due to generation of stronger oxidants (HOBr, HOI, and ClN₃), but oxidation is efficiently inhibited by CN^– and NCS^–.

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Mechanismen der Oxidation von K₄Fe(CN)₆ durch Hypochlorsäure und katalytische Aktivierung durch Azid, Bromid und Iodid

Zusammenfassung HOCl reagiert mit Fe(CN) ₆ ^4– unter Bildung eines Intermediats, vermutlich FeCl(CN) ₆ ^3– , das bei 282 nm eine schwache Absorption aufweist und parallel zum Erscheinen von Fe(CN) ₆ ^3– verschwindet. Man beobachtet eine drastische Änderung in der Oxidationskinetik, wenn das HOCl/Fe(CN) ₆ ^4– Konzentrationsverhältnis vonR>1 zuR<1 verändert wird. In Abhängigkeit vonR wird offenbar entweder Fe(CN) ₆ ^4– oder HOCl durch das Intermediat oxidiert. FürR1 erscheint ein weiteres Intermediat mit einer starken Absorptionsbande bei 360 nm, das ebenfalls der Oxidation vorangeht. Bei den beobachteten Intermediaten handelt es sich vermutlich um reaktive höhere Oxidationsstufen des Eisens (Fe(IV) und Fe(VI)). Die HOCl-induzierte Oxidation von Fe(CN) ₆ ^4– wird einerseits durch Br^–, I^– und N ₃ ^– katalytish aktiviert (offenbar infolge der Bildung stärkerer Oxidantien wie HOBr, HOI und ClN₃), andererseits durch CN^– und NCS^– effektiv inhibiert.

     

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.