Kinetics and mechanism of exchange of cyanide in hexacyanoferrate(II) by N-methylpyrazinium ion in the presence of mercury(II) as a catalyst

The kinetics of the mercury(II) catalysed ligand exchange of the hexacyanoferrate(II) complex with the N-methylpyrazinium ion (Mpz⁺) in a potassium hydrogen phthalate buffer medium has been investigated at 25.0 ± 0.1 °C, pH = 5.0 ± 0.02 and ionic strength, I = 0.1 M (KNO₃). The reaction was followed spectrophotometrically in the aqueous medium by measuring the increase in absorbance of the intense blue complex [Fe(CN)₅Mpz]^2– at its _max 655 nm. The effect of pH, and the concentrations of [Fe(CN)₆ ^4–] and Mpz⁺ on the reaction rate have been studied and analysed. The varying catalytic activity of mercury(II) as a function of concentration has also been explained. The kinetic data suggest that substitution follows an interchange dissociative (I _d) mechanism and occurs via formation of a solvent-bound intermediate. The effects of the dielectric constant of the medium on the reaction rates have been used to visualize the formation of a polar activated complex and an interchange dissociative mechanism for the reaction. A mechanism has been proposed in order to interpret the kinetic data. Kinetic evidence is reported for the displacement of CN^– by Mpz⁺ in [Fe(CN)₆ ^4–]. Activation parameters for the catalysed and uncatalysed reaction have been evaluated, and lend further support to the proposed mechanism.     

Trigonal kristallisierende Metall(II)-hexacyanoferrate(II)M2II[Fe(CN)6]

Trigonal Crystallizing Metal(II) Hexacyanoferrates(II) M₂^II[Fe(CN)₆] According to X-ray powder diagrams, Ca₂[Fe(CN)₆], Cd₂[Fe(CN)₆], Zn₂[Fe(CN)₆] · 2 H₂O, Pb₂[Fe(CN)₆] and the firstly described compounds Zn₂[Fe(CN)₆] · 2 NH₃ and Sn₂[Fe(CN)₆] crystallize trigonal containing one formula unit in the unit cell. Ca₂[Fe(CN)₆] and Cd₂[Fe(CN)₆] are belonging to the space group D—P3 1m, the other compounds to D—P3 m1. The latters are described as coordination polymers with a coordination number 4 for Zn and 3 for Sn and Pb, respectively.     

Ion pairing and the rate of the reaction between hexacyanoferrate(II) and octacyanotungstate(V) ions

The rate of the reaction Fe(CN) ₆ ^4– +W(CN) ₈ ^3– Fe(CN) ₆ ^3– +W(CN) ₈ ^4– in aqueous solution has been studied at various temperatures and ionic strengths, in the presence of Group IA cations. The results, combined with earlier work on the ion pairing of these compounds, give an indication of the number of cations present in the activated complex, a number which increases steadily in going from Li⁺ to Cs⁺ as the associated cations. Activation parameters for the reaction at various total [M⁺] are also evaluated.     

Complexing of Cu(II) with N,N'-Diphenylthiooxamide and N,N'-Diphenyldithiooxamide in a Gelatin-Immobilized Cu2[Fe(CN)6] Matrix

A study was made of complexing in Cu(II)-N'N'-diphenylthiooxamide, Cu(II)-N'N'-di-phenyldithiooxamide systems in gelatin-immobilized Cu₂[Fe(CN)₆] matrices brought into contact withaqueous alkaline (pH 12.0±0.1) solutions of these ligands. In both cases, complexing is preceded by alkaline breakdown of copper(II) hexacyanoferrate(II) into Cu(II) hydroxide or oxohydroxide which is the species reacting with the ligands. In each system, complexing yields a Cu(HL)2 chelate (HL^- is the single-deprotonated form of N,N'-diphenylthiooxamide or N,N'-diphenyldithiooxamide).     

Binding of hexacyanoferrate(II) by aliphatic amines in aqueous solution

The stability of hexacyanoferrate(II)-amine(methylamine, ethylenediamine, diethylenetriamine and tetraethylenepentamine) was determined potentiometrically. Species Fe(CN)₆(A)H _j ^(j–4) (A=amine) are formed in all the systems investigated, with j=1...n+2 (n=number of aminogroups). Some other complexes Fe(CN)₆(A)_iH_j (with i>1) were also found. The stability of these complexes is fairly high: the full protonated amine species, show for the reaction Fe(CN)₆ ^4- + H_nAⁿ⁺ = Fe(CN)₆(A)H_n ^(n-4) an equilibrium constant given by logK=0.686+2.10n. Factors affecting the stability are discussed in comparison with similar systems, together with the importance of interferences.     

Potassium bis(ethylenediamine)­copper(II) ferricyanide

The title compound, potassium bis(ethylenediamine‐N,N′)copper(II) hexacyanoferrate(III), K[Cu(C₂H₈N₂)₂]‐[Fe(CN)₆], contains [Cu(en)₂]²⁺ and [Fe(CN)₆]^3? complex ions, where en is ethylenediamine. The Fe^III and K⁺ ions lie on twofold axes and the Cu^II atom lies on an inversion center. The [Cu(en)₂]²⁺ ion has square‐planar coordination with a mean Cu—N distance of 1.992 (2) Å and the [Fe(CN)₆]^3? ion has distorted octahedral coordination with a mean Fe—C distance of 1.947 (2) Å.     

Structure of copper-potassium hexacyanoferrate (II) and sorption mechanisms of cesium

A mixed potassium-copper hexacyanoferrate (II) K₂CuFe(CN)₆ was prepared by local growth on solid cupric sulfate in an aqueous solution of potassium hexacyanoferrate (II) and by growth in a gel. Powders having this composition and separable by filtration could not be obtained by normal precipitation from aqueous solution. This compound has a triclinic P-1 structure, described for the first time, and made up of non-linear -Fe-C-N-Cu-chains which form a puckered layered network. Sorption mechanisms for cesium have been studied in batch experiments including kinetics and isotherms, X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. In neutral solutions the initial crystal structure is maintained and sorption proceeds through a K/Cs ion exchange. In acid solutions, even without addition of cesium, the initial structure is destroyed. The main phase formed in acidic media is Cu₂Fe(CN)₆. In the presence of cesium the structure is also destroyed and new solid phases are formed. All these processes have slow kinetics, the evolution of the solid being observed over a period of 6 months. This study confirms previous results, which have shown that the sorption mechanisms on hexacyanoferrates strongly depend on the composition and structure of the solid, together with the composition of the solution. Sorption mechanisms have considerable consequences on the use of these products for the decontamination of radioactive wastes.     

Iron(II)-8-mercaptoquinoline,iron(II)-5-chloro-8-mercaptoquino-line and iron(II)-5-bromo-8-mercaptoquinoline complexing in the iron(III) hexacyanoferrate(II) gelatin-immobilized matrix systems

Novel complexing processes in the Fe^II-8-mercaptoquinoline, Fe^II-5-chloro-8-mercaptoquinoline and Fe^II-5-bromo-8-mercaptoquinoline systems, not used previously in coordination chemistry, namely complexing as an iron(III)hexacyanoferrate(II) gelatin-immobilized matrix (GIM) in contact with an aqueous solution of the corresponding ligand, have been observed and analysed. Incorporation of these ligands into the inner coordination sphere is preceded by the decomposition of the immobilized compound KFe[Fe(CN)₆] to form hydroxides or oxohydroxides of Fe^II and Fe^III under the action of OH^- ions. It has been shown that Fe^IIFeIII redox process and the formation of FeB₃ chelates (B^- is a singly deprotonated form of the corresponding ligand) take place during complexing under such conditions.     

Copper(II) and nickel(II) metallopolymers derived from polyacylhydrazones

A series of polyacylhydrazones derived from condensing diacetyl with oxalic, malonic, succinic, glutaric and adipic dihydrazides was prepared, characterized and reacted with copper(II) and nickel(II) acetate to give metallopolymers of general formula [Cu₂(L)(AcO)₂(OH)(H₂O)₂] · yH₂O _n , [Cu(L)(AcO)(HO)(H₂O)] · yH₂O _n , [Ni₂(L)(AcO)₂-(HO)₂] · yH₂O _n and [Ni(L)(AcO)(HO)] · yH₂O _n , where L refers to the neutral dihydrazone unit. Magnetic susceptibility measurements in the 4.2–300 K range indicate significant antiferromagnetic coupling between the Cu^II centers in the metallopolymers, which may indicate the presence of two polymer chains crosslinked by bis--acetatocopper(II) bridges. Based on i.r., spectral and magnetic measurements, tentative structures of the Cu^II and Ni^II metallopolymers have been proposed. The dihydrazone units in these polymers are coordinated to the metal(II) via the azomethine nitrogen(s) whereas the amide group remains uncoordinated. Each Cu^II is penta-coordinated in a distorted square pyramidal environment and is neutralized by one bridged acetate and a hydroxide ion, while the fifth coordination site is occupied by a water molecule. In the nickel(II) metallopolymers the metal ions are in a tetrahedral environment and are coordinated to azomethine nitrogen, two bridged acetate oxygens and to the hydroxide ion.     

Complexation in Binary Cd2[Fe(CN)6]–M(II) Systems (M = Mn,Co, Ni,Cu, Zn) in Gelatin-Immobilized Cadmium(II) Hexacyanoferrates(II)

Complexation processes that occur between cadmium(II) hexacyanoferrate(II) (Cd₂[Fe(CN)₆]) and 3d-metal ions M(II) (M = Mn, Co, Ni, Cu, Zn) in thin gelatin layers with the immobilized cadmium(II) hexacyanoferrates when brought in contact with aqueous solutions of d-metal chlorides are studied. Cd²⁺ ions were found to be replaced to some extent by M²⁺ ions of the indicated d metals (except for Mn(II)) and form binuclear (dd)-metal hexacyanoferrates(II). A complete replacement of Cd(II) and formation of M₂[Fe(CN)₆] was observed in none of the cases.     

Kinetics of reactions of the tris(2,2′-bi(4H-5,6-dihydrothiazine))iron(II) cation

Summary We report rate constants for reactions of tris(2,2-bi(4H-5,6-dihydrothiazine)iron(II), Fe(btz) ₃ ²⁺ , in acid solution, with hydroxide, with peroxodisulphate, with silver(I), with mercury(II), and with cadmium(II), in aqueous solution, and for the reaction of Fe(btz)_{3 3} ²⁺ with 1,10-phenanthroline and with 2,2-bipyridyl in aqueous methanol. Mechanisms and relative reactivities are discussed.     

Synthesis and properties of cyano-bridged nickel(II)-iron(III) complexes

Summary Four kinds of novel CN-bridged Ni^II-Fe^III complexes, [NiLn(NC)Fe(CN)₅] ^–, have been synthesized and characterized by elemental analysis, i.r. and u.v.-vis. spectral analysis, and magnetic moments. The formation of cyanide bridges is evident from the i.r. and u.v.-vis. spectra by the appearance of v(CN) shifts and changes in _max with respect to the mononuclear parent complex [Fe(CN)₆]^3–. The magnetic properties indicate the existence of magnetic spin interactions between Ni^II and Fe^III through the cyanide bridge.     

The dynamic behaviour of the silver-silver hexacyanoferrate(II) electrode: coulometric production of hexacyanoferrate(II)

The electrochemical behaviour of the silver-silver hexacyanoferrate(II) elec-trode was studied. The reaction Ag₄[Fe(CN)₆] + 4e^- → 4Ag + [Fe(CN)₆]^4- was shown to be useful for the coulometric production of hexacyanoferrate(II) ions in titrations of zinc(II). Coulometric titrations of organometallic compounds such as R₂Sn(ClO₄)₂, with electrically generated hexacyanoferrate(II) are also reported.     

Complexing processes on the immobilized matrices of hexacyanoferrate(II)-nickel(II) and nitrogen-sulfur ligands in thin gelatin layer

Summary Complexing processes occurring between immobilized matrices obtained from Ni(II) hexacyanoferrates(II) and solutions of various nitrogen-sulfur-containing chelating ligands in thin gelatin layers have been studied. With Ni₂[Fe(CN)₆]-matrix, the complexing process is found to proceed according to a S _N ² -mechanism. The schemes of the processes in each of the above matrices are given. Examples of kinetic curves for particular systems hexacyanoferrate(II) nickel(II)-ligand are presented.

---

Komplexierungsprozesse auf den immobilisierten Matrices von Hexacyanoferrat(II)-Nickel(II) und Stickstoff-Schwefel-Liganden in dünnen Gelatin-Schichten

Zusammenfassung Es wurden Komplexierungsprozesse auf immobilisierten Matrices, die von Ni(II)-Hexacyanoferrat(II) und Lösungen verschiedener Stickstoff-Schwefel-Liganden erhalten wurden, in dünnen Gelatin-Schichten untersucht. Mit einer Ni₂[Fe(CN)₆]-Matrix wurde festgestellt, daß der Komplexierungsprozeß nach einem S _N ² -Mechanismus verläuft. Es werden die entsprechenden Reaktionsschemata angegeben. Beispiele für den kinetischen Verlauf für bestimmte Hexacyanoferrat(II)-Ni(II)-Ligand-Systeme werden präsentiert.

     

Trans-bis(dicyanamido)nickel(II) complexes with polyaza macrocyclic ligands

Two new trans-bis(dicyanamido)nickel(II) macrocyclic complexes, [Ni(II)(L1){N(CN)₂}₂] · H₂O (1) and [Ni(II)-(L3){N(CN)₂}₂] (2), where L1 is 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane and L3 is 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane, have been synthesized and structurally characterized by spectroscopic and X-ray crystallographic methods. In (1) and (2), each central nickel(II) ion possesses a distorted octahedral geometry with four equatorial nitrogen atoms from the macrocycle and two axial nitrogen atoms from dicyanamide anions, which are terminally bonded to the central nickel atom. The solid state electronic spectra of (1) and (2) using the diffuse reflectance method show a characteristic high-spin d⁸ nickel(II) ion in a distorted octahedral environment.     

Adsorption characteristics of radionuclides on nickel hexacyanoferrate(ii)

The composition of nickel hexacyanoferrate(II) complexes depends on the ratios of sodium hexacyanoferrate(II) and nickel nitrate solutions mixed. The adsorption behavior of nickel hexacyanoferrate(II) is described; acid treatment of Ni₂Fe(CN)₆ accelerates the adsorption rate of cesium, but does not increase the adsorption capacity. The Ni—Cs exchange ratios of Ni₂Fe(CN)₆ are discussed. In concentrated salt solutions, the distribution coefficients of ⁵⁹Fe, ⁶⁰Co, ⁶⁵Zn. ¹³⁷Cs, ⁹⁵Zr and ¹⁴⁴Ce are determined together with those of ⁸⁵Sr and ¹⁰⁶Ru. A simple determination of ¹³⁷Cs in sea water containing ⁵⁹Fe, ⁶⁰Co, ⁶⁵Zn, ⁹⁵Zr, ¹⁴⁴Ce, ⁸⁵Sr and ¹⁰⁶Ru is described.     

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.     

A bimetallic cyano-bridged complex based on nickel(II) and pentacyanidonitrosylferrate(II) precursors: characterization, crystal structure, and magnetic properties

A heterobimetallic cyano-bridged 1D coordination polymer of the composition [Ni(baepn)(μ-NC)Fe(CN)₃(NO)(μ-CN)]_n·3H₂O has been synthesized by the reaction of nickel(II) nitrate hexahydrate, baepn (baepn = N, N′-bis(2-aminoethyl)-1,3-propanediamine), and sodium nitroprusside dihydrate in a methanol–water mixture. The complex was characterized by physicochemical and spectroscopic methods. The crystal structure was established by single-crystal X-ray diffraction analysis. It reveals cyano-bridged heterometallic chains consisting of alternating arrays of Ni(II) and Fe(II) atoms, both being embedded in distorted octahedral environments. Low-temperature susceptibility measurements show the presence of weak antiferromagnetic exchange interactions between paramagnetic Ni(II) centers (J = −0.46 cm⁻¹) through long diamagnetic [Fe(CN)₅(NO)]²⁻ bridges. Spin state of the iron atom was established by ⁵⁷Fe M?ssbauer spectroscopy.     

Complexation en solution aqueuse des ions magnesium(II), manganese(II), nickel(II), cuivre(II) et plomb(II) avec la s-carboxymethyl-l-cysteine: Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution

Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution.The complex formation between Mg(II), Mn(II), Ni(II). Cu(II), Pb(II) ions and S-carboxy-methyl-l-cysteine (H₂A) has been studied by measurement of pH at 25°C and constant ionic strength (1 M NaClO₄). Although no interaction occurs with Mg(II), this work provides evidence for a variety of complexes: MnA; CuHA⁺; CuA; CuA₂^2-; NiHA⁺; NiA; NiA₂^2-; PbHA⁺; PbA et PbA(OH)^-. The overall formation constants of all these species are computed and refined. The results allow the determination of the distribution of the complexes as a function of pH; some structural features of the metal complexes in solution are indicated.