Formation Of Polynuclear Complexes Research Articles

Optimal acidity of complexes by solution of polynomials and by iteration

The methods for optimal acidity of complexes M x L y (OH) m H n based on direct iteration or solution of polynomials are described and discussed. Then, by a direct straightforward method of computation (that does not require any iteration) the complexes M x L(OH) m H n and ML y (OH) m H n are treated (where 1 ⩽ x ⩽ 3 and 1 ⩽ y ⩽ 3). Finally, the conditions leading to formation of polynuclear complexes are shown and discussed. The importance of study of polynuclear complexes for solving of biochemical problems is pointed out. Practical examples are given for each method.

Characterisation of the predominant low-pH lead(II)–hydroxo cation, [Pb4(OH)4]4+; crystal structure of [Pb4(OH)4][NO3]4and the implications of basic salt formation on the transport of lead in the aqueous environment

A study of the reactions between PbII and hydroxide ions in aqueous nitrate solutions has identified three distinct basic salt phases. When the pH is raised, the first precipitate obtained from the Pb2+–NO–3–H2O system is the [Pb4(OH)4]4+ cluster cation. The crystal structure of [Pb4(OH)4][NO3]4 has been determined by single-crystal X-ray diffraction and refined by full-matrix least-squares analysis to R1= 0.0706, wR2= 0.1827. The complex crystallises in the monoclinic space group la, with a= 18.251(5), b= 17.206(5), c= 18.588(12)A, β= 91.90(4)° and Z= 16. The PbII atoms are contained within discrete [Pb4(OH)4]4+ units. The four lead atoms are situated at the corners of a distorted tetrahedron with an average Pb–Pb distance of 3.785(4)A and an average intracluster Pb–Pb–Pb bond angle of 60.0(1)°. The OH groups are situated above the faces of the Pb4 tetrahedron giving each Pb atom a trigonal-pyramidal arrangement of nearest-neighbour oxygen atoms. The average Pb–OH distance is 2.38(7)A and the average OH–Pb–OH angle 71.8(2)°. The next-nearest Pb–O distances are to nitrate O atoms with the shortest of these being in the range 2.62–2.80 A suggesting that the non-bonding electron pairs on Pb point outwards from the cluster and cannot take part in lead–lead cluster interactions. The Raman data for the [Pb4(OH)4]4+ cluster have been correlated with the crystal structure. The thermal decomposition of [Pb4(OH)4][NO3]4 has been studied and is rationalised in terms of a two-step dehydration of the [Pb4(OH)4]4+ ion, followed by a four-step decomposition of the nitrate-containing compounds. The formation of polynuclear complexes may also depend on the total lead(II) concentration but there is no evidence from the present work for the precipitation of any phase other than [Pb4(OH)4][NO3]4 in the initial precipitates. Under the conditions studied, increase of the pH above 5.25, after the precipitation of [Pb4(OH)4][NO3]4, resulted in the replacement of NO3– in the lattice by OH– and the formation of distinct phases at pH ca. 7 and 8.5 that are likely to be based on [Pb3(OH)4]2+ and [Pb6O(OH)6]4+ respectively. The implications of the formation of the Pb–OH clusters on the transport of lead in the aqueous environment have been discussed.

The temperature dependence of stability constants for the formation of polynuclear cationic complexes

The temperature dependence of the formation of polynuclear cationic complexes is analyzed on the basis of a simple electrostatic model of electrolytic dissociation proposed by Ryzhenko and Bryzgalin . It is possible to expand this theory to the case of polynuclear cationic complexes, considering the formation of such complexes as a result of two competing processes: a nonelectrostatic attraction and an electrostatic repulsion of the spheres consisting of mononuclear “building blocks.” The relative stability of polynuclear complexes decreases with temperature because of the large increase of electrostatic repulsion due to the decrease of the dielectric constant of water. The predictive properties of the model is exemplified by the system Al+3-OH−, where it is possible to describe the temperature dependence of stability constants for both mononuclear and polynuclear complexes up to 200–250°C at saturation water vapor pressure using the values of log Ko(298, 1) and only one fitting parameter a, which has the same value for all complexes in the system Al+3-OH−(a is close to the metal-hydroxide/oxide bond distance). Additional experimental data for the formation of polynuclear hydroxide complexes of divalent Mg, Co, Ni, Pb, and UO22+ confirmed the predictive properties of the model. The proposed model may be used to estimate entropies of hydrolysis reactions. These turn out to follow the empirical correlations previously established by Baes and Mesmer (1976) very well.

Equilibrium and Structural Studies on Metal Complexes of Oxime Ligands. Polynuclear Complex Formation of Copper(II) with 3-Aminopropanamidoxime and its N-Alkyl Derivatives.

Equilibrium and Structural Studies on Metal Complexes of Oxime Ligands. Polynuclear Complex Formation of Copper(II) with 3-Aminopropanamidoxime and its N-Alkyl Derivatives.

The formation of polynuclear stepwise complexes of nickel(II) with azide ions

The Ni II/N − 3 system was analysed. Equilibrium studies were performed at 25.0±0.1°C and 2.0 M ionic strength was maintained with NaClO 4. Extensive polynuclear complex formation was observed and the following stability constants, β pq , corresponding to [Ni p (N 3) q ] 2 p–q , were obtained: β 11 = 5.8; β 12 = 9.7; β 13 = 7.5; β 14 = 5.3 × 10 2; β 21 = 4.1; β 22 = 3.2 × 10; β 23 = 1.7 × 10 2; β 24 = 2.1 × 10 4; β 25 = 2.3 × 10 5; β 26 = 7.2 × 10 5; β 34 = 2.3 × 10 4; β 35 = 3.5 × 10 6 and β 36 = 1.2 × 10 8. This behaviour is different from zinc(II), copper(II), cadmium(II) and cobalt(II) where only mononuclear species were found.

Interaction of iron polymers with blood mononuclear cells and its detection with the Prussian Blue reaction

An inhibitory effect of iron salts on various immune functions in vitro has been reported in several laboratories during the last few years. This study confirms and extends those observations by showing that iron citrate inhibits the mitogen-induced (PHA, Con A and PWM) lymphocyte proliferation. Such inhibition is observed in the presence of ferric citrate with a metal-to-ligand molar ratio of I : I but not with ferric citrate with metal-to-ligand molar ratio 1:20 in which the formation of polynuclear iron complexes is prevented. Increasing the concentration of serum in the culture medium diminished the inhibitory effect of 1:1 ferric citrate. Using the Prussian Blue reaction the presence of ferric iron was observed on the cell surface. It is proposed that the deposition of polynuclear iron complexes on the lymphocytes membrane is one of the possible factors determining the iron inhibitory effect.

Synthesis and coordination chemistry of 1-(2′,2″-bipyridyl-5′-yl-methyl)-1,4,8,11-tetraazacyclotetradecane L1. Quenching of fluorescence from [Ru(bipy)2(L1)]2+by coordination of NiIIor CuIIin the cyclam cavity (bipy = 2,2′-bipyridine; cyclam = 1,4,8,11-tetra-azacyclotetradecane)

A novel bipy derivative of cyclam (L1) designed for controlled and systematic polynuclear metal complex formation is reported; fluorescence quenching of the [Ru(bipy)3]2+ core of [(bipy)2Ru(L1)]2+ upon coordination of CuII at the cyclam cavity is demonstrated.

A calorimetric study of the Ni(II)‐5′AMP system

The thermodynamic parameters of the interaction between Ni(II) (M) and 5'-AMP in aqueous solution were determined calorimetrically (I = 0.1 tetramethylammonium bromide, 25 degrees C) at physiological pH. The experimental conditions were carefully selected to avoid the polynuclear complex formation. From the Ni(5'AMP)-complex-formation constant (logK1 = 2.55), the Ni(5'AMP)2(2-)-complex-formation constant and the Ni(5'AMP) (ML) and Ni(5'AMP)2(2-) (ML2) complex-formation enthalpies were determined (logK2 = 2.34, delta H1 = -10.0 kJ/mol and delta H2 = 21.6 kJ/mol). These results confirm the formation of the ML2 complex in solution and agree very well with the hypothesis of the 'stacking' between the purine rings, promoted for metal ions.

Aqueous silver-triazolium thiolate complexes

The formation of mononuclear and polynuclear aqueous silver complexes of 4-substituted-1,5-dimethyl-1,2,4-triazolium-3-thiolates was determined by titrations and then analyzed with a Monte-Carlo-based algorithm developed to fit a model for competitive equilibria to titration data. The apparent stability constants, β nm , for Ag n L n+ m complex formation (β 11, β 12, β 13, β 23, β 34) are tabulated for various thiolates, L, at 23° C and at an ionic strength μ = 0.1 M in KNO 3. These Ag +-triazolium thiolate complexes form with a strength that is intermediate between those of the strong Ag +-thiosulfate complexes and the weaker Ag +-thione complexes. The polynuclear Ag 2L 2+ 3 complex dominates in ligand-rich solutions of the triazolium thiolates, in contrast to the mononuclear Ag(S 2O 3) 3− 2 complex, which predominates over the other complexes in thiosulfate-rich solutions.

Construction of Multicomponent Pourbaix Diagrams Using Generalized Species

A method for the construction of predominance‐zone diagrams of multicomponent and multiphase systems of chemical species in a single oxidation state, which consider the formation of mixed and polynuclear complexes (of the type) is presented. Such diagrams may be constructed by defining generalized species, complexation coefficients (with multiplicative structure) and generalized equilibria of complexation, dismutation, polynucleation, and phase formation, with their conditional constants associated. By having these diagrams for each oxidation state of the same component, multidimensional Pourbaix diagrams are constructed. The predominance‐zone diagrams of *Eu(0), *Eu(II), and *Eu(III) in the presence of citric acid and nitrilotriacetic acid in aqueous solution, are constructed by using this approach.

Hydrolysis of aluminum(III) ion in sodium nitrate medium

Hydrolysis of aluminum(III) ion in 3.0 M (Na)NO3 medium was studied by emf method at 25° C. Data cover the range 1–78 mM Al(III) within the pH range of 2.0–4.5. At a definite pH, the extent of hydrolysis increases with increasing aluminium concentration, thereby indicating the presence of polynuclear hydrolysis products. The least squares treatment of the data indicates the formation of polynuclear hydrolytic complexes [Formula: see text] [Formula: see text] and [Formula: see text] With the reactions written in the form[Formula: see text]the stability constants obtained were log (β2,2 = −7.55 ± 0.21, log β2,4 = −16.41 ± 0.13, and log (β3,4 = −13.24 ± 0.08. Distribution curves indicate that the complex [Formula: see text] is predominant. Key words: hydrolysis, aluminum(III) ion, hydrolytic complexes, aluminum(III) ion hydrolysis.

ChemInform Abstract: Metal Complexes of Small Cycloalkynes and Arynes

Cyclooctyne is the smallest unsubstituted cycloalkyne that can be isolated in the free state and it is more reactive than acyclic alkynes towards transition metal complexes. Smaller cycloalkynes such as cycloheptyne, cyclohexyne, benzyne and cyclopentyne, which are transient molecules in the free state, can be stabilized by coordination either to mononuclear, electron-rich, transition metal-containing fragments, e.g. [ZrCp2(PMe3)] and M(PR3)2 (M = Ni, Pt), or by formation of dinuclear or polynuclear metal complexes, e.g. [Os3H2(CO)9(C6H4)] and [Pt2(μ-PPh2)(μ-C5H6)(PPh3)3]. The alkynes can donate between two and four π-electrons to the metal centers, the higher number being favored for the early transition metals. The metal-cycloalkyne and metal-aryne bonds in the mononuclear complexes readily insert molecules containing CO, CC, CC and CN bonds, a feature that may be useful in organic synthesis. The highly unsaturated species 1, 4-benzdiyne acts as a bridging ligand between two metal centers in [{Ni(Cy2PCH2CH2PCy2)}2(μ-C6H2)].

Polynuclear thiolate complexes in solution. Solution equilibria studies of silver(I) complexes of 4-mercapto-1-methylpiperidine

Polynuclear complex formation at 25 °C in 2 mol dm–3 NaNO3(10% v/v MeOH) between Agl and 4-mercapto-1-methylpiperidine has been studied by means of two different sets of titrations. The first set allows one to establish that [Agp(AH)q]p+ species with the p,q values 12,12; 10,9; 8,6; 7,6; 6,4; and 6,3 are present in strongly acidic solutions, AH being the monoprotonated ligand. The second set indicates that at increasing pH values, pH ⩽ 8.5, the only species with p=q, [Ag12(AH)12]12+, coexists and eventually transforms into complexes with p < q: 7,8; 6,8; 2,3; and 1,3. In both cases, graphical methods were applied prior to the mathematical treatment of data. An adaptation of the extended-variation method to metal electrode data has been carried out.

A potentiometric study on the complexation between mercury(II) and phenolate ions

The stepwise stabilities of the complexes formed by mercury(II) with the phenolate and p-nitrophenolate ions have been determined potentiometrically in an aqueous sodium perchlorate medium of unit ionic strength at 25.0°C. In both of the systems studied, only the strong, mononuclear complexes were formed in the range of concentrations used. No evidence has been found for the formation of polynuclear and/or acid complexes.

Formation of Nitrite Complexes of Gallium(III) and Indium(III) in Aqueous Solution

Abstract Stepwise complex formation between gallium(III), indium(III) and nitrite ions has been studied potentio-metrically by means of a glass electrode in an aqueous sodium perchlorate medium of unit ionic strength at 25.0°C. In both systems only mononuclear complexes of moderate stability were formed over the range of concentrations used. No evidence has been found for the formation of polynuclear and/or acid complexes. Values of the overall constants for the formation of Ga(NO2)2+ In(NO2)2 +, In(NO2)2 and In(NO2)3 are 130 ± 40M−1, 390 ± 110M−1, (1.04 ± 0.29)104 M−2, and (8 ± 5)104 M−3, respectively.

Metal Complexes of Small Cycloalkynes and Arynes

AbstractCyclooctyne is the smallest unsubstituted cycloalkyne that can be isolated in the free state and it is more reactive than acyclic alkynes towards transition metal complexes. Smaller cycloalkynes such as cycloheptyne, cyclohexyne, benzyne and cyclopentyne, which are transient molecules in the free state, can be stabilized by coordination either to mononuclear, electron‐rich, transition metal‐containing fragments, e.g. [ZrCp2(PMe3)] and M(PR3)2 (M = Ni, Pt), or by formation of dinuclear or polynuclear metal complexes, e.g. [Os3H2(CO)9(C6H4)] and [Pt2(μ‐PPh2)(μ‐C5H6)(PPh3)3]. The alkynes can donate between two and four π‐electrons to the metal centers, the higher number being favored for the early transition metals. The metal‐cycloalkyne and metal‐aryne bonds in the mononuclear complexes readily insert molecules containing CO, CC, CC and CN bonds, a feature that may be useful in organic synthesis. The highly unsaturated species 1, 4‐benzdiyne acts as a bridging ligand between two metal centers in [{Ni(Cy2PCH2CH2PCy2)}2(μ‐C6H2)].

Raman spectra of zeolites exchanged with uranyl(VI) cations—I. Zeolite Y

UO 2Y zeolites prepared by various methods have been characterized by Raman spectroscopy. The speciation of [UO 2] 2+ cations in as-prepared zeolites was found to be determined by hydrolytic reactions occurring at the zeolite—solution interface during ion-exchange, which resulted in the formation of hydroxy-bridged polynuclear complexes in all zeolites investigated. The extent of cation hydrolysis was found to be significantly reduced if the parent NaY zeolites were pretreated in mildly acidic media prior to ion-exchange, and a model for the chemical processes occurring during sample preparation is proposed.

Study of the interaction of [Cu(bipy)]2+ with oxalate and squarate in aqueous solution

A study of the formation of complexes between [Cu(bipy)]2+ and ox2− and sq2− in aqueous solution, (bipy being 2,2′-bipyridine and ox2− and sq2− the dianions of ethanedioic acid and 3,4-dihydroxy-3-cyclobutene-1,2-dione, respectively), has been carried out with the aim of comparing the coordinating properties of these related ligands. The constants of the equilibria (i) and (ii) $$[Cu(bipy)]^{2 + } + ox^{2 - } \rightleftharpoons [Cu(bipy)ox]$$ (i) $$[Cu(bipy)]^{2 + } + sq^{2 - } \rightleftharpoons [Cu(bipy)sq]$$ (ii) have been determined by potentiometry and spectrophotometry at 25.0°C and 0.1 M NaNO3:logβ=5.78(2) and 2.16(2) for the oxalato- and squarato-complex, respectively. Such different values reveal that these related ligands coordinate to copper in a different fashion, as has been shown recently by x-ray diffraction studies. Polynuclear complex formation was not observed in solution in our experimental conditions for either system.

Second sphere donor acceptor interactions in excited states of coordination compounds. Ruthenium(II) bipyridine cyano complexes

Abstract

ChemInform Abstract: A General Synthetic Route for Platinum Cluster Compounds Containing Carbonyl and Tertiary Phosphine Ligands and a Study of Their Reactions with Unsaturated Inorganic Molecules.

AbstractThe reduction of complexes such as (I) by zinc dust or NaBH4 in MeOH or acetone under a CO atmosphere is an efficient method for the formation of polynuclear complexes (II)‐(IV) which is superior in yield convenience and generality to other methods and applicable for compounds (I) containing tert. phosphine ligands with a variety of alkyl or aryl groups.