Effect of solvent on the reactions of coordination complexes: Part 16. Kinetics and mechanism of complexation of oxalatopentaammine-cobalt(III) with nickel(II) in methanol-water medium

The kinetics of reversible complexation of oxalatopentaammine cobalt(III) with Ni²⁺ has been investigated in MeOH + water media (0–50 (v/v) % MeOH) at 15.0–35.0°C and I = 0.10 mol dm^?3. Analysis of rate data indicates that the monobonded complex [(NH₃)₅ · CoOCOCO₂Ni]³⁺ in which Ni²⁺ is bound to the end carboxylate group is the possible reaction intermediate. The formation and dissociation rates of such a species are rate limiting for the overall formation and dissociation of the binuclear species, in which Ni²⁺ is chelated by the oxalate moiety. The rate and activation parameters for formation and dissociation of the binuclear species are moderately solvent sensitive and solvent structural effects are discernible in the nonlinear variations of ΔH^≠ and ΔS^≠ with solvent composition. The log k_r vs. Grunwald Winstein parameter (Y) plot for the dissociation of the binuclear species is markedly nonlinear.     

Acceptor power of cations in donor-acceptor interactions

Published data concerning quantitative evaluation of the reactivity of cations in donor-acceptor interactions were analyzed. The “relative acceptor numbers” of C°²⁺, Mn²⁺, Ni²⁺, Al³⁺, and Ga³⁺ were determined polarographically: 2.16±0.32, 2.25±0.23, ～1.70, 2.35±0.27, and 2.42±0.21, respectively. The known “relative acceptor numbers” for 21 cations were systematized, and a linear correlation between the ionization potentials and “relative acceptor numbers” of “hard” cations was revealed.     

Synthesis of polyacrylonitrile by single‐electron transfer‐living radical polymerization using Fe(0) as catalyst and its adsorption properties after modification

Fe(0) was firstly used as single‐electron transfer‐living radical polymerization catalyst for acrylonitrile polymerization using carbon tetrachloride as initiator, hexamethylenetetramine as N‐ligand, and N,N‐dimethylformamide as the solvent at 65 °C. First‐order kinetic studies indicated that this polymerization proceeded in a “living”/controlled manner. The living nature of the polymerization was also confirmed by chain extension of methyl methacrylate with polyacrylonitrile (PAN) as macroinitiator. Furthermore, PAN was modified with NH₂OH·HCl to generate amidoxime groups for extraction of heavy metal ions (Hg²⁺) from aqueous solutions. Fourier transformed infrared spectroscopy was performed to characterize chemical composition and structure. The adsorption property of Hg²⁺ was investigated at different pH values of aqueous solutions and distilled water. The maximal saturated adsorption capacity of Hg²⁺ was 4.8 mmol g^?1. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Hofmeister Effects of Group II Cations as Seen in the Unfolding of Ribonuclease A

This work studies the effects of alkaline-earth cation addition on the unfolding free energy of a model protein, pancreatic Ribonuclease A (RNase A) by differential scanning calorimetry analysis. RNase A was chosen because: a) it does not specifically bind Mg²⁺, Ca²⁺ and Sr²⁺ cations and b) maintains its structural integrity throughout a large pH range. We have measured and compared the effects of NaCl, MgCl₂, CaCl₂ and SrCl₂ addition on the melting point of RNase A. Our results show that even though the addition of group II cations to aqueous solvent reduces the solubility of nonpolar residues (and enhances the hydrophobic effect), their interactions with the amide moieties are strong enough to “salt-them-in” the solvent, thereby causing an overall protein stability reduction. We demonstrate that the amide-cation interactions are a major contributor to the observed “Hofmeister Effects” of group II cations in protein folding. Our analysis suggests that protein folding “Hofmeister Effects” of group II cations, are mostly the aggregate sum of how cation addition simultaneously salts-out hydrophobic moieties by increasing the cavitation free energy, while promoting the salting-in of amide moieties through contact pair formation.     

Decomposition of [NiRR′L2] complexes induced by bromine or anodic oxidation

A study has been made of the decomposition of the compounds t-[NiRR′L₂] (L = PMe₂Ph and PEt₃; R = aryl or vinyl groups) and [Ni(mes)(o-tol)bipy] (mes = mesityl) oxidatively induced either by electrochemical means or by bromine. No organometallic compound of Ni^III was isolated in the above reactions, but a pentacoordinate intermediate of Ni^III is postulated. Breakdown takes place readily after the Ni^III intermediate is formed. If the decomposition is induced electrochemically, the intermediate decomposes giving only the coupling product R-R′. When bromine is used as the oxidizing agent, the Ni^III intermediate is only formed if coordination to the central atom is allowed by the volume of the ligands. Thus, [Ni(C₂Cl₃)(mes)(PMe₂Ph)₂] does not decompose at all, and only [Ni(C₂Cl₃)(mesBr₂)(PMe₂Ph)₂] is obtained. The intermediate “Ni^IIIRR′BrL₂” undergoes reductive elimination to give R-R′, RBr and R′Br. The formation of the products R-R′ is increasingly favoured the greater the electronegativity of the organic ligands. The reductive elimination giving RBr takes place more readily the greater the electronegativity of the organic ligand R. The product of the reductive elimination reaction is “Ni^IBr”, “Ni^IR”, or “Ni^IR′”, which in the presence of bromine give Ni²⁺, [NiBr(RBr)L₂], phosphonium salts, RBr, and R′Br.     

Phase transitions in ferroic crystals of KMPO4(M=Fe2+, Co2+, Ni2+) studied by ODSC

The influence of the temperature program parameters of an ODSC experiment on the calculated “reversing” and “kinetic” signals has been studied. Mixed orthophosphate salts of KMPO₄ (where M=Ni²⁺, Co²⁺ and Fe²⁺) which present at least one structural phase transition have been used for this purpose. On these crystalline compounds we have shown that the non reversing heat flow is partly associated with the formation and disappearance of ferroelastic and ferroelectric domain walls. However a proper choice of the temperature program parameters is important so that the calculated “reversing” and “kinetic” curves have the supposed physical meaning according to the assumptions made for the calculations.     

Photocatalytic activity and physicochemical characteristics of modified potassium polytitanates in the reaction of decomposition of aqueous-alcoholic solutions

Study of the photocatalytic activity of nanomaterials based on potassium polytitanate modified with transition metal ions (Ni²⁺, Cr³⁺, Cu²⁺) demonstrated that the cation composition, morphology of photocatalyst particles, and their size strongly affect the photocatalytic activity. The rate of the photoinduced hydrogen evolution from the aqueous-alcoholic solution grows in the series of potassium polytitanates modified with Cu²⁺, Ni²⁺, Cr³⁺ ions, and that from pure water, for potassium polytitanates modified with Ni²⁺,Cr³⁺, Cu²⁺ ions. The capacity for intercalation of water into the interlayer space does not strongly affect the rate of the photoinduced hydrogen evolution. It was shown that potassium polytitanate modified with Cr³⁺ ions has the maximum quantum efficiency (30%).     

Kinetics of dissociation of tris-2,2′-bipyridyl-iron(II) cation in aqueous acetic acid solutions

The kinetics of dissociation of tris-2,2′-bipyridyl-iron(II) complex ion have been examined in aqueous acetic acid solutions. The reaction is first order in the complex ion; the dependence of rate on H⁺ is somewhat like that observed in aqueous solutions approaching a limiting value at higher H⁺ concentrations. The influence of solvent composition on the reaction rate under acid-dependent and acid-independent conditions shows an initial retardation by acetic acid. The argument of ion-pair formation based on decrease of dielectric constant proposed to explain the kinetics in other aqueous solvent media was found useless to explain the behavior in acetic acid solutions. Other solvent parameters also did not provide satisfactory correlation with the kinetic results, thus, indicating the operation of more complex microscopic solute-solvent and solvent-solvent interactions. While solvent effects play some part in the rate process, the rate of reaction would tend to zero in the absence of H₂O and H⁺. This interesting observation proved useful in proposing a reaction mechanism that is consistent with the rate behavior over the entire range of solvent composition. The activity of water in the reaction medium is controlled by the content of acetic acid which can effect the structure of water through operation of hydrophobic forces and formation of hydrates. While acetic acid cannot possibly fulfill the role of water in occupying the vacated coordination position, the anomalous rise in rate even under some water deficient conditions seems to be related to the coordinating ability of HSO₄^? derived from H₂SO₄ present in the solution.     

Stability of coordination compounds of Co2+ and Ni2+ ions with maleic acid anion in aqueous isopropanol solutions

Composition and stability of coordination compounds of nickel(II) and cobalt(II) ions with maleic acid anion in aqueous isopropanol solutions (H₂O-IPA) of composition χ_IPA = 0–0.5 mole fraction was studied by potentiometric titration at ionic strength of 0.1 maintained with sodium perchlorate at 298.15 K. Monoligand complexes of Ni²⁺ and Co²⁺ ions with maleic acid anion become stronger when isopropanol content rises. In the solvent of the studied composition, Co²⁺ ions form less stable complexes than Ni²⁺ ions that corresponds to the Irving-Williams series established for aqueous solutions. Variations in complex stability are more expressed at small IPA content and differ within experimental error at χ_IPA = 0.5 mole fraction. Obtained results were compared with literature data for akin compounds.     

Reaction of Ni2+ and SnS as a Way to Form Ni@SnS and Sn2Ni3S2 Nanocrystals: Control of Product Formation and Shape

Reductive diffusion of Ni²⁺ into SnS particles was shown to selectively form Sn₂Ni₃S₂, hybrid, or even core‐shell Ni@SnS, Ni_1.523Sn, and Ni₃S₂, by tuning the reaction conditions at low temperatures. The mechanism of Ni²⁺ reduction and diffusion into SnS was observed in ethylene glycol, which served both as solvent and reducing agent. Tuning of reaction temperature and duration, morphology of the template SnS, and the application of ethylenediamine as supporting chelating agent, influence the formation of the final products. Their formation was controlled by carefully adjusting redox and equilibrium reactions. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X‐ray spectroscopy analysis (EDX).     

EPR evidence of off-centred nickel at room temperature in NH4Cl

Electron paramagnetic resonance of γ-irradiated ammonium chloride single crystals doped with Ni²⁺ show the formation of Ni⁺ at orthorhombic sites at room temperature. The chlorine hyperfine structure clearly shows that nickel is at an off-centred interstitial position, lending support to the “off-centred impurity ion” model for the recently discovered spontaneous polarization in ammonium chloride.     

Metal Complexes with Macrocyclic Ligands. XV. The Complexation Kinetics of Open Chain and Cyclic Tetraazaligands with Ni2+ in DMSO and DMF

The complexation kinetics of 2,6,9, 13-tetraazatetradecane (1) , 1,4,8, 11-tetraazacyclotetradecane (2) and N,N′,N″,N'-tetramethyl-1,4,8, 11-tetraazacyclotetradecane (3) with Ni²⁺ were studied by the stopped-flow technique in DMSO and DMF. The biomecular rate constants k_L^Ni (Table 2) follow in both solvents the order 1 ? 2 > 3. The similar complexation rates of 1 and 2 in their unprotonated form indicate that for both the open chain and the cyclic ligand the same mechanism holds. By comparison with the solvent exchange the rate determining step of the complexation is the dissociation of the first solvent molecule in the outer-sphere complex. The lower reactivity of 3 is probably due to steric effects. In the case of 2 a second step in the complexation process was observed and explained by a rearrangement of the ligand already coordinated to the metal ion.     

Metal Complexes with Macrocyclic Ligands,V. Formation and dissociation kinetics of the pentaco-ordinated Ni2+, Cu2+, Co2+ and Zn2+ complexes with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane

The formation and dissociation kinetics of the pentaco-ordinated Cu²⁺, Ni²⁺, Co²⁺ and Zn²⁺ complexes with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (4-MeCyclam-14) was studied by pH-stat techniques and spectrophotometrically. The rates of the reactions between 4-MeCyclam-14 and each of the four metal ions, although slower than normal complexations by a factor of 10³?10⁴, closely follow the order Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺, found for the rate of water exchange. This implies that beside water exchange an other constant factor plays an important role in the rate determing step. The dissociation of the pentaco-ordinated 4-MeCyclam-14 complexes is acid catalyzed. The limiting rate for acid dissociation is not reached even in 2.5M HNO₃ in the case of Ni(4-MeCyclam-14)²⁺. From the formation and dissociation rates stability constants have been calculated, which do not show any macrocyclic effect.     

Electrochemical investigation of the chemical diffusion,partial ionic conductivities,and other kinetic parameters in Li3Sb and Li3Bi

The galvanostatic intermittent titration technique (GITT) has been used to electrochemically determine the chemical and component diffusion coefficients, the electrical and general lithium mobilities, the partial lithium ionic conductivity, the parabolic tarnishing rate constant, and the thermodynamic enhancement factor in “Li₃Sb” and “Li₃Bi” as a function of stoichiometry in the temperature range from 360 to 600°C. LiCl, KCl eutectic mixtures were used as molten salt electrolytes and Al, “LiAl” two-phase mixtures as solid reference and counterelectrodes. The stoichiometric range of the antimony compound is rather small, 7 × 10^?3 at 360°C, whereas the bismuth compound has a range of 0.22 (380°C), mostly on the lithium deficit side of the ideal composition. The thermodynamic enhancement factor in “Li₃Sb” depends strongly on the stoichiometry, and has a peak value of nearly 70 000; for “Li₃Bi” it rises more smoothly to a maximum of 360. The chemical diffusion coefficient for “Li₃Sb” is 2 × 10^?5 cm² sec^?1 at negative deviations from the ideal stoichiometry and increases by about an order of magnitude in the presence of excess lithium at 360°C. The corresponding value for “Li₃Bi” is 10^?4 cm² sec^?1 with high lithium deficit, and increases markedly when approaching ideal stoichiometry. The activation energies are small, 0.1–0.3 eV, depending on the stoichiometry, in both phases. The mobility of lithium in “Li₃Bi” is about 500 times greater than in “Li₃Sb” with a lithium deficit. The ionic conductivity in “Li₃Sb” increases from about 10^?4 Ω^?1 cm^?1 in the vacancy transport region to about 2 × 10^?3 where transport is probably by interstial motion at 360°C. For “Li₃Bi” a practically constant value of nearly 10^?1 Ω^?1 cm^?1 is found at 380°C. The parabolic tarnishing rate constant shows a sharp increase at higher lithium activities in “Li₃Sb” whereas in “Li₃Bi” it has a roughly linear dependence upon the logarithm of the lithium activity. The tarnishing process is about 2 orders of magnitude slower for “Li₃Sb” than for “Li₃Bi.” Because of the fast ionic transport in these mixed conducting materials, “Li₃Sb” and “Li₃Bi” may be called “fast electrodes.”     

Solvent effect on the reduction of tetravalent neptunium by metallic nickel

The feasibility of the reaction Np⁴⁺+2Ni⁰Np⁰+2Ni²⁺ in organic liquids is reported. This reaction, which is impossible to carry out in water, has been achieved in acetonitrile, while it remained impossible in dimethylformamide. This behavior in the two liquids is determined by solvent effects on the ions (Np⁴⁺, Ni²⁺) and we demonstrate that the classical Bom equation, as modified by Tanaka, is capable to foresee these different behaviors.     

Complexation of Cd2+, Ni2+, and Ag+ metal ions with 4,13-didecyl-l,7,10,16-tetraoxa-4,13-diazacyclooctadecane in acetonitrile-ethylacetate binary mixtures

Conductometric titrations have been performed in acetonitrile-ethylacetate (AN-EtOAc) binary solutions at 288, 298, 308, and 318 K to obtain the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of Cd²⁺, Ni²⁺, and Ag⁺ cations with 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (cryptand 22DD). The stability constants of the resulting 1: 1 complexes formed between the metal cations and the ligand were determined by computer fitting of the conductance-mole ratio data. There is a non-linear relationship between the logK _f values of complexes and the mole fraction of ethylacetate in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the Cd²⁺, Ni²⁺, and Ag⁺ cations with the ligand changes with the nature of the solvent. The standard enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, the complexation processes of the metal cations with the C22DD, is mainly entropy governed and the values of thermodynamic parameters are influenced by the nature and composition of the binary mixed solvent solutions.     

Orthogonally Incorporating Dual-Fluorescence Control into Gated Photochromism for Multifunctional Molecular Switching

Gated photochromism is of interest for the operation and control of modern high-tech optofunctional materials. For further advancing this topic towards the achievement of multifunctional molecular switching, however, it remains a great challenge to incorporate multiple fluorescence regulation into gated photochromism in one unimolecular system. Herein, it is reported that a dithienylethene derivative DTEN with a Schiff base connection can be facilely synthesized by one-step coupling, and it enabled distinct color and spectral changes upon different stimuli, including ultraviolet, visible light, Ni²⁺, and Al³⁺. Relying on hydrazine and hydroxy units in this molecule, compound DTEN exhibited novel Ni²⁺-locked photochromic characteristics originating from complexation of the compound with Ni²⁺ in a 2:1 stoichiometry. On the other hand, a 1:1 complexation between compound DTEN and Al³⁺ could allow both of the initial and photostationary states of DTEN to display fluorescent enhancement and a redshift, realizing a dual-fluorescence “turn-on” sensing of Al³⁺ by light. On this basis, it is argued that the switching of the coordination mode between DTEN and Ni²⁺ or Al³⁺ brings up the possibility of tunable photoswitching by multiple stimuli, which offers a novel way for future development of multifunctional switching materials with different input and output signals, as exemplified by the construction of a delicate molecular circuit.     

Morphology and composition of Ni–Co alloy powders electrodeposited from ammoniacal electrolyte

In this paper, the morphology and phase structure of Ni–Co powders electrodeposited from ammoniacal electrolyte are investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni²⁺/Co²⁺ concentration is found to influence both, the phase structure and the morphology of Ni–Co alloy powders. It is shown that the current density practically does not influence the morphology of Ni–Co alloy powders as well as alloy powder composition. At the highest ratio of the Ni²⁺/Co²⁺ ions typical spongy particles were obtained. With the decrease of the Ni²⁺/Co²⁺ ions ratio agglomerates of the size of about 100 μm, composed of a large number of fern-like dendrites on their surface were obtained. At the lowest Ni²⁺/Co²⁺ concentration ratio, among more dendritic particles, agglomerates typical for pure Co powder deposition were detected. It is also shown that depending on the Ni²⁺/Co²⁺ ratio different types of Ni and Co codeposition could be detected: anomalous and irregular. At the Ni²⁺/Co²⁺ ions ratio higher than 1 only β-Ni phase was detected, while at concentration ratios Ni²⁺/Co²⁺<1 h.c.p. α-Co phase together with β-Ni phase was detected in the alloy powder deposit.     

Solvent effect on the rate of homogeneous electron exchange of the Eu(III)-Eu(II) system in water-DMF mixtures

The kinetics of homogeneous electron exchange Eu³⁺/Eu²⁺ has been investigated in 1M HClO₄, water+dimethylformamide (DMF) mixed solvent by using labeled europium. Non-monotonic variations of the electron exchange rate constants as a function of the solvent composition was observed.     

Investigating the effect of mono‐ and multivalent counterions on the conformation of poly(styrenesulfonic acid) by nanopores

Polyelectrolytes are useful materials that have many technical, medical, physiological and biological applications. The properties of polyelectrolytes are determined not only by their chemical composition but also by their conformational states. However, the conformations of polyelectrolytes in solution are very difficult to characterize. Herein, we propose to use a protein nanopore to investigate the effect of mono‐ and multivalent counterions on the conformational changes of a simple polyelectrolyte, sodium poly(styrenesulfonic acid) (NaPSS). High concentration of KCl induced a conformational transition of NaPSS from “swollen random coil” form in low salt concentration to “random coil” form and was evidenced by the changes of the translocation event pattern. Addition of Mg²⁺ in buffer solution did not cause notable changes of NaPSS translocation events, but Dy³⁺ and Y³⁺ were shown to have remarkable effects on the translocation profile of NaPSS. Bridging events caused by Dy³⁺ or Y³⁺ between polyelectrolyte chains largely affected current blockage and dwell time of the translocation events. Our results provide experimental evidence for the classical theories of conformational transitions of polyelectrolytes and may find applications in many other polyelectrolyte‐related researches.