The heat effects of formation of Co2+ ion complexes with carboxylic acids

The heat effects of complex formation between cobalt(II) ions and malonic, maleic, and succinic acids were measured on an isothermic-shell calorimeter at 298.15 K and several ionic strength values against the background of NaNO₃. The standard thermodynamic characteristics of complex formation in aqueous solution were calculated.     

The thermodynamic parameters of complex formation between the copper(II) Ion and β-alanine in aqueous solution

The heats of formation of β-alanine complexes with the doubly charged copper(II) ion were determined calorimetrically. The heat effects of interaction of a solution of the amino acid with a solution of copper(II) were measured at 288.15, 298.15, and 308.15 K and ionic strengths of 0.50, 0.75, and 1.00 against the background of KNO₃. The heats of dilution of a solution of copper nitrate with solutions of the background electrolyte were also determined for the introduction of the corresponding corrections. The standard thermodynamic characteristics of complex formation were calculated. The influence of temperature on the thermal effects of complex formation in the β-alanine-copper(II) ions system were considered. The standard enthalpies of formation of CuAla⁺ and CuAla₂ complex particles in aqueous solution were calculated.     

The thermodynamic characteristics of complex formation between calcium ions and L-leucine in aqueous solution

Complex formation of L-leucine with calcium ions in aqueous solution was studied by potentiometric titration at 298.15 K and ionic strength values I = 0.5, 1.0, and 1.5 (KNO₃). The formation of the CaL⁺ and CaHL²⁺ complex particles was established and their stability constants were determined. The enthalpies of protolytic equilibria of leucine and formation of calcium ion complexes with leucine were determined calorimetrically at 298.15 K and I = 0.5 (KNO₃). The thermodynamic characteristics of complex formation between calcium ions and L-leucine were calculated.     

Thermodynamic characteristics of formation reactions of Zn<Superscript>2+</Superscript> and Ni<Superscript>2+</Superscript> complexes with succinic acid in aqueous solutions

The heat effects of complex formation between zinc(II) and nickel(II) ions and succinic acid were determined calorimetrically at 298.15 K and several ionic strength values against the background of NaNO₃. The standard thermodynamic characteristics of complex formation in aqueous solution were calculated.     

Study on the equilibria of the complex formation of molybdenum(VI) with 3,5-dinitrocatehol and 3-(2-naphthyl)-2,5-diphenyl-2H-tetrazolium chloride

The formation of an ion-associated complex between the anionic chelate of Mo(VI)–3,5-dinitrocatehol (3,5-DNC) and the cation of 3-(2-naphthyl)-2,5-diphenyl-2H-tetrazolium chloride (TV) in the liquid–liquid extraction system Mo(VI)–3,5-DNC–TV–H₂O–CHCl₃ was studied by spectrophotometry. The optimum conditions for the complex formation and extraction of the ion-associated complex were established. The effect of co-existing ions and reagents on the process of complex formation was investigated under optimum extraction conditions. The validity of Beer’s law was checked and some analytical characteristics were calculated. The association process in aqueous phase and the extraction equilibria were investigated and quantitatively characterized. The following key constants of the processes were calculated: association constant, distribution constant, extraction constant and recovery factor. The molar ratio of the reagents was determined by independent methods. Based on this, a reaction scheme, a general formula and a structure of the complex were suggested.     

Photoelectron spectra of electron donor—acceptor complexes between bromine and alkylamines

The photoelectron spectra of N,N-diethylmethylamine—Br₂, triethylamine—Br₂, tri-n-propylamine—Br₂ and tri-n-butylamine— Br₂ complexes were observed. The n orbitals of the alkylamines as electron donors were found to be stabilized by molecular complex formation, while the σ4p and π4p orbitals of the bromine molecule were destabilized. These results strongly support the charge-transfer mechanism for the complex formation.     

Synthesis,stepwise instability constants and oxidation of bis-[bromazepan]CuI perchlorate by molecular oxygen in dimethyl sulphoxide

Summary The oxidation with molecular oxygen of the cuprous salt, Cu(MeCN)₄ClO₄, and of bis(bromazepan)Cu^I perchlorate complex in the presence of different concentrations of the complexing agent bromazepan in DMSO was studied and the formation constants of the complex were calculated from the kinetic data. For comparative purposes the formation constants were also determined spectrophotometrically.     

Kinetics and Mechanism of Oxidation of Hydroquinone by Tetrabutylammonium Tribromide Ion in Aqueous Acetic Acid

The oxidation of hydroquinone by environmentally benign tetrabutyl ammonium tribromide (TBATB) was carried out in 50% V/V aqueous acetic acid medium under pseudo-first-order conditions, keeping a large excess of hydroquinone over the oxidant. The main reactive species of oxidant and substrate were found to be the Br₃^-\mathrm{Br}_{3}^{-} ion and hydroquinone, respectively. The reaction proceeds with prior complex formation between the reactants followed by its slow decomposition to generate semiquinone and bromine radicals. The complex formation was kinetically verified by its Michaelis–Menten plot. The solvent effect was verified by using Grunwald–Winstein equation which is consistent with an S_N2 mechanism. The formation constants for the complex and rate constant for the slow decomposition step were determined by studying the reaction at five different temperatures. The values of formation constant of the complex and the rate constant for its decomposition were determined at these temperatures. The activation parameters with respect to the slow step of the reaction have also been determined.     

Hydrogen bond energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex formation

The formation energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex were measured in C₆D₆ solution by ¹H-NMR spectroscopy and values of 25.1 and 44.6 kJ/mol were obtained. The former value is about twice the magnitude of hydrogen bond energies which are generally observed for the N---HN system, and latter value is about half the sum of the formation energies of the 2-aminopyridine and 2-pyridone dimers. The formation energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex were calculated by the CNDO/2 method, and their formation energies (−ΔH) were estimated to be 28.5 and 42.8 kJ/mol, respectively.     

The enthalpies of formation of copper(II) complexes with nicotinamide in aqueous ethanol and DMSO

The enthalpies of complex formation between nicotinamide and copper(II) perchlorate in aqueous ethanol and dimethylsulfoxide (DMSO) were determined calorimetrically. The maximum exothermic effect was observed in a solvent with ～0.1 mole fractions of DMSO. The exothermic effect of complex formation increased as the concentration of ethanol grew. The role played by solvation in the thermodynamic characteristics of monoligand complex formation was considered. The influence of solvent composition on Δ_r H ^o was largely related to the resolvation of the ligand donor atom.     

1H NMR and calorimetric study on binding ability of cyclodextrins to isomeric pyridinecarboxylic acids in aqueous solution

Complex formation of α- and β-cyclodextrins with isomeric pyridinecarboxylic acids (picolinic, nicotinic and isonicotinic acids) in water were studied by calorimetry and ¹H NMR at 298.15 K. The obtained results revealed the weak 1:1 complex formation governed by the cavity dimensions and position of the carboxylic group in the pyridine ring. It was found that selective inclusion complex formation of α- and β-cyclodextrins with nicotinic and isonicotinic acids takes place. In the case of picolinic acid, the considerable role of external interactions and formation of less stable complexes were detected. The location of the carboxylic group in the meta-position of pyridine ring is more favorable for the effective binding. The pyridinecarboxylic acids are shallow inserted into α-cyclodextrin cavity possessing the smaller diameter, while they are deeply included into β-cyclodextrin cavity. Thermodynamic parameters of complex formation (K, Δ_cG⁰, Δ_cH⁰ and Δ_cS⁰) were calculated and discussed in terms of influence of reagents structure.     

Effect on the Solubility,Wettability, and Dispersibility of the β‐CD‐Deltamethrin Inclusion Complex in Presence of Mixed Surfactant (C14MEA/AOS) Blend

An inclusion complex formation using β‐cyclodextrin (β‐CD) as the host molecule and deltamethrin as guest molecule was a first step towards improvement in conventional insecticide formulations. β‐CD‐deltamethrin inclusion complex formation in the absence and presence of the nonionic myrisitic acid monoethanolamide (C₁₄MEA)/anionic α‐olefin sulfonate C₁₂‐C₁₄ (AOS) mixed surfactant system was comparatively studied. The co‐evaporation method was used for complex formation, which was subsequently characterized by analytical methods such as FTIR and XRD techniques. Important physical properties such as solubility, dispersion stability, and wettability were also studied.     

Effect of 4f-shell excitation of Eu(fod)3 on its complex formation with alicyclic ketones

The complex formation of alicyclic ketones, viz., camphor, cyclohexanone, menthone, and cytisine, with the Eu(fod)₃ chelate (fod is 7,7-dimethyl-1,1,1,2,2,3,3-heptafluorooctane-4,5-dione) in the ground and excited states was studied by chemiluminescence and kinetic luminescence spectroscopy, respectively. The stability constants and thermodynamic parameters of complex formation were determined. An increase in the stability of the electron-excited complexes [Eu(fod)₃*·Ketone] is explained by the enhancement of the acceptor ability of the Eu³⁺ chelate due to an increase in the fraction of the covalent component caused by the involvement of 4f-orbitals. The results obtained give direct evidence for the effect of the 4f-shell excitation of Eu(fod)₃ on complex formation due to the involvement of f-electrons in the chemical bonds.     

Theoretical investigation of the electrophilic attack. IX. Ab initio study of the C2H4 · HF molecular complex

Several configurations of the C₂H₄ · HF molecular complex were studied using the 4–31G basis set. The most stable configuration was found to be the π hydrogen bonded complex. For this structure the interaction energy was computed employing a double-zeta basis plus polarization functions. The changes in electronic properties of the components C₂H₄ and HF due to complex formation were discussed.     

Formation of an η-allyl and a cyclic γ-hydroxyalkyl complex of molybdenum from reaction of MoH2(η-cyclopentadienyl)2 with homoallyl alcohol

The reaction of Cp₂MoH₂ (Cp=η⁵-C₅H₅) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η³-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η³-crotyl complex.     

The thermodynamic characteristics of formation of Zn<Superscript>2+</Superscript> complexes with D,L-tryptophan in aqueous solution

The heat effects of formation of D,L-tryptophan complexes with doubly charged zinc ions were determined calorimetrically. The heat effects of interaction of amino acid solutions with a solution of Zn(II) were measured at 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 against the background of KNO₃. The heats of dilution of solutions of zinc nitrate with solutions of the background electrolyte were determined under the same conditions. The corresponding corrections were introduced. The thermochemical data were processed taking into account step equilibria. Along with complex formation, “side” protolytic processes were included. The standard thermodynamic characteristics of complex formation were calculated. The influence of temperature on the heat effects of complex formation in the β-alanine-zinc(II) ions system was considered.     

Molecular and supramolecular structures of complexes formed by polyelectrolyte‐surfactant interactions: effects of charge density and compositions

The process of complex formation and the structure of the complexes were studied for the surfactant binding of the N‐alkylpyridinium chlorides (C_nPyCl, n = 12, 16) to the sodium salt of poly(styrenesulfonate) (NaPS) and its copolymer with styrene. Both the NaPS and the amphiphilic copolymer form non‐stoichiometric complexes with an excess of the cationic surfactants. The NaPS‐complex with pronounced short‐range (d₁) and long‐range (d₂) orderings is insoluble, and the amphiphilic copolymer‐complex is water‐soluble when bound with extra charges. The mechanism of the complex formation was discussed in terms of the charge density and chemical composition of the polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 635–644, 1999     

Catalytic Ammonia Synthesis Mediated by Molybdenum Complexes with PN3P Pincer Ligands: Influence of P/N Substituents and Molecular Mechanism

Three molybdenum trihalogenido complexes supported by different PN³P pincer ligands were synthesized and investigated regarding their activity towards catalytic N₂-to-NH₃ conversion. The highest yields were obtained with the H-PN³P^tBu ligand. The corresponding Mo(V)-nitrido complex also shows good catalytic activity. Experiments regarding the formation of the analogous Mo(IV)-nitrido complex lead to the conclusion that the mechanism of catalytic ammonia formation mediated by the title systems does not involve N-N cleavage of a dinuclear Mo-dinitrogen complex, but follows the classic Chatt cycle.     

Carbon-13 NMR spectroscopy of acrylic monomer and Lewis acid complexes

¹³C NMR spectra of acrylic monomers complexed with a Lewis acid were measured and their electronic structures discussed in relation to their alternating copolymerizability. The β-carbon of acrylonitrile and methacrylonitrile showed a downfield shift due to the complex formation with the Lewis acid, while the α-carbon showed an upfield shift and the nitrile carbon showed no significant shift. The degree of shift of olefinic carbons decreased in the following order: AlCl₃ > EtAlCl₂ > Et_1.5AlCl_1.5 > Et₂AlCl > SnCl₄, EtOAlCl₂ > Et(EtO)AlCl, which seems to run parallel to the Lewis acidity and acid strength. On the other hand, the chemical shift of olefinic carbons of methyl acrylate, methyl methacrylate, and olefinic diesters was influenced little by complex formation with Lewis acids, whereas the carbonyl and alkoxyl carbons were deshielded significantly by the complex formation. These results are discussed in terms of electron distribution on the carbons and an alternating polymerization mechanism.     

Theoretical study of donor-acceptor ability of borazine,alumazine, and boraphosphinine

Donor-acceptor complexes of borazine, alumazine, and boraphosphinine were studied by a quantum-chemical method. Structural and thermodynamic characteristics of complexes with Lewis acids (BCl₃ and AlCl₃) and bases (NH3 and pyridine Py) were calculated by the B3LYP method with the TZVP basis set. Energies of donor-acceptor bonds and energies of reorganization of donors, acceptors, and heterocycles upon the complex formation were found. Analysis of the energy variations occurring at the complex formation has shown that the reorganization energies of acceptors (BCl₃ and AlCl₃) and heterocycles play a key role in the complex stabilizations, whereas the reorganization energies of donors (NH₃ and Py) are small and do not bring essential contribution to the complex-formation energy. The stability of donor-acceptor complexes decreases in the sequence alumazine > boraphosphinine > borazine. High alumazine reactivity toward chlorine atoms of the acceptor molecules BCl₃ and AlCl₃ was noted.