Values Of Formation Constants Research Articles

Syntheses and Properties of Cycloamidines Based on 4H-Imidazoles

Employing three different syntheses a broad spectrum of 4H-imidazoles 3a - 3s has been synthesized. In the course of the two-fold aminolysis reaction leading to derivatives 3q - 3s, deeply colored byproducts could be isolated and structural characterized.These novel donor-acceptor derivatives of type 7 consist of an 1H- and 4H-imidazole which are connected by a nitrogen bridge and rearrange via rapid 1,3-/1,5-hydride shifts. Using 1H NMR experiments the aminolysis product 3p shows prototropic isomers which could be detected in equilibrium for the first time. Cyclovoltammetric measurements of a series of substituted 2-aryl derivatives 3d - 3i displayed two reversible single electron transfer steps with relatively small semiquinone formation constants between 102 and 4×103. The 4H-imidazole 3d was successfully converted into boratetraaza-pentalene 8a, which showed two well separated reduction potentials. The value of semiquinone formation constant of 8a (1.8×1015) is even higher than those reported for similar derivatives. 4H-imidazoles can also be employed for the efficient complexation of catalytically important metals as exemplified by copper complexes 11 and 12. Derivative 3m, which possesses an additional chelating pyridine substructure, formed a stable complex of structural composition Zn(3m)2 with diethyl zinc

Experimental and Theoretical Study on the Inclusion Capability of a Fluorescent Indolizine β-Cyclodextrin Sensor Towards Volatile and Semi-volatile Organic Guest

Inclusion equilibria of a new fluorescent indolizine modified β-cyclodextrin were studied in aqueous solution to evaluate its use as a fluorescent chemo-sensor for volatile organic compounds (VOCs). The host compound shows a decrease of the fluorescence intensity by adding adamantanol, benzene, toluene, phenol and p-cresol as guest. The sensing parameter (ΔI/I0) was used to show the sensing ability of the host. The formation constant values measured using a spectral displacement method and a specific algorithm treatment are reported. Although the guest binding ability of the sensor is not enhanced by the existence of the hydrophobic cap, this new cyclodextrin sensor shows a very strong sensing ability. The experimental values of the constants were in good agreement with the computed complexation energies, ΔE, from molecular mechanics modelling of the inclusion process.

Solvent effects on hydrogen bonding between 1-pentanol and butyl methacrylate

The hydrogen bonding between 1-pentanol and butyl methacrylate (BMA) was investigated in n-heptane, CCl4, and benzene as solvents by using FTIR spectroscopic method. Utilizing Nash method the formation constant and free energy change of 1 : 1 complexes has been determined. The results show a significant dependence of the association constant upon the solvents used. The solvent effect on the formation of hydrogen bond equilibria is discussed in terms of specific interaction between the solute and the solvent. The variation of formation constant values with the solvents confirm the solvent environment which may affect the strength of intermolecular hydrogen bond formation between free O–H group of 1-pentanol and the carbonyl group of BMA (O–H···O=C).

Speciation of Phytate Ion in Aqueous Solution. Sequestering Ability toward Mercury(II) Cation in NaClaq at Different Ionic Strengths

As a contribution to understanding the speciation of mercury in the environment and to the study of the sequestering ability of phytate (Phy) toward heavy metal and organometal cations, this paper describes the results of an investigation (at t = 25 degrees C by potentiometry, ISE-H+ glass electrode) of its interactions with mercury(II) cation in NaCl aqueous solutions at different ionic strengths (I = 0.15 and 1.0 mol L(-1)), in the pH range 2.5 < or = pH < or = 9.5 and considering metal-to-ligand ratios of 1:1 < or = Hg/Phy < or = 4:1. The formation of 11 HgiHjPhy(12-2i-j)(- species with i = 1 and 0 < or = j < or = 7 and i = 2 and 0 < or = j < or = 2 was observed. Their complex formation constant values proved to be fairly dependent on ionic strength. The speciation of phytic acid and mercury(II) is also dependent on the metal-to-ligand ratio; the dependence of the stability of phytate-mercury(II) species on the phytate protonation step was modeled, and an empirical predictive relationship was proposed. From the results obtained, phytate has very good sequestering ability toward Hg2+, even in the presence of considerable excesses of chloride ion, that is, another ligand strongly interacting with mercury; this supports future studies both on the use of plants that naturally synthesize it for phytoremediation purposes and on its direct application in remediation techniques.

Spectral properties of new N, N′-bis-alkyl-1,4,6,8-naphthalenediimide complexes

The photophysical properties of two N, N′-bis-alkyl-1,4,6,8-naphthalenediimide (DCN1 and DCN2) have been studied in chloroform and N, N-dimethylformamide solvents. The ability of DCN2 in N, N-dimethylformamide to detect metal cations have been monitored by the fluorescence emission spectroscopy. It has been shown that the fluorescent intensity is very sensitive to the concentration of Fe 3+ cations. The reaction of iodine with N, N′-bis-alkyl-1,4,6,8-naphthalenediimide in chloroform solution have been investigated by spectrophotometric method. The results indicate the formation of two CT-complexes [(DCN1)I] +·I 3 − and [(DCN2)I] +·I 3 − at donor:acceptor molar ratio of 1:2. The [(DCN1)I] +·I 3 − shows the characteristic absorptions of I 3 − ion at 290 and 360 nm while the charge-transfer transition of [(DCN2)I] +·I 3 − occurs at 310 nm. Three characteristic bands at the far infrared region in each iodine complex are observed around 135, 105 and 85 cm −1 due to ν as (I–I), ν s (I–I) and δ (I 3 −), respectively with C 2v symmetry. The values of the complex formation constant, K, and the absorptivity, ɛ have been calculated.

Complex formation of some transition metals with thiazole Schiff bases

Proton-ligand stability constants of five Schiff bases, derived from 4-(p-bromophenyl)-2-aminothiazole and R substituted salicylaldehyde (R = H, 5-CH 3 , 4-CH 3 and 5-Br) or 2-hydroxy-l-naphthaldehyde, and formation constants of their transition metal (Co, Ni, Cu and Zn) complexes have been determined pH-metrically at room temperature (25 °C) and at constant ionic strength, 1 = 0.1 M (NaClO 4 ), in 75: 25% (v/v) ethanol-water medium using Calvin-Bjerrum pH-technique as adopted by Irving-Rossotti. The order of stability constants of the complexes has been proposed, which is in accordance with the order suggested by Irving-Williams. The effect of elevated temperature (35 °C and 45 °C) on the determination of formation constants of metal complexes has been studied. Decrease in value of formation constant of the complex with increase in temperature indicates that low temperature is favorable for complex formation. The thermodynamic parameters (AG, ΔH and AS) at different temperatures have been calculated.

Studies on some ternary complexes of CuII with diamines and hydroxy acid

Solution studies on ternary complexes of Cu II with diamines (A) viz. ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, o-, m- or p-phenylenediamine and salicylic acid (H 2 L) in the ratio of 1: 1: 1 have been investigated by pH metric technique at μ = 0.2 M (NaClO 4 ) and at temperature 30 ± 0.1 °C in aqueous media. The formation constant values for ternary system Cu II -diamine-salicylic acid has been calculated and probable species like H 2 L, HL, CuALH, CuAL 2 etc. are pruned with FORTRAN IV computer program. These values are discussed in terms of basicity of primary and secondary ligand, size of chelate ring, A log K T values and different statistical factors such as metal-ligand interaction, structure of ligands and intermolecular ligand-ligand interactions. Structure of complexes is suggested on the basis of molecular modeling.

Electronic structures and ionicity in [60]fullerene/polycyclic aromatic hydrocarbon charge transfer complexes studied by UV–Vis and NMR spectroscopic techniques

A detailed UV–Vis spectrophotometric, thermodynamic and NMR studies have been carried out to look insight into the nature of molecular interactions of the electron donor–acceptor complexes of [60]fullerene with three different polycyclic aromatic hydrocarbon (PAH) molecules in CCl 4 medium. Well defined charge transfer (CT) absorption bands have been located in the visible region. We extract degrees of charge transfer, oscillator and transition dipole strengths by analyzing the transition energy of the CT band as a function of vertical ionization potentials of the donors studied. The influences of the PAH on the absorption spectrum of [60]fullerene are studied. The experimental results have been explained using a theoretical model that takes into account the interaction between electronic subsystems of PAH with [60]fullerene. Formation constants ( K) of the [60]fullerene/PAH complexes are determined spectrophotometrically (utilizing Benesi–Hildebrand equation) at four different temperatures and by 1H NMR spectroscopic technique. Trend in the formation constant values for the [60]fullerene/PAH complexes are discussed in terms of enthalpies and entropies of formation. Free energies of formation values for the [60]fullerene/PAH systems as well as ab initio calculation suggest that nature of substitution and steric effect in the PAH systems play vital role in formation of EDA complexes with [60]fullerene.

Solvent Effects on Hydrogen Bonding between Ethyl Methacrylate and 1-Butanol

The hydrogen bonding between ethyl methacrylate dissolved in 1-butanol in inert solvents viz., n-heptane, carbon tetrachloride and benzene has been studied using FTIR spectroscopy. Utilizing Nash method the formation constant of the 1:1 complexes has been calculated. The formation constant and free energy change values vary with the solvents are observed in the present study confirms the solvent environment may affect the strength of intermolecular hydrogen bond formation between free hydroxyl group of 1-butanol and the carbonyl group of ethyl methacrylate.

Additivity Factors in the Binding of the Diethyltin(IV) Cation by Ligands Containing Amino and Carboxylic Groups at Different Ionic Strengths

Complex formation constants were determined potentiometrically (by a ISE-H+, glass electrode) in the systems, M2+ – Lz – H+ [M2+ = (C2H5)2Sn2+, Lz = malonate, glycinate and ethylenediamine] at t = 25 ∘C and 0.1 mol-L−1≤ I/ ≤ 1 mol-L−1 in NaClaq (0.1 mol-L−1 ≤ I ≤ 0.75 mol-L−1 for the ethylenediamine system). Thermodynamic values of formation constants, at infinite dilution, are [± 95% confidence interval, Tβpqr refer to the equilibrium, pM2+ + qLz + rH+ = M p L q H r (2+ z + r )]: for malonate, log10 Tβ110 = (5.47 ± 0.10); for glycinate, log10 Tβ110 = (9.54 ± 0.08), log10 Tβ111 = (12.97 ± 0.10); and for ethylenediamine, log10 Tβ110 = (10.47 ± 0.10), log10 Tβ120 = (16.17 ± 0.12) and log10 Tβ111 = (15.46 ± 0.10). The dependence on ionic strength of the formation constants was modeled by a simple Debye–Huckel type equation and by the SIT approach. By analyzing the stability of the species in the three different systems we found a simple additivity rule that can be expressed by the relationship: log10 K = 6.46 nN + 3.96 nO − 0.60 (nN2+ nO2), with a mean deviation, e(log10 K) = 0.15 (K = equilibrium constant for the interaction of the organometal cation with the unprotonated or protonated ligand, nN = number of amino groups and nO = number of carboxylic groups of the ligand(s) involved in the formation reaction of complex species).

Absorption spectrophotometric study of supramolecular complexation of [60]- and [70]fullerenes with 24,26-dimethoxy-25,27-dihydroxy calix[4]arene

Supramolecular interactions of 24,26-dimethoxy-25,27-dihydroxy calix[4]arene (1) with [60]- and [70]fullerenes have been studied in only chloroform and in a ternary solvent mixture comprising of chloroform, ethyl alcohol and toluene by UV–vis absorption spectrophotometric method. The experimental results are explained using the model that takes into account the interaction between electronic subsystems of 1 and fullerene. The most interesting feature is the preference of [60]fullerene over [70]fullerene for 1 in ternary solvent mixture as revealed by higher value of formation constant of [60]fullerene/1 complex. The selectivity towards [60]fullerene opens up the way toward self-assembling systems and new separation and purification methods for fullerenes.

Equilibrium Studies of Schiff Bases and Their Complexes with Ni(II), Cu(II) and Zn(II) derived from Salicylaldehyde and Some α-Amino Acids

The acid-base equilibria of Schiff bases derived from salicylaldehyde, glycine, alanine, serine, tyrosine, and phenylalanine, and their Ni(II), Cu(II) and Zn(II) complex formation equilibria were investigated by a potentiometric method in aqueous solution (t = 25∘C, μ = 0.1 M, KCl). The data from the potentiometric titrations were evaluated by means of the BEST computer program. The order of the formation constant values of the Schiff bases was Sal-Ala > Sal-Gly > Sal-Ser > Sal-Phe > Sal-Tyr, which is the same order as the increasing log K1 values of amino acids (and the log K2 values of tyrosine) with the exception of an inversion between serine and phenylalanine. Also, it was seen that the stability constants, log β1 and log β2, of Schiff base–metal complexes vary for all the metal ions investigated, viz., Sal-Gly > Sal-Ala > Sal-Ser > Sal-Tyr > Sal-Phe with the exception of Sal-Gly in the copper complex. The effect of the nature of the amino acids on their formation, protonation and stability constants was also discussed.

Speciation of phytate ion in aqueous solution. Dimethyltin(IV) interactions in NaCl aq at different ionic strengths

As the introduction of a systematic study on the sequestering ability of phytate (Phy) towards heavy metal and organometal cations, this paper describes the results of an investigation (at t = 25 °C by potentiometry, ISE-H + glass electrode) of its interactions with dimethyltin(IV) cation [(CH 3) 2Sn 2+, DMT] in NaCl aqueous solutions at different ionic strengths (0.1 ≤ I (mol L −1) ≤ 1), in the pH range 2.5 ≤ pH ≤ 8.5 and considering metal to ligand ratios 1:1 ≤ DMT:Phy ≤ 4:1. We observed the formation of 18 DMT i H j Phy (12−2 i− j)− species: with i = 1 and 0 ≤ j ≤ 7; i = 2 and 0 ≤ j ≤ 5; i = 3 and 0 ≤ j ≤ 3. Their complex formation constant values are fairly dependent on ionic strength and this dependence was modeled by a Debye-Hückel type equation. The speciation of phytic acid and dimethyltin(IV) is also dependent on the metal to ligand ratio; the dependence of the stability of phytate-dimethyltin(IV) species on both the phytate protonation step and the number of cations bound to the ligand has been modeled and an empirical predictive relationship is also proposed. From the results obtained it emerged that phytate has very good sequestering ability towards (CH 3) 2Sn 2+. Comparisons are made with other ligands, such as ethylenediamine- N, N, N′, N′-tetraacetic acid (EDTA) and phosphate.

Solubility of (UO2)3(PO4)2⋅4H2O in H+-Na+-OH−-H2PO−4-HPO2−4-PO3−4-H2O and Its Comparison to the Analogous PuO2 +2 System

The objectives of this study were to address uncertainties in the solubility product of (UO2)3(PO4)2⋅4H2O(c) and in the phosphate complexes of U(VI), and more importantly to develop needed thermodynamic data for the Pu(VI)-phosphate system in order to ascertain the extent to which U(VI) and Pu(VI) behave in an analogous fashion. Thus studies were conducted on (UO2)3(PO4)2⋅4H2O(c) and (PuO2)3(PO4)2⋅4H2O(am) solubilities for long-equilibration periods (up to 870 days) in a wide range of pH values (2.5 to 10.5) at fixed phosphate concentrations of 0.001 and 0.01 M, and in a range of phosphate concentrations (0.0001–1.0 M) at fixed pH values of about 3.5. A combination of techniques (XRD, DTA/TG, XAS, and thermodynamic analyses) was used to characterize the reaction products. The U(VI)-phosphate data for the most part agree closely with thermodynamic data presented in Guillaumont et al.,(1) although we cannot verify the existence of several U(VI) hydrolyses and phosphate species and we find the reported value for formation constant of UO2PO−4 is in error by more than two orders of magnitude. A comprehensive thermodynamic model for (PuO2)3(PO4)2⋅4H2O(am) solubility in the H+-Na+-OH−-Cl−-H2PO−4-HPO2−4-PO3−4-H2O system, previously unavailable, is presented and the data shows that the U(VI)-phosphate system is an excellent analog for the Pu(VI)-phosphate system.

π-electronic charge-transfer interactions in supramolecular complex formation between fullerenes and 5,10,15,20-tetrahexylporphyrin

UV–Vis spectral investigations on fullerenes/5,10,15,20-tetrahexylporphyrin (TP) supramolecular complexes are reported in CCl 4 and CHCl 3. An absorption band due to charge transfer (CT) transition is observed in the visible region. Vertical ionization potential of TP was determined from the CT transition energy. CT is very weak in these complexes as reflected from very low values of oscillator strengths and transition dipole strengths. All of the complexes are found to be stable with 1:1 stoichiometry. Thermodynamic parameters for the supramolecular complexes of TP with [60]- and [70]fullerenes are reported. The high formation constant value for the [60]fullerene/TP complex as compared to [70]fullerene/TP complex indicates selectivity of TP molecule towards [60]fullerene.

Microspectrophotometric determination of thorium(IV) and uranium(VI) with methylthymol blue

Attempts have been made to improve the sensitivity of complexation reactions of Th I V and U V I with methylthymol blue (MTB) in presence of cationic surfactant cetyldimethylethylammonium bromide (CDEAB). The marked bathochromic shift in λ m a x , considerable increase in sensitivity and extreme stability of these ternary complexes in presence of CDEAB were found to be useful in microdetermination of metal ions under study. The composition and values of conditional formation constants have been evaluated in presence of CDEAB and various analytical parameters, viz. conformity to Beer's law, photometric ranges, Sandell's sensitivity and molar absorptivity have been studied.

Determination of Microscopic Equilibrium Constants for the Complexation of Ditopic Guests by Cyclodextrins from NMR Experiments

The complexation of 3-[(3-cholamidopropyl)dimethylammonio]-l-propanesulfonate (CHAPS) by β- and γ-cyclodextrin (β- and γ-CD) has been studied by using 1D- and 2D-NMR techniques. For the CHAPS/β-CD system both 13C and 1H NMR spectra exhibit split lines consistent with slow exchange rate between one or more complexes and free species. Job's plots suggest that complexes with 1:1 stoichiometry are formed. However, ROESY experiments suggest that β-CD is complexing the steroid nucleus at two sites, the first one being mainly the side chain of the guest, and the second one being the A/B rings. The conclusion is that two isomeric 1:1 complexes, and , are obtained. The concentrations of free and complexed species were measured from the integration of 1H NMR signals, allowing an independent determination of the two microscopic equilibrium constants, and , associated with the formation of the two isomeric complexes, and the macroscopic equilibrium constant, K11 (= + ). A good agreement between the values obtained is observed. The slow exchange rate for the formation and decomposition of the complex is understood as a barrier penetration problem for the side chain to cross through the cyclodextrin cavity since the methyl groups linked to the charged nitrogen atom of the side chain are bulky enough to force a large distortion of the β-CD during the penetration. However, the origin of the energy barrier for the complexation of the wide end of the steroid nucleus leading to a slow exchange regime is unknown. The travelling of the CHAPS side chain through a larger cyclodextrin cavity should be faster. Therefore, complexation studies between CHAPS and γ-CD were undertaken. Now, only one type of complex was observed and the fast limited exchange was obeyed. The value for the equilibrium formation constant was obtained from the analysis of the chemical shift displacements of carbon atoms of γ-CD with increasing CHAPS concentration. ROESY experiments suggest that the side chain is unfolded outside the cyclodextrin cavity forming a rotaxane-type structure.

Binary Complexes of Zirconium(IV) Naphthylideneamino Acids and their Ternary Complexes with Some Imidazoles. Synthesis, Characterization, and Electrochemical Studies

A new series of binary and ternary complexes of zirconium(IV) with N‐naphthylideneamino acids and some imidazoles has been synthesized. The complexes were characterized on the basis of elemental analyses, 1H NMR, IR and electronic spectra, conductivity, and thermal analytical data. It was found that N‐naphthylideneamino acids act as divalent tridentate (ONO) Schiff bases, whereas the imidazoles behave as monodentate ligands. The involvement of anions (OAc− and Cl−) in coordination was explored. The apparent formation constant values of Zr(IV)–Schiff base binary complexes were determined by a continous‐variation spectrophotometric method. Voltammetric results indicate that some of the prepared complexes underwent two successive, irreversible and reversible one‐electron charge transfer steps coupled with a follow‐up chemical reaction. The stability and redox properties of complexes are discussed in relation to the ligand molecular structure.

Reflections on the calculation and publication of potentiometrically-determined formation constants

Calculation and reporting procedures are described, which aim to improve the quality and comparability of published formation constant values obtained by glass-electrode potentiometry. Ways in which the processing of data by computer optimization programs can be standardized are the main concern, particularly in respect of improving the usefulness of equilibrium data through incorporation into large publically available databases. These recommendations may be particularly valuable to researchers beginning in this field as well as to those who determine formation constants only occasionally.

Studies on Charge-Transfer Complexes of 2,3-Dicyano-1,4-naphthoquinone with Some Ring and N-Substituted Anilines

The charge-transfer complexes (CT-complexes) between 2,3-dicyano-1,4-naphthoquinone (DCNQ) and some aromatic anilines, both ring and N-substituted, were studied spectrophotometrically in three chlorinated solvents, viz. chloroform, dichloromethane, and 1,2-dichloroethane at different temperatures. All the donors are known to form stable 1:1 stoichiometric complexes with DCNQ and their stoichiometry was unaffected by the variation of temperature over the studied range. The change in polarity of the solvent also doesn’t affect the stoichiometry of the complexes. The determined formation constant values are in the range of 0.49–10.8 dm3 mol−1, the highest is for the N-benzylaniline and the lowest is for o-chloroaniline. The effect of functional groups on the aniline moiety towards the strength and its electron releasing property has been discussed. The ΔH, ΔS, and ΔG values are all negative, so the studied complexes are reasonably stable and exothermic in nature. The ionization potentials of the donors were determined using the charge-transfer (CT) absorption bands of the complexes. The dissociation energies (W) of the charge-transfer excited state for the CT-complexes were also determined and are found to be constant.