Mole Ratio Data Research Articles

Study of Complex Formation of Dibenzo-18-Crown-6 with Ce3+, Y3+, $\mathrm{UO}_{2}^{2 +}$ and Sr2+ Cations in Acetonitrile–Dioxane Binary Solvent Mixtures

The complexation reactions of dibenzo-18-crown-6 (DB18C6) with Ce3+, Y3+, \(\mathrm{UO}_{2}^{2 +}\) and Sr2+ cations were studied in acetonitrile–dioxane (AN–dioxane) binary solvent solutions at different temperatures by the conductometric method. The stability constants of the resulting 1:1 complexes were determined from computer fitting of the conductance–mole ratio data. The results show that dibenzo-18-crown-6 does not exhibit selectivity for the cation whose ionic size is closest to the cavity size of this macrocyclic ligand in AN–dioxane binary solvent solutions. A nonlinear relationship was observed between the stability constants (log 10Kf) of these complexes with the composition of the AN–dioxane binary solvent. Values of thermodynamic parameters (\(\Delta H_{\mathrm{c}}^{\circ}, \Delta S_{\mathrm{c}}^{\circ}\)) for complexation reactions were obtained from the temperature dependence of the stability constants. The results show that the values along with the sign of these parameters are influenced by the nature and composition of the mixed solvent.

133Cs NMR Study of Cs+ Ion Complexes with Aza-18-crown-6, Diaza-18-crown-6 and Dibenzyldiaza-18-crown-6 in Binary Acetonitrile–Nitromethane Mixtures

Cesium-133 nuclear magnetic resonance spectroscopy was used as a sensitive probe to investigate the stoichiometry and stability of Cs+ ion complexes with aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6) and dibenzylediaza-18-crown-6 (DBzDA18C6) in different binary acetonitrile–nitromethane mixtures. In all cases, the exchange between free and complexed cesium ion was fast on the NMR time scale and only a single population average resonance was observed. The 133Cs chemical shift–mole ratio data indicated that the cesium ion forms 1:1 cation–ligand complexes with the investigated aza-crowns in all acetonitrile–nitromethane mixtures. The formation constants of the resulting complexes were evaluated from computer fitting of the chemical shift–mole ratio data. The stability of the resulting 1:1 complexes with Cs+ were found to vary in the order A18C6 > DBzDA18C6 > DA18C6. In all cases, there is the inverse relationship between the complex stability constants and the amount of acetonitrile in the mixed solvent.

133Cs NMR Study of Cs+ Ion Complexes with Dibenzo-24-crown-8, Dicyclohexano-24-crown-8 and Dibenzo-30-crown-10 in Binary Acetonitrile-Nitromethane Mixtures

Complexation of the cesium ion with the macrocyclic ligands: dibenzo-24-crown-8 (DB24C8), dicyclohexano-24-crown-8 (DC24C8) and dibenzo-30-crown-10 (DB30C10) was studied in binary acetonitrile-nitromethane mixtures by 133Cs NMR spectroscopy. The 133Cs chemical shift data indicated that the cesium cation forms 1:1 cation:ligand complexes with DB24C8 and DB30C10 but forms 2:1, 1:1 and 1:2 cation:ligand complexes with DC24C8 in acetonitrile-nitromethane mixtures. The formation constants of the complexes were calculated from the computer fitting of the chemical shift mole ratio data. The results show that the complex formation constants with the Cs+ cation vary in the order DC24C8>DB24C8∼DB30C10. It was found that the stability of the resulting complexes increases with increasing nitromethane concentration in the solvent mixture.

Structural and solution studies of new cadmium(II) complexes with 2,2′-diamino-4,4′-bithiazole

Two new Cd(II) complexes, [Cd(DABT)(CH3COO)2] (1) and [Cd(DABT)(NO3)2] (2), DABT = 2,2′-diamino-4,4′-bithiazole, have been synthesized and characterized by single crystal X-ray crystallography. In 1, each cadmium is chelated by two nitrogens of one DABT and four oxygens of acetate, whereas 2 is a dinuclear complex and there are two Cd's with eight and six coordination: Cd1O6N2 and Cd2O4N2 units. The counter ion effect of the complex formation reaction between cadmium(II) nitrate and acetate with DABT has been studied by spectroscopy. The formation constants of the 1 : 1 and 1 : 2 (metal ion to ligand) complexes were evaluated by computer fitting of the absorbance–mole ratio data.

Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Rb+ ion with 18-crown-6 in binary dimethylsulfoxide–nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Rb+ ion with 18-crown-6 (18C6) in a number of binary dimethylsulfoxide (DMSO)–nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 18C6 was fast on the NMR time scale and only a single population average 1H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of DMSO in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of formation constants. In all solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. The ∆H° versus T∆S° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reaction.

A spectrophotometric and thermodynamic study of the sitting-atop complex formation from reaction between free base meso-tetraarylporphyrins and zirconyl nitrate in chloroform solution

The sitting-atop complexation of meso-tetraarylporphyrins and its para-substituted derivatives (H 2t(4-X)pp, X:H, Br, Cl, CH(CH 3) 2, OCH 3, CH 3), as electron donors, with zirconyl, as an electron acceptor, have been investigated spectrophotometrically in chloroform. The mole ratio studies based on physicochemical techniques were employed clearly and revealed the formation of 1:1 sitting-atop complexes which was confirmed by UV–vis, 1H NMR and IR spectroscopic data. The value of the formation constant was estimated for each complex using a nonlinear optimization of the complex absorbance vs. mole ratio data by package KINFIT. The results showed that the stability of these complexes decreases with the temperature enhancement. Thermodynamic parameters, Δ G°, Δ H° and Δ S°, of the SAT complexes have been determined from the temperature dependence of formation constants by Van’t Hoff equation. Also, the influence of the substituents of the aryl rings in H 2t(4-X)pp on the stability of the SAT complexes is discussed.

Synthesis, characterization and the thermodynamic study of intermediate sitting-atop (i-SAT) complexes of free base meso-tetraarylporphyrins with InCl 3

The reaction of free base para-substituted meso-tetraarylporphyrins (H 2T( p-X)PP, X = H, OMe, Me, and Cl) with indium(III) chloride in CHCl 3 and mild conditions produced intermediate sitting-atop (i-SAT) complexes, [InCl 2(H 2T( p-X)PP)]InCl 4, as sole products. In the proposed structures of these complexes, four pyrrole rings are tilted alternatively up and down the porphyrin plane. This distortion makes suitable orientation of lone pairs of two pyrrolenine nitrogens for electron donation to an indium center of InCl 2 + cation. The 1:2 (porphyrin:indium) formation constant of resulting i-SAT complexes were calculated by the computer fitting of the complexes absorbance versus mole ratio data based on appropriate equations. Thermodynamic parameters, Δ G 0, Δ H 0, and Δ S 0, have been determined and the influence of electron donation of the para-substituted aryl groups in the free base porphyrins on the stability of the complexes is discussed.

Thermodynamic studies of sitting-atop (SAT) complexation of uranyl and free base meso -tetraarylporphyrins

The interaction of uranyl with meso-tetraphenylporphyrin and its para-substituted derivatives (H2t(4-X)pp, X : H, Br, Cl, CH(CH3)2, OCH3, CH3) in chloroform produced 1 : 1 sitting-atop (SAT) complexes ((uranyl)H2t(4-X)pp). Formation constants were calculated by computer fitting of complex absorbance versus mole ratio data to appropriate equations and found to decrease with temperature increase. Thermodynamic parameters, ΔG 0, ΔH 0 and ΔS 0 were obtained. The formation constants vary with changing of the substituent on the aryl rings of H2t(4-X)pp in the following order: (uranyl)H2t(4-OCH3)pp > (uranyl)H2t(4-CH3)pp > (uranyl)H2t(4-CH(CH3)2)pp > (uranyl)H2tpp > (uranyl)H2t(4-Br)pp > (uranyl)H2t(4-Cl)pp.

Spectrophotometric Studies of the Thermodynamics of Molecular Interaction between Some Free Base meso-Tetraarylporphyrins and SbF3

Abstract Spectrophotometric study was applied to the interaction of SbF3 with para-, meta-, and ortho-substituted meso-tetraarylporphyrins (H2t(Xp)p; X: H, OCH3, CH3, and Cl) in CHCl3. The 1:1 formation constants of the resulting complexes were calculated at several temperatures by the computer fitting of absorbances of solutions versus mole ratio data with appropriate equations. Thermodynamic parameters (ΔG0, ΔH0, and ΔS0) have been determined and the influence of electron donation and steric effect of the substituted aryl groups in the free base porphyrins on the stability of the complexes is discussed.

Spectrophotometric evaluation of stability constants of 1 : 1 weak complexes from mole ratio data using the bilogarithmic hyperbolic cosine method

A bilogarithmic hyperbolic cosine method for the spectrophotometric evaluation of stability constants of 1 : 1 weak complexes is developed and applied to data found in the literature. The method devised does not require any approximations and the variables of the final equation proposed are well separated, being, in addition, the abscissa free from error, which facilitates the application of least squares analysis. The proposed method also provides a closed-scale representation of variables, unlike other plots, and agrees well with the nonlinear regression method.

Conductance Study of the Thermodynamics of Complexation of K+, Rb+, Cs+ and Tl+ Ions with Dibenzo-24-crown-8 in Binary Acetonitrile–Nitromethane Mixtures

The complexation reactions between dibenzo-24-crown-8 (DB24C8) and K+, Rb+, Cs+ and Tl+ ions were studied conductometrically in different acetonitrile–nitromethane mixtures at various temperatures. The formation constants of the resulting 1:1 complexes were calculated from the computer fitting of the molar conductance–mole ratio data at different temperatures. At 25 °C and in all solvent mixtures used, the stability of the resulting complexes varied in the order Tl+ > K+ > Rb+ > Cs+. The enthalpy and entropy changes of the complexation reactions were evaluated from the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture. The TΔS° vs. ΔH° plot of all thermodynamic data obtained shows a fairly good linear correlation indicating the existence of enthalpy–entropy compensation in the complexation reactions.

<b>Spectrophotometric and electrochemical studies of the interaction of cryptand 222 with DDQ and I<sub>2</sub> in ethanol solution</b>

Spectrophotometric and electrochemical studies concerning the interaction of cryptand 222 with DDQ and I 2 have been performed in ethanol solution. In the case of DDQ, the results are indicative of the formation of C222 + and DDQ - through an equilibrium reaction. The results of I 2 indicate the formation of I 2 -ethanol complex and I 3 - in the absence of C222. In the presence of C222, the formation of C222I + and I 3 - through a non-equilibrium reaction is confirmed. The equilibrium constant of the redox reaction between DDQ and C222 has been calculated from the absorbance mole ratio data, using the nonlinear least square program “KINFIT”. The electrochemical reversibility of I - /I 2 couple and irreversibility of DDQ/DDQ - is indicated by amperometry. The behavior of DDQ and I 2 has been compared. A comparison with aprotic solvents has also been made. KEY WORDS : Spectrophotometry, Electrochemistry, Cryptand 222, DDQ, I 2 Bull. Chem. Soc. Ethiop. 2006 , 20(2), 183-192.

A bilogarithmic method for the spectrophotometric evaluation of stability constants of 1:1 weak complexes from mole ratio data

The absorbance changes that occur when the mole ratio of the components of ligand complex equilibria is varied while the concentration of one component is kept constant (mole ratio method) allow evaluating stability constants in favourable conditions. Values of the corresponding stability (association) constants are normally assigned on the basis of spectrophotometric analysis. Determination of stability constants can be performed by a number of linear procedures, but most of these, suffer from theoretical and practical drawbacks, e.g., linear transformation of the rectangular hyperbola type of binding constants, is valid only when one of the two species is present in a large excess. A rigorous treatment of the experimental mole ratio data for 1:1 weak complexes is carried out in this paper with the aim of eliminating some of the assumptions involved in the other methods usually applied for evaluating stability constants. Orthogonal regression is required in order to take into account the error in both axes. The method has been applied to literature data for the iron(III)-thiocyanate and nickel(II)-selenocyanate systems, as well as to a number of host–guest cyclodextrin complexes.

Spectroscopic and conductometric studies of molecular complex formation between 2,4,6-trinitrophenol and diaza-18-crown-6, tetraaza-14-crown-4 and cryptand C222 in 1,2-dichloroethane solution

The formation of molecular complexes between 2,4,6-trinitrophenol (TNP) and aza-substituted macrocycles diaza-18-crown-6 (DA18C6), tetraaza-14-crown-4 (TA14C4) and cryptand C222 in 1,2-dichloroethane solution was investigated spectrophotometrically and conductometrically. The mole ratio and continuous variations studies based on both physicochemical techniques employed clearly revealed the formation of both 1:1 and 2:1 (TNP:macrocycle) adducts in solution. Formation of the resulting complexes was also confirmed by 1H NMR and IR spectroscopic studies. Formation constants of the resulting complexes were evaluated from computer fitting of the corresponding mole ratio data. Stability of the resulting complexes was found to vary in the order C222 ≈ TA14C4 > DA18C6.

23Na NMR Studies of Stoichiometry and Stability of Sodium Ion Complexes with Several Crown Ethers in Binary Acetonitrile–Dimethylformamide Mixtures

23Na NMR measurements were employed to monitor the stability of Na+ ion complexes with 18-crown-6 (18C6), dicycloxyl-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6), 15-crown-5 (15C5) and benzo-15-crown-5 (B15C5) in binary acetonitrile–dimethylformamide mixtures of varying composition. In all cases, the variation of 23Na chemical shift with [crown]/[Na+] mole ratios indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation which relates the observed chemical shifts to the formation constants. It was found that, in pure acetonitrile, the stabilities of the resulting 1:1 complexes vary in the order 15C5>DC18C6>B15C5>18C6>DB18C6, while in pure dimethylformamide the stability order is DC18C6>18C6>15C5>B15C5>DB18C6. The observed changes in the stability order could be related to the specific interactions between some crown ethers and acetonitrile. It was found that, in the case of all complexes, an increase in the percentage of dimethylformamide in the solvent mixtures would significantly decrease the stability of the complexes.

The interaction between ketamine and some crown ethers in common organic solvents studied by NMR: The effect of donating atoms and ligand structure

1H NMR spectroscopy was used to investigate the stoichiometry and stability of the drug ketamine cation complexes with some crown ethers, such as 15-crown-5 (15C5), aza-15-crown-5 (A15C5), 18-crown-6 (18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6), dibenzyl-diaza-18-crown-6 (DBzDA18C6) and cryptant [2,2,2] (C222) in acetonitrile (AN), dimethylsulfoxide (DMSO) and methanol (MeOH) at 27 °C. In order to evaluate the formation constants of the ketamine cation complexes, the CH 3 protons chemical shift (on the nitrogen atom of ketamine) was measured as function of ligand/ketamine mole ratio. The formation constant of resulting complexes were calculated by the computer fitting of chemical shift versus mole ratio data to appropriate equations. A significant chemical shift variation was not observed for 15C5 and 18C6. The stoichiometry of the mono aza and diaza ligands are 1:1 and 1:2 (ligand/ketamine), respectively. In all of the solvents studied, DA18C6 formed more stable complexes than other ligands. The solvent effect on the stability of these complexes is discussed.

SPECTROPHOTOMETRIC STUDY OF THE INTREACTION OF SOME BENZO, BENZYL AND PHNYLCROWN ETHERS WITH P-ACCEPTOR DDQ IN CHLOROFORM SOLUTION

The interaction between benzo-15-crown-5 (B15C5), dibenzo-18-crown-6 (DB18C6), dibenzyl-daza-18crown-6 (DBzDA18C6), N-phenyl-aza-15-crown-5 (NPhA15C5) and dibenzopyridine-18-crown-6 (DBPy18C6) with π-acceptor 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in chloroform solution was studied spectrophotometrically. The interaction of B15C5-DDQ and DB18C6-DDQ caused the formation of 1:1 charge transfer complexes through equilibrium reaction. The interaction of others caused the formation of 1:1 complexes in an equilibrium step and the conversion of the resulting adduct to D+DDQ- (D=NPhA15C5, DBPy18C6, DBzDA18C6) in a nonequilibrium step. The formation constant of DBzDA18C6 was evaluated by computer fitting of the absorbance mole ratio data. Other stability constants were evaluated through the Hildebrand method. It was found that the stabilities vary in the order: B15C5 < DB18C6 < DBPy18C6 < NPhA15C5 < DBzDA18C6. All of the resulting molecular complexes were isolated in crystalline form and characterized.

Lithium-7 NMR Study of Several Li+-Crown Ether Complexes in Binary Acetone-Nitrobenzene Mixtures

7Li NMR measurements were employed to monitor the stoichiometry andstability of Li+ ion complexes with 12-crown-4 (12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) l8-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6) in binary acetone-nitrobenzene mixtures of varying composition. In all cases studied, the variation of 7Li chemical shift with the crown/Li+ mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all solvent mixtures used, the stabilities of the resulting 1:1 complexes varied in the order15C5 > B15C5 > DC18C6 > 18C6 > 12C4 >DB18C6. It was found that,in the case of all complexes, an increase in the percentage of acetone in thesolvent mixtures significantly decreased the stability of the complexes.

Spectrofluorimetric Study of the Complexes Between Calcein and Lanthanide(III) Ions

ABSTRACT The equilibrium of calcein, an H6L type fluorescent ligand, with lanthanide(III) ions, Ln(III), was studied spectrofluorimetrically in aqueous solution at constant ionic strength =0.1 (KC1), pH 8.0 and 25.0±0.1°C. Application of the mole ratio and continuous variation methods reveals the formation of 1:1 complexes. The conditional stability constants (β') were calculated from the analysis of the observed fluorescence vs. [Ln(III)]/[calcein] mole ratio data by using an iterative non-linear least-squares computer program. The values obtained for β' are in the range 5.24×106-5.77×107 The thermodynamic stability constant (β) were estimated by calculating the sidereaction coefficients (α) fro lanthanides and calcein. The β values obtained were from 3.2×1012 to 3.6×1013

Sandwich and Mixed Sandwich Complexes of the Cesium Ion with Crown Ethers in Nitromethane

Cesium-133 nuclear magnetic resonance was used as a probe of the interaction of the Cs+ ion with the crown ethers 18C6, 15C5, 12C4, and with HMHCY (hexamethyl hexacyclen) in nitromethane solution with thiocyanate as the counterion. A study of the 133Cs chemical shift as a function of crown to Cs+ mole ratio showed that the complexation reactions occur stepwise. Formation of a 1:1 complex is followed by the addition of a second complexant molecule to form a sandwich cation. In the case of 18C6, there is strong evidence for the intermediate formation of a 3:2 adduct. The formation constants of sandwich complexes that contain two molecules each of 18C6, 15C5, and HMHCY and various mixed sandwiches of these complexants (and also 12C4) in solution were evaluted from the mole ratio data. The crystal structure of the mixed sandwich salts Cs+(18C6)(12C4)SCN-·2(CH3OH) and Rb+(18C6)(12C4)I-·H2O were also determined.