Binary Mixed Solvent Solutions Research Articles

Study of Complex Formation between Kryptofix 21 with La3+, Y3+ and Ce3+ Cations in Some Binary Mixed Non-Aqueous Solvents Using the Conductometric Method

The complexation reactions between La3+, Y3+ and Ce3+ cations with the macrocyclic ligand, kryptofix 21, were studied in methanol-acetonitrile (MeOH-AN) and methanol-methylacetate (MeOHMeOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most solvent systems, the kryptofix 21 forms a 1: 1 [M: L] complex with La3+, Y3+ and Ce3+ metal cations, but in the case of Y3+ cation in pure methylacetate, in addition of formation of a 1: 1 [ML] complex, 1: 2 [ML2] and 1: 3 [ML3] complexes are formed in solution. In the case of Ce3+cation, a 1: 1 [ML] and also a 1: 2 [ML2] complexes are formed in this solvent system at all studied temperatures. The electrical conductance data in acetonitrile, show that a 1: 1 [ML] and also a 1: 2 [ML2] complexes are formed between the ligand and La3+ and Ce3+ metal cations at different temperatures. The stability constants of the 1: 1 [ML] complexes were determined using the conductometric data and a computer program, GENPLOT. A non-monotonic relationship was observed between logKf of the 1: 1 complexes with the composition of the binary solvent solutions which was discussed in term of solvent-solvent interactions and also preferential solvation of the metal cations and the ligand in solutions. The selectivity order of the ligand for the metal cations in MeOH–AN and MeOH–MeOAc binary solvent solutions, at 25°C was found to be: Y3+ > La3+ > Ce3+ and La3+ > Y3+ > Ce3+, respectively. The values of the standard thermodynamic quantities (ΔHc° and ΔSc°) for formation of the 1: 1 complexes were obtained from temperature dependence of the stability constans of the complexes and the results show that the thermodynamics of the complexation reactions between kryptofix 21 and La3+, Y3+ and Ce3+ cations, is affected by the nature and composition of the mixed solvents systems.

A thermodynamic study of interaction of Ag+, Mg2+, Ca2+, and K+ cations with 4-hydroxyphenyl-2,5-bis(2-benzofuranyl)pyridine in some binary mixed non-aqueous solvents

In the present work the complexation process between Ag+ and Mg2+ cations and 4-hydroxyphenyl-2,5-bis(2-benzofuranyl)pyridine (HBFPY) ligand was studied in pure dimethylformamide (DMF), ethanol (EtOH), acetonitrile (AN) and in (DMF-EtOH), (AN-EtOH) and (DMF-AN) binary mixed solvent solutions at different temperatures using the conductometric method. Also in this work the complexation reaction between Ca2+, K+ cations and HBFPY ligand, was studied in pure dimethylformamide (DMF), propanol (PrOH), 1,4-dioxane (DOX), ethanol (EtOH) and in DMF-PrOH, DMF-DOX and DMF-EtOH binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between this ligand and the studied cations is 1 : 1 [ML]. In most cases, addition of HBFPY to solutions of these cations, causes a continuous increase in the molar conductivities which indicates that the mobility of complexed cations is more than the uncomplexed ones. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, GENPLOT. The stability constant of [Mg(HBFPY)]2+ complex in various neat solvents at 15°C decreases in order: EtOH > DMF > AN and the stability constant of [Ag(HBFPY)]+ complex in various neat solvents at 35°C decreases in order: DMF > EtOH. The values of standard enthalpy changes (ΔH°c) for complexation reactions were obtained from the slope of the Van’t Hoff plots and the changes in standard entropy (ΔS°c) were calculated from the relationship ΔH°c,295.15= ΔH°c–298.15ΔS°c.

Complexation process between La3+ cation and 4′-nitrobenzo-15-crown-5 in some binary mixed non-aqueous solvent

The complexation reaction between 4′-nitrobenzo-15-crown-5 (4′-NB15C5) with La3+ cation was studied in ethanol-acetonitrile (EtOH-AN), ethanol-methylacetate (EtOH-MeOAc), ethanol-1,2 dichloroethane (EtOH-DCE), and ethanol-nitrobenzene (EtOH-NB) binary mixed solvent solutions at different temperatures using the conductometric method. The results show that in most cases, the stoichiometry of the complex formed between 4′-NB15C5 and La3+ cation is 1: 1 [ML]. The stability constant of (4′-nitrobenzo-15C5La)3+ complex changes by the nature and composition of the solvents systems. The stability order of (4′-nitrobenzo-15C5La)3+ complex in the binary mixed solvents with 10 mol % of ethanol at 25°C was found to be: EtOH-MeOAc > EtOH-NB > EtOH-AN ~ EtOH-DCE. A non-linear behavior was observed for variations of logKf of the complex in terms of the solvent composition. The standard values of the thermodynamic parameters (ΔHc° ΔSc°) for complexation reaction were obtained from temperature dependence of the stability constant of the complex and the results show that, in most solvent systems, the complexation reaction between La3+ and 4′-NB15C5 is entropy stabilized, but from enthalpy view point, except in a few cases, it is athermic.

Thermodynamic study of complex formation between Kryptofix-5 and Sn2+ in several individual and binary non-aqueous solvents using a conductometric method

The complex formation between 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix-5) and Sn2+ ions was studied in pure acetonitrile (AN), dimethylformamide (DMF), 1,4-dioxane (DOX), and methanol (MeOH) and in acetonitrile-1,4-dioxane (AN-DOX), acetonitrile-dichloromethane (AN-DCM), acetonitrile-methanol (AN-MeOH), and acetonitrile-dimethylformamide (AN-DMF) binary mixed solvent solutions at different temperatures using conductometric method. 1: 1 [ML] complex is formed between the metal cation and ligand in most solvent systems but in the cases of AN-MeOH (MeOH = 90 mol %) binary mixture and in pure MeOH a 2: 1 [M2L] complex was observed, that is the stoichiometry of complexes may be changed by the nature of the medium. The stability order of the (Kryptofix-5·Sn)2+ complex in the studied binary mixed solvent solutions at 25°C was found to be AN-DOX > AN-DCM > AN-MeOH > AN-DMF and in the case of pure solvents at 25°C the sequence was the following: AN > DMF > DOX. A non-linear behavior was observed for changes of logK f of (Kryptofix-5·Sn)2+ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent intractions and also by the preferential solvation of the f species involved in the complexation reaction. The values of standard enthalpy changes (ΔH c ○ ) for complexation reactions were obtained from the slope of the Van’t Hoff plots and the changes in standard entropy (ΔS c ○ ) were calculated from the relationship ΔG c, 298.15 ○ = ΔH c ○ − 298.15ΔS c ○ . The results show that in most cases, the (Kryptofix-5·Sn)2+ complex is both enthalpy and entropy stabilized.

Thermodynamic study of complex formation between Ce3+ and cryptand 222 in some binary mixed nonaqueous solvents

The stoichiometry, stability and the thermodynamic parameters of complex formation between cerium(III) cation and cryptand 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabycyclo[8.8.8]-hexacosane) were studied by conductometric titration method in some binary solvent mixtures of dimethylformamide (DMF), 1,2-dichloroethane (DCE), ethyl acetate (EtOAc) and methyl acetate (MeOAc) with methanol (MeOH), at 288, 298, 308, and 318 K. A model based on 1: 1 stoichiometry has been used to analyze the conductivity data. The data have been fitted according to a non-linear least-squares analysis that provide the stability constant, K f, for the cation-ligand inclusion complex. The results revealed that the stability order of [Ce(cryptand 222)]3+ complex changes with the nature and composition of the solvent system. A non-linear relationship was observed between the stability constant (logK f) of [Ce(cryptand 222)]3+ complex versus the composition of the binary mixed solvent. Standard thermodynamic values were obtained from temperature dependence of the stability constant of the complex, show that the studied complexation process is mainly entropy governed and are influenced by the nature and composition of the binary mixed solvent solutions.

Thermodynamic study of complex formation between Ni2+ and Co2+ cations and 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5) in binary mixed nonaqueous solutions

Conductometric titrations were performed in pure and binary solvent solutions of ethyl acetate (EtOAc), methyl acetate (MeOAc) and methanol (MeOH) with acetonitrile (AN) at 288, 298, 308, and 318 K to determine the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of nickel(II) and cobalt(II) cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5). The stability constants of the resulting 1:1 complexes formed between the metal cations and the ligand in different solvent mixtures were determined by computer fitting of the conductance-mole ratio data. The results revealed that the stability order of (kryptofix 5)-Ni2+ and (kryptofix 5)-Co2+ complexes changes with nature and composition of the solvent system. There is a non-linear relationship between the logKf values of complexes and the mole fraction of acetonitrile in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the nickel(II) and cobalt(II) cations with the acyclic ligand changes with the nature of the solvent. The enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, in most of systems, the complexation processes of nickel(II) and cobalt(II) cations with kryptofix 5, are both enthalpy and entropy stabilized and the values of these parameters are influenced by the nature and composition of the binary mixed solvent solutions.

Effect of solvent on complexation between Y3+ cation and 4,13-diaza-18-crown-6 in some binary mixed non-aqueous solvents

The complexation reaction of 4,13-diaza-18-crown-6 (DA18C6) with Y3+ cation was studied in some binary mixed solvent solutions of acetonitrile (AN) with methanol (MeOH), ethanol (EtOH), 2-propanol (2-PrOH) and methyl acetate (MeOAc) at different temperatures by conductometric method. The obtained data show that in all studied solutions the stoichiometry of the complex formed between DA18C6 and Y3+ cation is 1: 1 [ML], but in the case of pure MeOAc, a 2: 1 [ML2] complex is formed in solution upon addition of the ligand to the metal salt solution, and further addition of the ligand results in formation of a M2L2 complex in solution. This results show that the stoichiometry of the composition of the macrocyclic complexes may be affected by the nature of the solvent system. The results obtained in this study show that the stability constant of the resulting 1: 1 [ML] complex in the binary solvent solutions decreases in the order: AN-MeOAc > AN-2PrOH > AN-MeOH > AN-EtOH. A non-linear relationship was observed between the stability constant (logKf) of [Y(DA18C6)]3+ complex with the composition of the binary mixed solvent solutions. The corresponding standard thermodynamic parameters (H°c, Δ S°c) for 1: 1 [ML] complexation reaction between DA18C6 and Y3+ cation were obtained from temperature dependence of the stability constant of the complex. The results show that, in all solvent systems, the (DAI8C6.Y)3+ complex is entropy stabilized, but from enthalpy point of view, depending on the solvent system, it is stabilized or destabilized and the result show that the values of both thermodynamic quantities change with the nature and composition of the binary mixed solvent solutions.

Study of complex formation process between 4′-nitrobenzo-18-crown-6 and yttrium(III) cation in some binary mixed non-aqueous solvents using the conductometry method

The complexation reaction between Y3+ cation and macrocyclic ligand, 4′-nitrobenzo-18-crown-6 (4′NB18C6), was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–1,2-dichloroethane (AN–DCE), acetonitrile–dimethylformamide (AN–DMF) and acetonitrile–ethylacetate (AN–EtOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most cases, the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation is 1:1 [M:L], but in the case of AN-DCE binary solution (mol% DCE=50) at 15, 25 and 35°C, a 2:1 [M2:L] and also a 2:2 [M2:L2] complexes are formed in solution. The results show that the stoichiometry of the complex formed between 4′NB18C6 and Y3+ cation changes with the composition of the mixed solvents and even with temperature. The stability constant of the 1:1 complex was determined using a computer program, GENPLOT. The stability order of (4′NB18C6.Y)3+ complex in pure studied solvents at 25°C was found to be: EtOAc>AN>MeOH>DMF and in the case of the mixed solvent solutions with 25mol percent of AN at 25°C was: AN-DCE>AN-EtOAc>AN-MeOH∼AN-DMF. The values of stability constant (logKf) of (4′NB18C6.Y)3+ complex which were obtained from conductometric data, show that the stability of the complex is not only affected by the nature and composition of the solvent system, but it is also influenced by the temperature. In all cases, a non-linear behavior is observed for changes of logKf of the (4′NB18C6.Y)3+ complex versus the composition of the binary mixed solvents. The values of standard thermodynamic quantities (ΔH°c and ΔS°c) for the complexation process which were obtained from temperature dependence of the stability constant of (4′NB18C6.Y)3+ complex, show that depending on the solvent system, in most cases, the complex is enthalpy and also entropy stabilized, but in some cases, it is stabilized or destabilized from these view points.

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 logKf 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.

Complexation study of cryptand 222 with lanthanum(III) cation in binary mixed non-aqueous solvents

Conductometric titrations have been performed in some binary solvent solutions of acetonitrile (AN), 1,2-dichloroethane (DCE), ethylacetate (EtOAc) and methylacetate (MeOAc) with methanol (MeOH), at 288, 298, 308, and 318 K to give the complex stability constant and the thermodynamic parameters for the complexation of lanthanum(III) cation with 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane (cryptand 222). The stability constant of the resulting 1:1 complex at each temperature was determined from computer fitting of the conductance-mole ratio data. The results revealed that, the stoichiometry and the stability order of (cryptand 222 · La)3+ complex changes with the nature and also the composition of the solvent system. A non-linear relationship was observed between the stability constant (logKf) of (cryptand 222 · La)3+ complex versus the composition of the binary mixed solvents. Thermodynamically, the complexation of lanthanum(III) cation with the cryptand 222, is mainly entropy governed and the values of these parameters are influenced by the nature and composition of the binary mixed solvent solutions.

Solvent influence upon complex formation between kryptofix5 and Cd2+ in some pure and binary mixed non-aqueous solvents using conductometry

The complexation reaction of Cd2+ with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix5) was studied in pure acetonitrile (AN), ethylacetate (EtOAc), methanol (MeOH), dimethylformamide (DMF), and in acetonitrile-ethylacetate (AN–EtOAc), acetonitrile-dimethylformamide (AN–DMF), methanol-acetonitrile (MeOH–AN), and dimethylformamide-ethylacetate (DMF–EtOAc) binary mixed solvent solutions at different temperatures using conductometric method. The conductance data show that the stoichiometry of the complex in all solvent systems, is 1 : 1 [ML]. The fitting and experimental curves were obtained from Sigma plot computer program to make it more clear of the 1 : 1 [ML] complexation model. The stability constant of (kryptofix5·Cd)2+ complex was obtained using a GENPLOT computer program. The results show that the stability of (kryptofix5·Cd)2+ complex at all studied temperatures in the binary solvent solutions decreases in order: AN–EtOAc > AN–MeOH > AN–DMF ∼ EtOAc–DMF and in pure non-aqueous solvents, the stability order of the complex was found to be: AN > EtOAc > MeOH > DMF. The values of standard thermodynamic parameters (, ) for formation of the complex were obtained from temperature dependence of the stability constant using the van’t Hoff plot. The results show that in most cases, the complex formation reaction between kryptofix5 and Cd2+ is entropy stabilized.

Complexing ability of kryptofix5 with Ag+ in some binary mixed solvents at different temperatures

The stability constant (log Kf ) for complexation of 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix5) with Ag+ has been determined conductometrically in acetonitrile–ethyl acetate (AN–EtOAc), methanol–ethyl acetate (MeOH–EtOAc), methanol–water (MeOH–H2O) and dimethyl sulfoxide–ethyl acetate (DMSO–EtOAc) solutions at different temperatures. A 1 : 1 [ML] complex was formed between the metal cation and ligand in most solvent systems. The stability constant of the resulting 1 : 1 complex was determined from computer fitting of the conductance–mole ratio data. The stability order of the (kryptofix5.Ag)+ complex in the studied binary mixed solvent solutions at 25°C was found to be MeOH–EtOAc > AN–EtOAc > DMSO–EtOAc. The results show that in some cases the stoichiometry of the complex formed between Ag+ and the ligand changes with the nature of the solvent and that solvation numbers of the metal cation and the resulting complexes change with temperature. The values of the standard thermodynamic parameters (, ) show that in all cases the (kryptofix5.Ag)+ complex is entropy stabilized, but the enthalpy, depending on solvent system, is stabilizing or destabilizing.

Thermodynamics of ZrO2+ cation complexation with dibenzo-18-crown-6 in mixed non-aqueous solvents

The complexation reaction of dibenzo-18-crown-6 (DB18C6) with ZrO2+ cation was studied in some binary solvent solutions of acetonitrile (AN), 1,2 dichloroethane (DCE), nitromethane (NM) and ethylacetate (EtOAc) with methanol (MeOH), at different temperatures by conductometry method. The stability constant of the resulting 1:1 complex at each temperature was determined using a computer fitting conductance-mole ratio data. The results revealed that, the (DB18C6·ZrO)2+ complex is more stable in the EtOAc–MeOH binary mixed solvents compared with the other binary mixed solvent solutions. A non-linear relationship was observed for changes of log Kf of (DB18C6·ZrO)2+ complex versus the composition of the binary mixed solvents. The corresponding standard thermodynamic parameters (ΔH c ° , ΔS c ° ) were obtained from temperature dependence of the stability constant. The results show that the (DB18C6·ZrO)2+ complex is enthalpy destabilized but entropy stabilized and the values along with the sign of these parameters are influenced by the nature and composition of the mixed solvents.

Spectroscopic Studies of Fullerene Aggregates

The growth and structure of fullerene (C60 and C70) aggregates in single and binary mixed-solvent solutions were examined by light scattering and photoluminescence spectroscopy. Solute aggregation exhibiting reaction-limited kinetics was observed to occur over a period of several days in ∼1 mM C60 solutions in benzene. Aggregation was irreversible and could be suppressed by addition of a soluble radical scavenger, suggesting a radical mechanism for aggregate formation. Dynamic light scattering measurements determined that the aggregates attain a hydrodynamic radius of ∼300 nm before sedimentation occurs. Solutions containing stable suspensions of fullerene aggregates were also prepared by addition of a poor solvent to a solution of fullerene in a strong solvent. Both static and dynamic light scattering methods were used to determine the mass, hydrodynamic radius, radius of gyration, and fractal dimension of the aggregates. Photoluminescence spectra of aggregates were compared with those of the crystalline materials. The luminescence spectra of solutions containing aggregates were found to differ substantially from the luminescence spectra of unassociated fullerene. The chief effect of aggregate formation is the appearance of excimer-like features in the photoluminescence spectrum.