Acetonitrile Dimethylformamide Research Articles

Complexation Study of Kryptofix22DD with Ag+ Cation in Some Mixed Non-aqueous Binaries Solutions

The complexation reactions between Kryptofix22DD, with Ag+ cation, was studied in acetonitrile-dimethylformamide (AN-DMF), acetonitrile- tetrahydrofuran(AN-THF), methanol- tetrahydrofuran (MeOH-THF) and methanol-dimethylformamide (MeOH-DMF) binary non-aqueous dissolvable arrangements at various temperatures utilizing the conductometric strategy. The conductance information shows that in all cases, the complex stoichiometry framed between the macrocyclic ligand and the metal cation is 1:1 [ML]. The experimental results indicate that in any event, the complex stoichiometry formed between the Ag+ and the Kryptofix22DD macrocyclic ligand is 1:1 (ML). The qualities the development constants of the complex have been amassed by plotting the molar conductivity bends-utilizing program, GENPLOT. A nonlinear relationship was observed between the complex's stability constant (log Kf) and the binary solvent composition. The values standard thermodynamic parameters (ΔHc° and ΔSc°) have been determined Dependence of the temperature of constant stability of the complex using van't Hoff plots. The results show that thermodynamic quantities are dependent on nature and Binary Solvent Composition solutions.

Solvent influence on complex formation between Cd2+ and 2-hydroxy-1,4-naphthoquinone in binary mixed nonaqueous solvents at 15–45°C

The complexation reaction of Cd2+ cation with 2-hydroxy-1,4-naphthoquinone (HNQ) was studied in acetonitrile (AN), 2-PrOH, ethyl acetate (EtOAc), EtOH, dimethylformamide (DMF) and in binary solutions AN–2-PrOH, AN–DMF, AN–EtOH, and AN–EtOAc using conductometric method at 15–45°C. The conductance data show that the stoichiometry of the Cd2+ complex with HNQ in all solvent systems is 1 : 1. In the pure solvents the stability of the complex changes in the order AN > 2-PrOH > EtOH > DMF. The stability of the complex at 25°C in the studied mixtures changes in the following order : AN−EtOAc > AN−2-PrOH > AN−EtOH > AN−DMF. These orders are affected by the nature and composition of the solvent systems and by the temperature. From the temperature dependence data, the thermodynamic functions values (ΔH° and ΔS°) for the complex formation were calculated.

A thermodynamic study of complexation process between N,N′-dipyridoxylidene(1,4-butanediamine) and Cd2+ in some binary mixed solvents using conductometry

Complexation of the Cd2+ ion with N,N′-dipyridoxylidene(1,4-butanediamine) Schiff base was studied in pure solvents including acetonitrile (AN), ethanol (EtOH), methanol (MeOH), tetrahydrofuran (THF), dimethylformamide (DMF), water (H2O), and various binary solvent mixtures of acetonitrile–ethanol (AN–EtOH), acetonitrile–methanol (AN–MeOH), acetonitrile–tetrahydrofuran (AN–THF), acetonitrile–dimethylformamide (AN–DMF), and acetonitrile–water (AN–H2O) systems at different temperatures using the conductometric method. The conductance data show that the stoichiometry of complex is 1: 1 [ML] in all solvent systems. A non-linear behavior was observed for changes of log K f of [Cd(N,N′-dipyridoxylidene(1,4-butanediamine)] complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions. The results show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents.

Conductometric studies on complexation of Ag+ cation by C-thiophene calix[4]resorcinarene in pure and mixed non-aqueous solvent systems

The present work relates to the complexation reaction between a new ionophore C-thiophenecalix[4]resorcinarene (C-TC[4]R) with Ag+ cation in pure acetonitrile (ACN), methanol (MeOH), ethanol (EtOH), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) and their binary mixtures by conductometric method. The conductance data showed that the stoichiometry of the complexes formed in pure as well as binary solvent mixtures was 1:1 (Ag+: C-TC[4]R). The stability of C-TC[4]R complexes with Ag+ metal ion was observed to be sensitive to the nature of the solvent system. The results obtained show that the selectivity of C-TC[4]R for Ag+ cation in pure solvents followed the order MeOH > DMF > EtOH > DMSO > ACN. In binary solvent systems, there was a linear change in log K f values for all the binary mixtures (ACN–DMF, ACN–DMSO, MeOH–DMF, EtOH–DMF and EtOH–DMSO) except MeOH–DMSO. The results show that the complexation reactions were spontaneous and entropy (∆S°) as well as enthalpy (∆H°) stabilized in all the solvent systems except EtOH–DMSO, in which the complexes were entropy destabilized. A linear relationship between ΔH° and ΔS° values indicate the existence of entropy–enthalpy compensation in the formation of [Ag–C-TC[4]R]+ complex in all the solvent systems studied.

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.

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.

NMR Study of the Stoichiometry and Stability of 30-Crown-10 Complexes with Ca2+, Sr2+, Ba2+ and Pb2+ Cations in Acetonitrile–Dimethylformamide Binary Mixtures

The complexation reaction of 30-crown-10 (30C10) with Ca2+, Sr2+, Pb2+ and Ba2+ ions in a various deuterated acetonitrile–dimethyformamide binary mixtures was studied using proton nuclear magnetic resonance spectroscopy. The complexes were found to have a 1:1 ratio and their stability is in the order of Ba2+ > Pb2+ > Sr2+ > Ca2+. It was observed that the donicity of the solvents as expressed by the Gutmann donor numbers and stability of the resulting complexes have an inverse relationship.

Spectroscopic and DFT study of solvent effects on the electronic absorption spectra of sulfamethoxazole in neat and binary solvent mixtures

The solvatochromic behavior of sulfamethoxazole (SMX) was investigated using UV–vis spectroscopy and DFT methods in neat and binary solvent mixtures. The spectral shifts of this solute were correlated with the Kamlet and Taft parameters (α, β and π*). Multiple lineal regression analysis indicates that both specific hydrogen-bond interaction and non specific dipolar interaction play an important role in the position of the absorption maxima in neat solvents. The simulated absorption spectra using TD–DFT methods were in good agreement with the experimental ones. Binary mixtures consist of cyclohexane (Cy)-ethanol (EtOH), acetonitrile (ACN)-dimethylsulfoxide (DMSO), ACN–dimethylformamide (DMF), and aqueous mixtures containing as co-solvents DMSO, ACN, EtOH and MeOH. Index of preferential solvation was calculated as a function of solvent composition and non-ideal characteristics are observed in all binary mixtures. In ACN–DMSO and ACN–DMF mixtures, the results show that the solvents with higher polarity and hydrogen bond donor ability interact preferentially with the solute. In binary mixtures containing water, the SMX molecules are solvated by the organic co-solvent (DMSO or EtOH) over the whole composition range. Synergistic effect is observed in the case of ACN–H2O and MeOH–H2O, indicating that at certain concentrations solvents interact to form association complexes, which should be more polar than the individual solvents of the mixture.

Synthesis, spectroscopy, fluorescence and crystal structures of cyclopalladated dinuclear complexes with C, N-chelating azobenzenes and N, S-bridging heterocyclic-2-thiolates

Reaction of palladium(II) chloride with azobenzene (azb) in acetonitrile-dimethyl formamide mixture followed by the addition of pyridine-2-thione (pySH) yielded dark reddish brown compound [Pd2(κ2-μ-N, S-pyS)2(κ2-C, N-azb)2] 1. Similarly, dark reddish brown compound [Pd2(κ2-μ-N, S-pymS)2(κ2-C, N-azb)2] 2 incorporating pyrimidine-2-thiolate (pymS−) was obtained. The p-methoxyazobenzene (p-mazb) has formed similar complexes, [Pd2(κ2-μ-N, S-pyS)2(κ2-C, N-p-mazb)2] 3 and [Pd2(κ2-μ-N, S-pymS)2(κ2-C, N-p-mazb)2] 4. The method of preparation of 3 and 4 involved reaction of pyridine-2-thione (3)/pyrimidine-2-thione (4) with orange [Pd(κ2-C, N-p-mazb)(κ2-μ-Cl)]2 precursor suspended in dichloromethane followed by the addition of Et3N base. Complexes crystallized in triclinic (1, P-1) and monoclinic (P21/n, 2; C2/c, 3 and 4) systems. Complex 1 exists as a polymorph to a reported structure and has two crystallographically independent dimeric molecules in the asymmetric unit unlike one molecule each in 2–4. Both the thio-ligands act as N, S-bridging in the dimers prepared while the azb and p-mazb are C, N-chelating. It is the p-methoxyphenyl ring of p-mazb which ortho-palladates in 3 and 4, unlike the phenyl ring palladation in 1 and 2. The metal–metal separation were relatively short in complexes 2 {2.851(1) Å} and 4 {2.854(1) Å} having pymS− bridging anions and were long in 1 {2.898(2) Å} and 3 {2.882(1) Å} complexes having pyS− bridging anions.

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.

Study of complex formation between C18H36N2O6 and [formula omitted] cation in some binary mixed non-aqueous solutions

The complexation reaction between UO22+ cation and the macrobicyclic ligand C18H36N2O6 was studied in acetonitrile–dimethylformamide (AN–DMF), acetonitrile–tetrahydrofuran (AN–THF), acetonitrile–dichloromethane (AN–DCM) binary solvent solutions at different temperatures using the coductometric method. In most cases, C18H36N2O6 forms a 1:1 [M:L] complex with the UO22+ cation. But in some of the studied solvent systems, in addition to formation of a 1:1 complex, a 1:2 [M:L2] complex is formed in solution. A non-linear behavior was observed for changes of logKf of the (C18H36N2O6·UO2)2+ complex versus the composition of the binary mixed solvents. The sequence of the stability of the (C18H36N2O6·UO2)2+ complex in pure solvent systems at 25°C decreases in the order: AN>THF>DMF. In the case of binary solvent solutions, the stability constant of the complex at 25°C was found to be: AN–DCM>AN–THF>AN–DMF. The values of thermodynamic quantities (ΔSc°,ΔHc°), for the formation of the complex were obtained from temperature dependence of the stability constant of the complex using the van't Hoff plots. The results show that in all cases, the complex is both entropy and enthalpy stabilized and both of these parameters are affected by the nature and composition of the mixed solvent systems.

Complexation ability of kryptofix 22DD with lanthanum (III) cation in some binary mixed non-aqueous solvents

The complex formation between lanthanum (III) cation with kryptofix 22DD was studied in acetonitrile–dimethylformamide (AN–DMF), acetonitrile–methanol (AN–MeOH), acetonitrile–ethylacetate (AN–EtOAc) and acetonitrile–ethanol (AN–EtOH) binary solvent solutions at different temperatures by using conductometric method. The conductance data show that in all cases, the stoichiometry of the complex formed between the macrocyclic ligand and the metal cation is 1:1 [ML]. The stability order of (kryptofix 22DD.La)3+ complex in the studied binary solvent solutions at 25 °C was found to be: AN–EtOAc>AN–EtOH>AN–MeOH>AN–DMF and in the case of pure non-aqueous solvents at 25 °C was: EtOAc>EtOH>MeOH>AN>DMF. A non-linear behavior was observed for changes of logKf of (kryptofix 22DD.La)3+ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the preferential solvation of the species involved in the complexation reaction. The values of standard thermodynamic parameters (∆H c°, ∆S c°) for formation of (kryptofix 22DD.La)3+ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots.The results show that in most cases, the (kryptofix 22DD.La)3+ complex is enthalpy destabilized, but entropy stabilized and the values of these thermodynamic quantities for formation of the complex are quite sensitive to the nature and composition of the mixed solvents solution.

Study of complexation process between 4′-nitrobenzo-15-crown-5 and yttrium(III) cation in binary mixed non-aqueous solvents using conductometric method

The complexation reaction of macrocyclic ligand (4′-nitrobenzo-15C5) with Y3+ cation was studied in acetonitrile-methanol (AN-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-dimethylformamide (AN-DMF) and ethylacetate-methanol (EtOAc-MeOH) binary mixtures at different temperatures using conductometry method. The conductivity data show that in all solvent systems, the stoichiometry of the complex formed between 4′-nitrobenzo-15C5 and Y3+ cation is 1: 1 (ML). The stability order of (4′-nitrobenzo-15C5). Y3+ complex in pure non-aqueous solvents at 25°C was found to be: EtOAc > EtOH > AN ≈ DMF > MeOH, and in the case of most compositions of the binary mixed solvents at 25°C it was: AN≈MeOH ≈ AN-EtOH > AN-DMF > EtOAc-MeOH. But the results indicate that the sequence of the stability of the complex in the binary mixed solutions changes with temperature. A non-linear behavior was observed for changes of logKf of (4′-nitrobenzo-15C5 · Y3+) complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent interactions and also the hetero-selective solvation of the species involved in the complexation reaction. The values of thermodynamic parameters (ΔHcℴ and ΔScℴ) for formation of the complex were obtained from temperature dependent of the stability constant using the van′t Hoff plots. The results represent that in most cases, the complex is both enthalpy and entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.

Solvent influence upon complexation of N-phenylaza-15-crown-5 with UO2 2+ cation in binary mixed non-aqueous solvents

The complexation reaction of N-phenylaza-15-crown-5 (PhA15C5) with UO2 2+ cation was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–butanol (AN–BuOH), acetonitrile–dimethylformamide (AN–DMF) and methanol–propylencarbonate (MeOH–PC) binary solutions, at different temperatures by conductometry method. The conductance data show that the stoichiometry of the complex formed between PhA15C5 with UO2 2+ cation in most cases is 1:1 [M:L], but in some solvent systems a 1:2 [M:L2] complex is formed in solutions. The results revealed that, the stability constant of (PhA15C5·UO2)2+ complex in the binary mixed solvents varies in the order: AN–BuOH>AN–MeOH>AN–DMF. In the case of the pure organic solvents, the sequence of the stability of the complex changes as: AN>PC>BuOH>DMF. A non-linear relationship was observed for changes of logKf of (PhA15C5·UO2)2+ complex versus the composition of the binary mixed solvents. The corresponding standard thermodynamic parameters (ΔHc°, ΔSc°) were obtained from temperature dependence of the stability constant. The results show that the values and also the sign of these parameters are influenced by the nature and composition of the mixed solvents.

Solvent Influence upon Complex Formation between Dibenzo-18-crown-6 with the Y3+ Metal Cation in Pure and Binary Mixed Organic Solvents

The complexation reaction between the Y3+ cation with the macrocyclic ligand dibenzo-18-crown-6 (DB18C6) was studied in acetonitrile–dimethylformamide (AN-DMF), acetonitrile–ethanol (AN-EtOH), acetonitrile–propanol (AN-PrOH), and dimethylformamide–methanol (DMF-MeOH) binary mixtures at different temperatures using a conductometric method. In all cases, DB18C6 forms a 1:1 complex with the Y3+ cation. The stability order of (DB18C6.Y)3+ complex changes with the composition of the mixed solvents. For example, the stability constant of the complex in the binary mixed solutions with 75 % AN at 25 °C varies in order: AN-EtOH > AN-PrOH ∼ AN-DMF, but in the case of 50 % AN was found to be: AN-DMF > AN-PrOH ∼ AN-EtOH. A nonlinear behavior was observed between the log Kf of the complex versus the composition of the mixed solvents, which may be related to solvent–solvent interactions which result in changing the solvation of the metal cation, ligand, and even the resulting complex in the binary mixed solvents. The values of the standard thermodynamic parameters (ΔS°c, ΔH°c) for formation of the (DB18C6.Y)3+ complex were obtained from the temperature dependence of the formation constant of the complex using van't Hoff plots. The obtained results show that the complexation reaction between DB18C6 with this metal cation in most cases is entropy-destabilized, but from the enthalpy viewpoint, depending on the nature of the medium, the complexation process is enthalpy-stabilized or -destabilized.

Complexing ability of a macrocyclic ligand, dibenzo-24-crown-8, with UO2 2+ in some binary mixed non-aqueous solvents

Complexation between and dibenzo-24-crown-8 (DB24C8) was studied in acetonitrile–ethylacetate (AN–EtOAc), acetonitrile–dimethylformamide (AN–DMF), acetonitrile–methanol (AN–MeOH), acetonitrile–ethanol (AN–EtOH), and acetonitrile–propanol (AN–PrOH) binary solutions at different temperatures using conductometry. The conductance data show that in most cases the stoichiometry of the complex formed between DB24C8 and is 1 : 1 [M : L], but in pure EtOAc, a 1 : 2 [M : L2] complex is formed in the solution. In all cases, except in pure EtOAc, addition of DB24C8 to solutions causes a decrease in molar conductivity which indicates that the mobility of the complexed cation is lesser than that of the uncomplexed one. Non-linear behavior was observed for the changes of log K f of (DB24C8 · UO2)2+ versus the composition of the binary mixed solvents. The stability order of the complex in binary mixed solvents at 25°C was: AN–EtOAc > AN–PrOH ∼ AN–EtOH ∼ AN–MeOH > AN–DMF. The standard thermodynamic quantities ( and ) for the formation of (DB24C8 · UO2)2+ were obtained from the temperature dependence of the stability constant using van't Hoff plots. The results show that in most cases complexation between and DB24C8 is enthalpy and entropy stabilized and the values of these thermodynamic parameters are influenced by the nature and composition of the mixed solvents.

Effect of solvent on the stability constant of complex formation and the thermodynamic parameters between dicyclohexyl-18-crown-6 with Eu3+, La3+, Er3+ and Y3+ cations

The complexation reaction between Eu3+, La3+, Er3+ and Y3+ cations with the dicyclohexyl-18-crown-6 (DCH18C6) in acetonitrile (AN)–dimethylformamide (DMF) and AN–methanol (MeOH) binary systems have been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1:1 [ML]. The results show that the stability constant of complexes in various solvents is: AN > MeOH > DMF. In the some cases, the minimum of logKf for (DCH18C6–Eu3+), (DCH18C6–La3+), (DCH18C6–Er3+) and (DCH18C6–Y3+) complexes in AN–MeOH binary systems obtain at χMeOH ~ 0.75, and also, the logKf of (DCH18C6–Er3+) complex in AN–DMF binary systems show a minimum at χAN ~ 0.75. Non-linear behavior was observed for the stability constant of complexes versus the composition of the solvent systems. The experimental data show that the selectivity order of DCH18C6 for these cations in AN–MeOH binary systems (mol% AN = 50, 75) at 25 °C is: Y3+ > Er3+ > Eu3+ > La3+. The values of thermodynamic parameters (∆H˚C) for formation of complexes were obtained from temperature dependence of stability constants of complexes using the van′t Hoff plots and the standard entropy (∆S˚C) were calculated from the relationship: ∆G˚C, 298.15 = ∆H˚C −298.15∆S˚C. The results show that the values of these thermodynamic parameters are influenced by the nature and the composition of the binary systems.

Complex Formation of 1,10-Dibenzyl-1,10-diaza-18-crown-6 with Ni2+, Cu2+, Ag+ and Cd2+ Metal Cations in Acetonitrile–dimethylformamide Binary Solutions

Conductance measurements are reported for nickel(II), cupper(II), silver(I) and cadmium(II), salts in acetonitrile (AN)–dimethylformamide (DMF) binary solvents containing macrocyclic ligand, 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBDA18C6) at different temperatures. The changes in molar conductance caused by addition of DBDA18C6 to solutions were analyzed by non-linear least squares to give stability constants of 1:1 metal cation–DBDA18C6 complexes. The results show that the stabilities of the complexes are sensitive to solvent composition and in some cases the sequence of stabilities is changed with changing the composition of the mixed solvents. The values of thermodynamic quantities (ΔH°c and ΔS°c) for formation of DBDA18C6-Ni2+, DBDA18C6-Cu2+, DBDA18C6-Ag+ and DBDA18C6-Cd2+ complexes were obtained from temperature dependence of the stability constants and the results show that the values of ΔH°c and ΔS°c for these complexes are sensitive to the nature and composition of AN–DMF binary solutions, but they do not vary monotonically with the solvent composition.

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.

FT-Raman spectroscopic evidences for the preferential solvation of sodium tetrafluorobrate in acetonitrile-based mixed solvents

Solutions of sodium tetrafluorobrate in acetonitrile–dimethylformamide, and acetonitrile–dimethylsulfoxide mixtures have been studied by FT-Raman spectroscopy for three solvent compositions, respectively. New bands due to solvent molecules in the first solvation shell of Na + were detected in the region of the O C N deformation and CH 3 rocking mode for amide and of the S O and C S stretching modes for sulfoxide. The individual solvation numbers of sodium cation in different environment were deduced. In all the cases, it is found that the sodium ion was preferentially solvated by DMF or DMSO in respective binary solvents. This result was further supported by ab initio calculations.