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1.
Gholamhossein Rounaghi Roya Mohammad Zade Kakhki 《Journal of inclusion phenomena and macrocyclic chemistry》2009,63(1-2):117-122
In the present work the complexation process between UO2 2+ cation and the macrocyclic ligand, dibenzo-18-crown-6 (DB18C6) was studied in ethylacetate–dimethylformamide (EtOAc/DMF), ethylacetate–acetonitrile (EtOAc/AN), and ethylacetate–tetrahydrofuran (EtOAc/THF) and ethylacetate–propylencarbonate (EtOAc/PC) binary solutions at different temperatures using the conductometric method. The results show that the stoichiometry of the (DB18C6 . UO2)2+ complex in all binary mixed solvents is 1:1. A non-linear behavior was observed for changes of log Kf of this complex versus the composition of the binary mixed solvents. The stability constant of (DB18C6 . UO2)2+ complex in various neat solvents at 25 °C decreases in order: THF > EtOAc > PC > AN > DMF, and in the binary solvents at 25 °C is: THF–EtOAc > PC–EtOAc > DMF–EtOAc ≈ AN–EtOAc. The values of thermodynamic quantities (?H°c, ?S°c) for formation of this complex in the different binary solutions were obtained from temperature dependence of its stability constant and the results show that the thermodynamics of complexation reaction between UO2 2+ cation and DB18C6 is affected strongly by the nature and composition of the mixed solvents. 相似文献
2.
G. H. Rounaghi M. H. Zavar R. Mohammad Zadeh Kakhki 《Russian Journal of Coordination Chemistry》2008,34(3):167-171
The complexation reactions between K+, Ag+, NH4+, and Hg2+ cations and the macrocyclic ligand, dibenzo-18-crown-6 (DB18C6), were studied in ethylacetate (EtOAc)-dimethylformamide (DMF)
binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry
of all the complexes is 1:1. A non-linear behavior was observed for the variation of log K
f
of the complexes versus the composition of binary mixed solvents, which was discussed in terms of heteroselective solvation
and solvent-solvent interactions in binary solutions. It was found that the stability order of the complexes changes with
changing the composition of the mixed solvents. The sequence of stabilities for the K+, Ag+, NH4+, and Hg2+ complexes with DB18C6 in EtOAc-DMF binary solutions (mol. % DMF 25.0) and (mol. % DMF 50.0) at 25°C is (DB18C6-Ag)+ > (DB18C6-K)+ > (DB18C6-Hg)2+ > (DB18C6-NH4)+, but in the cases of pure DMF and a binary solution of EtOAc-DMF (mol. % DMF 75.0) is (DB18C6-K)+ > (DB18C6-Hg)2+ > (DB18C6-Ag)+ ≈ (DB18C6-NH4)+. The values of thermodynamic quantities (ΔH
c
o, ΔS
c
o) for these complexation reactions have been determined from the temperature dependence of the stability constants, and the
results show that the thermodynamics of the complexation reactions is affected by the nature and composition of the mixed
solvents and, in all cases, positive values of ΔS
c
o characterize the formation of these complexes. In addition, the experimental results show that the values of entropies for
the complexation reactions between K+, Ag+, NH4+, and Hg2+ cations and DB18C6 in EtOAc-DMF binary solutions do not change monotonically with the solvent composition.
The text was submitted by the authors in English. 相似文献
3.
The complexation reactions between the Tl+ ion and large crown ethers dibenzo-30-crown-10 (DB30C10), dibenzo-27-crown-9 (DB27C9), dibenzo-24-crown-8 (DB24C8) and dibenzo-21-crown-7 (DB21C7) were studied in different acetonitrile-water mixtures at 25°C using an a.c. polarographic technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in peak potential of the polarographic waves of the metal ion against the crown concentration. In all solvent mixtures used, the stability of the resulting 1:1 complexes was found to vary in the order DC24C8 » DB30C10 > DB21C7 > DB27C9 > DB24C8. There is an inverse relationship between the complex formation constants and the amount of water in the mixed solvent. In all cases, a linear relation was observed between log Kf and the mole fraction of acetonitrile in its mixtures with water. 相似文献
4.
Gholam Hossein Rounaghi Azadeh Shafaie Bejestani Mahmoud Chamsaz 《Journal of inclusion phenomena and macrocyclic chemistry》2013,77(1-4):395-402
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. 相似文献
5.
Fahimeh Razghandi Gholamhossein Rounaghi Roya Mohammadzadeh Kakhki 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):279-286
The complexation reaction of macrocyclic ligand, dibenzo-18-crown-6 (DB18C6) with UO2 2+ cation was studied in ethylacetate-1,2-dichloroethane (EtOAc/DCE), acetonitrile-1,2-dichloroethane (AN/DCE), methanol-1,2-dichloroethane (MeOH/DCE) and ethanol-1,2-dichloroethane (EtOH/DCE) binary solutions at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complex formed between DB18C6 and UO2 2+ cation is affected by the nature of the solvent systems. A non-linear behaviour was observed for changes of log K f of (DB18C6.UO2)+2 complex versus the composition of the binary mixed solvents. The values of thermodynamic quantities (?S°c, ?H°c) for formation of (DB18C6.UO2)+2 complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases, the complex is enthalpy stabilized and in all cases entropy stabilized and both parameters are affected by the nature and composition of the mixed solvents. In addition, the complex formation between dicyclohexyl-18-crown-6 (DCH18C6) and UO2 2+ cation was studied in pure AN and the results were compared with those of the (DB18C6.UO2)+2 complex. 相似文献
6.
Gholam Hossein Rounaghi Bahareh Nouri Somayeh Tarahomi 《Journal of inclusion phenomena and macrocyclic chemistry》2012,72(3-4):331-338
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. 相似文献
7.
N. Habibi G. H. Rounaghi M. Mohajeri 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2012,86(13):2018-2023
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 logK f 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 (??H c ? and ??S c ? ) 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. 相似文献
8.
Gholam Hossein Rounaghi Mohammad Hossein Arbab Zavvar Azam Saremi 《Russian Journal of Inorganic Chemistry》2007,52(1):134-140
The complexation reactions between alkali and alkaline-earth metal cations with DB18C6 were studied in acetonitrile-methanol
(AN-MeOH) and tetrahydrofuran-threechloromethane (THF-CHCl3) binary mixtures at different temperatures using the conductometric method. The obtained results show that in most cases,
the DB18C6 forms 1:1 complexes with these metal cations and the stability of the complexes is affected by the nature and composition
of the mixed solvents. The stability order of complexes in AN-MeOH binary systems was found to be Na+ > Li+, and in the case of THF-CHCl3 binary mixtures was Na+ > Ba2+ > Li+. An anomalous and interesting behavior was observed for the case of complexation of a K+ ion with DB18C6 in the AN-MeOH binary
mixture and also for complexation of Mg2+ and Ca2+ cations with this ligand in pure THF and also in THF-CHCl3 binary systems. The values of the thermodynamic parameters (ΔH
c
o
and ΔS
c
o
) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that
the complexes are both enthalpy-and entropy-stabilized.
The text was submitted by the authors in English. 相似文献
9.
M. Ansari Fard G. H. Rounaghi M. Chamsaz K. Taheri 《Journal of inclusion phenomena and macrocyclic chemistry》2009,64(1-2):49-56
The complexation reaction between UO2 2+ cation with macrocyclic ligand, 18-crown-6 (18C6), was studied in acetonitrile–methanol (AN–MeOH), nitromethane–methanol (NM–MeOH) and propylencarbonate–ethanol (PC–EtOH) binary mixed systems at 25 °C. In addition, the complexation process between UO2 2+ cation with diaza-18-crown-6 (DA18C6) was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–ethanol (AN–EtOH), acetonitrile–ethylacetate (AN–EtOAc), methanol–water (MeOH–H2O), ethanol–water (EtOH–H2O), acetonitrile–water (AN–H2O), dimethylformamide–methanol (DMF–MeOH), dimethylformamide–ethanol (DMF–EtOH), and dimethylformamide–ethylacetate (DMF–EtOAc) binary solutions at 25 °C using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between (18C6) and (DA18C6) with UO2 2+ cation in most cases is 1:1 [M:L], but in some solvent 1:2 [M:L2] complex is formed in solutions. The values of stability constants (log Kf) of (18C6 · UO2 2+) and (DA18C6 · UO2 2+) complexes which were obtained from conductometric data, show that the nature and also the composition of the solvent systems are important factors that are effective on the stability and even the stoichiometry of the complexes formed in solutions. In all cases, a non-linear relationship is observed for the changes of stability constants (log Kf) of the (18C6 · UO2 2+) and (DA18C6 · UO2 2+) complexes versus the composition of the binary mixed solvents. The stability order of (18C6 · UO2 2+) complex in pure studied solvents was found to be: EtOH > AN ≈ NM > PC ≈ MeOH, but in the case of (DA18C6 · UO2 2+) complex it was : H2O > MeOH > EtOH. 相似文献
10.
Formation constants of Li+ complexes with 4-substituted dibenzo-14-crown-4 (DB14C4; 4-substituted group: methyl-, tert-butyl-, H-, bromo-, chloro-, formyl-, nitro-) ligands were determined by 7Li NMR spectrometry for solutions in nitromethane (NM), acetonitrile (ACN), propylene carbonate (PC), acetone (AC), Pyridine (Py), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and N,N′-dimethyl formamide (DMF). Only a 1:1 complex was formed in solvents with a small or medium donor number. The formation constants of these complexes are strongly influenced by the size of the metal ion – the effect of the size of the cavity, by the solvent and by substituent. The stability of lithium ion with different substituents on DB14C4 decreases in the order methyl- > tert-butyl- > H- > bromo- > chloro- > formyl- > nitro- in various solvents. A good Hammett correlation was found by plotting log Kf vs. ∑σ in PC and AC. The extent of the substituent effect increases as the donor number of solvent decreases. The complexes were both enthalpy and entropy stabilized. The same magnitude of ΔS° value for different substituents indicates formation with a similar configuration upon complexation between crown ether and lithium ion. A slight variation in entropy contribution was observable depending on the nature of the alkyl substituent, whereas a large variation in enthalpic contribution shows a remarkable substituent effect upon complexation; the effect can reach 70% in magnitude. 相似文献
11.
Razieh Sanavi Khoshnood Elaheh Hatami Donya Arefi Fatemeh Zahra Maknoni 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(2):308-317
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 . 相似文献
12.
Gholam Hossein Rounaghi Behjat Deiminiat Somayeh Tarahomi 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):67-73
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. 相似文献
13.
Mohammad Kazem Rofouei Mehdi Taghdiri Mojtaba Shamsipur 《Journal of inclusion phenomena and macrocyclic chemistry》2008,62(3-4):231-237
The complexation reactions between dicyclohexano-24-crown-8 (DC24C8) and K+, Rb+, Cs+ and Tl+ ions were studied conductometrically in the 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 order of Tl+ > K+ > Rb+ ~ Cs+. The enthalpy and entropy changes of the complexation reactions were evaluated by the temperature dependence of formation constants. It was found that the stability of the resulting complexes increased with increasing nitromethane in the solvent mixture. 相似文献
14.
Mehdi Taghdiri Mohammad Kazem Rofouei Mojtaba Shamsipur 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):181-186
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. 相似文献
15.
Gholamhossein Rounaghi Ali Sarafraz Yazdi Zahra Monsef 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(3-4):231-237
The complexes of Tl+, Pb2+ and Cd2+ cations with the macrocyclic ligand, dicyclohexano-18-crown-6\linebreak(DC18C6) were studied in water/methanol (H2+O/MeOH), water/1-propanol (H2+O/1-PrOH), water/acetonitrile (H2+O/AN), water/dimethylformamide (H2+O/DMF), dimethylformamide/acetonitrile (DMF/AN), dimethylformamide/methanol (DMF/MeOH), dimethylformamide/1-propanol (DMF/1-PrOH) and dimethylformamide/nitromethane (DMF/NM) mixed solvents at 22 °C using differential pulse polarography (DPP), square wave polarography and conductometry. In general, the stability of the complexes was found to decrease with increasing concentration of water in aqueous/non-aqueous mixed solvents with an inverse relationship between the stability constants of the complexes and the concentration of DMF in non-aqueous mixed solvents. The results show that the change in stability of DC18C6.Tl+, vs the composition of solvent in DMF/AN and DMF/NM mixed solvents is apparently different from that in DMF/MeOH and DMF/1-PrOH mixed solvents. While the variation of stability constants of the DC18C6.Tl+ and DC18C6.Pb2+ complexes vs the composition of H2+O/AN mixed solvents is monotonic, an anomalous behavior was observed for variations of log Kf vs the composition of H2+O/1-PrOH and H2+O/MeOH mixed solvents. The selectivity order of the DC18C6 ligand for the cations was found to be Pb2+ > Tl+ > Cd2+. 相似文献
16.
Gholam Hossein Rounaghi Behjat Deiminiat 《Journal of inclusion phenomena and macrocyclic chemistry》2012,72(1-2):113-119
The complexation reaction between Y3+ cation with N-phenylaza-15-crown-5(Ph-N15C5) was studied at different temperatures in acetonitrile–methanol (AN/MeOH), acetonitrile–propanol (AN/PrOH), acetonitrile–1,2 dichloroethane (AN/DCE) and acetonitrile–water (AN/H2O) binary mixtures using the conductometric method. The results show that in all cases, the stoichiometry of the complex is 1:1 (ML). The values of formation constant of the complex which were determined using conductometric data, show that the stability of (Ph-N15C5.Y)3+ complex in pure solvents at 25?°C changes in the following order: PrOH?>?AN?>?MeOH and in the case of binary mixed solutions at 25?°C it follows the order: AN–DCE?>?AN–PrOH?>?AN–MeOH?>?AN–H2O. The values of standard thermodynamic quantities (?H c ° and ?S c ° ) for formation of (Ph-N15C5.Y)3+ complex were obtained from temperature dependence of the formation constant using the van’t Hoff plots. The results show that in most cases, the complex is entropy and enthalpy stabilized and these parameters are influenced by the nature and composition of the mixed solvents. In most cases, a non-linear behavior was observed for variation of log Kf of the complex versus the composition of the binary mixed solvents. In all cases, an enthalpy–entropy compensation effect was observed for formation of (Ph-N15C5.Y)3+ complex in the binary mixed solvents. 相似文献
17.
M. S. Kazemi 《Journal of inclusion phenomena and macrocyclic chemistry》2010,68(3-4):331-338
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. 相似文献
18.
G.H. Rounaghi G.N. Gerey M.S. Kazemi 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):167-172
The complex formation between Cu2+, Zn2+, Tl+ and Cd2+ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K
f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl+ > Cu2+ > Zn2+ > Cd2+ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°C) were calculated from the relationship: ΔG°C,298.15=ΔH°C − 298.15 ΔS°C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°C and ΔS°C depend strongly on the nature of the medium. 相似文献
19.
Mohammad Kazem Rofouei Mehdi Taghdiri Mojtaba Shamsipur Kamal Alizadeh 《Journal of solution chemistry》2010,39(9):1350-1359
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. 相似文献
20.
Stability constants K
ML for the 1:1 complexes of Na+, K+, Rb+, and Cs+ with dibenzo-24-crown-8 (DB24C8) and dibenzo-18-crown-6 (DB18C6) in water have been determined by a capillary electrophoretic technique at 25°C. The K
ML sequence is Na+ < K+ < Rb+ < Cs+ for DB24C8 and Na+ < K+ > Rb+ > Cs+ for DB18C6. Compared with DB18C6, DB24C8 exhibits higher selectivity for K+ over Na+, but lower selectivity for K+, Rb+, and Cs+. To evaluate the solvation of the complexes in water, their transfer activity coefficients sH2O between polar nonaqueous solvents and water have been calculated. The sH2O values provide the following information: interactions with water of the metal ions and of the crown-ether oxygens are greatly reduced upon complexation and the complexes undergo hydrophobic hydration in water; the character of each alkali metal ion in solvation is more effectively masked by DB24C8 than by DB18C6, because of the larger and more flexible ring structure of DB24C8. Solvent effects on the complex stabilities are discussed on the basis of the sH2O values. 相似文献