Emanuel Makrlík

Contribution to the thermodynamics of complexes of alkali metal cations with dibenzo-18-crown-6 in water-nitrobenzene extraction system

Constantes de stabilite des complexes ML + dans le nitrobenzene. Evaluation des constantes dextraction

Interaction of Cesium Ions with Calix[4]arene-bis(t-octylbenzo-18-crown-6): NMR and Theoretical Study

Using (1)H, (13)C, and (133)Cs NMR spectra, it is shown that calix[4]arene-bis(t-octylbenzo-18-crown-6) (L) forms complexes with one (L·Cs(+)) and two (L·2Cs(+)) Cs(+) ions offered by cesium bis(1,2-dicarbollide) cobaltate (CsDCC) in nitrobenzene-d(5). The ions interact with all six oxygen atoms in the crown-ether ring and the π electrons of the calixarene aromatic moieties. According to extraction technique, the stability constant of the first complex is log β(nb)(L·Cs(+)) = 8.8 ± 0.1. According to (133)Cs NMR spectra, the value of the equilibrium constant of the second complex is log K(nb)((2))(L·2Cs(+)) = 6.3 ± 0.2, i.e., its stabilization constant is log β(nb)(L·2Cs(+)) = 15.1 ± 0.3. Self-diffusion measurements by (1)H pulsed-field gradient (PFG) NMR combined with density functional theory (DFT) calculations suggest that one DCC(–) ion is tightly associated with L·Cs(+), decreasing its positive charge and consequently stabilizing the second complex, L·2Cs(+). Using a saturation-transfer (133)Cs NMR technique, the correlation times τ(ex) of chemical exchange between L·Cs(+) and L·2Cs(+) as well as between L·2Cs(+) and free Cs(+) ions were determined as 33.6 and 29.2 ms, respectively.

Interaction of Hydrated Protons with Trioctylphosphine Oxide: NMR and Theoretical Study

Interaction of trioctylphosphine oxide (TOPO) with fully ionized hydrated protons (HP) was studied in acetonitrile-d(3) and nitrobenzene-d(5) using (1)H, (13)C, and (31)P NMR, PFG NMR, and magnetic relaxation, and the experimental results were confronted with high-precision ab initio DFT calculations. Relative chemical shifts of NMR signals of TOPO (0.02 mol/L) under the presence of HP in the molar ratio beta = 0-2.0 mol/mol show binding between TOPO and HP. Self-diffusion measurements using (1)H PFG NMR demonstrate that larger complexes with higher content of TOPO are generally formed at beta < 0.75. Analyzing the dependence of (31)P NMR chemical shifts on beta by the use of program LETAGROP, we obtained very good fitting for the assumed coexistence of three complexes (TOPO)(i).HP (named C(i)), where i = 1, 2, 3. The logarithms of the respective stabilization constants log K(i) were found to be 3.63, 4.67, and 7.23 in acetonitrile and 3.91, 6.04, and 7.92 in nitrobenzene. The (31)P NMR chemical shifts Deltadelta(i) corresponding to these complexes are 39.35, 29.51, and 19.72 ppm in acetonitrile and 38.37, 28.47, and 18.63 ppm in nitrobenzene. These values and the calculated values of alpha(i) =[C(i)]/[TOPO](0) were utilized in the analysis of the system dynamics. This was done by measuring the transverse (31)P NMR relaxation by the CPMG sequence with varying delays t(p) between the pi pulses in the mixtures with beta = 0.5, 1.25, and 1.5. Calculating the probabilities of imaginable exchange processes shows that only three of them can have significant influence on relaxation rate R(2), namely C(1) <--> TOPO, C(2) <--> C(1), and C(3) <--> C(2). Using the slopes of the R(2)-t(p)(-1) dependences in the above three mixtures, the following correlation times were obtained: tau(10) = 2.5 x 10(-6), tau(21) = 7.4 x 10(-5), tau(32) = 11.3 x 10(-5) s. The DFT calculations support the hypothesis that complexes C(1) to C(3) are the main species in the mixtures of TOPO with HP, with the only exception that additional water molecules are bound to the complexes in the case of C(1) and C(2). Schematically, the compositions of the three stable complexes is [3TOPO.H(3)O](+), [2TOPO.H(3)O.H(2)O](+), and [TOPO.H(3)O.2H(2)O](+). The relative (31)P NMR shifts calculated for the optimized structures of C(1), C(2), and C(3) are in very good agreement with the experimentally observed values.

CONTRIBUTION TO THE THERMODYNAMICS OF COMPLEXES OF ALKALI METAL CATIONS WITH 18-CROWN-6 IN THE WATER - NITROBENZENE EXTRACTION SYSTEM

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+NaL+(nb)⇄ML+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (M+=Li+, K+, Rb+, Cs+; L=18-crown-6; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. The stability constants of the ML+ complexes in nitrobenzene saturated with water were calculated; they are found to increase in the cation order Cs+Li+Na+Rb+K+. Further, the individual extraction constants for the NaL+, KL+, RbL+ and CsL+ complex species in the wate-nitrobenzene system were determined; their values increase in the series Na+Rb+Cs+K+.

Stability of complex of Cs+ with valinomycin in nitrobenzene saturated with water

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the equilibrium Cs+(aq)+Cl−(aq)+L(nb)⇆CsL+(nb)+Cl−(nb) in the two-phase water-nitrobenzene system (L=valinomycin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as log Kex(CsL+, Cl−)=2.2. Further, the stability constant of the valinomycin-cesium complex in nitrobenzene saturated with water was calculated: log βnb(Csl+)=10.1.

Extraction of Microamounts of Calcium and Strontium into Nitrobenzene by Using Hydrogen Dicarbollylcobaltate in the Presence of “Classical” CMPO

Abstract Extraction of microamounts of calcium and strontium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of octyl-phenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide (“classical” CMPO, L) has been investigated. The equilibrium data have been explained assuming that the complexes HL+, HL2+, CaL2+, CaL22+, CaL32+, SrL22+, SrL32+ and SrL42+ are extracted into the organic phase. The values of extraction and stability constants of the species in nitrobenzene saturated with water have been determined.

Stability and Probable Structure of Protonatedp-tert-Butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide)

Abstract From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H3O+(aq) + 1 · Na+(nb) ↔ 1 · H3O+ (nb) + Na+(aq) taking place in the two-phase water-nitrobenzene system (1 = p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (H3O+,1 · Na+) = –0.4±0.1. Moreover, the stability constant of the 1 · H3O+ complex in water saturated nitrobenzene was calculated for a temperature of 25 °C as log βnb (1 · H3O+) = 5.5±0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1 · H3O+ complex species was derived. In this complex, the hydroxonium ion H3O+ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygens of 1 by strong hydrogen bonds and other electrostatic interactions.

Contribution to the Complexation of some Univalent Metal Cations with p-Tert-Butylcalix[4]arene-Tetrakis(N,N-Diethylacetamide) in Nitrobenzene Saturated with Water

Abstract From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M+(aq)+NaL+(nb)⇔ML+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (M+=Li+, Ag+, Rb+, Tl+, Cs+; L=p-tert-butylcalix[4]arene-tetrakis(N,N-diethylacetamide); aq=aqueous phase, nb=nitrobenzene phase) were determined. Moreover, the stability constants of the ML+ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Cs+ < Rb+ < Tl+ < Ag+ < Li+.

Individual extraction constants of some dicarbollylcobaltate anions in the water-nitrobenzene system

Individual extraction constants of nine dicarbollylcobaltate anions in the two-phase water-nitrobenzene system were determined radiometrically assuming that the changes of Gibbs energy of the transfer of the tetraphenylarsonium cation, Ph4As+, and of the tetraphenylborate anion, BPh4−, from the aqueous into the nitrobenzene phase are equal. The constants obtained by this method were correlated with Hanschs constants of hydrophobity.

Protonation of Benzo-18-crown-6: Extraction and DFT Study

Abstract From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H3O+(aq) + 1·Na+(nb)⇌1·H3O+(nb) + Na+(aq) taking place in the two-phase water-nitrobenzene system (1 = benzo-18-crown-6, aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex(H3O+, 1·Na+)=-0.8±0.1. Further, the stability constant of the 1·H3O+ complex in water-saturated nitrobenzene was calculated for a temperature of 25°C as log βnb(1·H3O+)=6.3±0.1. Finally, by using quantum mechanical DFT calculations, the most probable structure of the 1·H3O+ cationic complex species was derived. In this complex, the hydroxonium ion H3O+ is bound by three strong linear hydrogen bonds to one (Ar–O–CH2) ethereal oxygen and two (CH2–O–CH2) ethereal oxygen atoms of the parent crown ligand 1. The interaction energy was found to be -401.4kJ/mol, confirming the formation of the considered complex 1·H3O+.