Article

Interaction of hydronium ion with dibenzo-18-crown-6: NMR, IR, and theoretical study.

Institute of Macromolecular Chemistry AS CR, v. v. i., Heyrovskeho Sq. 2, 162 06 Prague, Czech Republic.
The Journal of Physical Chemistry A (Impact Factor: 2.77). 10/2008; 112(41):10236-43. DOI: 10.1021/jp805757d
Source: PubMed

ABSTRACT Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.

0 Bookmarks
 · 
68 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag+ (aq) + 1·Cs+(org) ⇔ 1·Ag+ (org) + Cs+ (aq) taking place in the two-phase water–phenyltrifluoromethyl sulfone (FS 13) system (1 = calix[4]arene-bis(t-octylbenzo-18-crown-6); aq = aqueous phase, org = FS 13 phase) was evaluated as logK ex (Ag+, 1·Cs+) = −1.5 ± 0.1. Further, the stability constant of the 1·Ag+ complex in FS 13 saturated with water was calculated for a temperature of 25 °C: log β org(1·Ag+) = 10.1 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Ag+ was derived. In the resulting 1·Ag+ complex, the “central” cation Ag+ is bound by eight bond interactions to six oxygen atoms from the respective 18-crown-6 moiety and to two carbons of the corresponding two benzene rings of the parent ligand 1 via cation-π interaction.
    Journal of Radioanalytical and Nuclear Chemistry 01/2013; · 1.41 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: From extraction experiments and $ \gamma $ -activity measurements, the extraction constant corresponding to the equilibrium $ {\text{Eu}}^{ 3+ } \left( {\text{aq}} \right) + 3 {\text{A}}^{ - } \left( {\text{aq}} \right) + {\mathbf{1}}\left( {\text{nb}} \right) \Leftrightarrow {\mathbf{1}} \cdot {\text{Eu}}^{ 3+ } \left( {\text{nb}} \right) + 3 {\text{A}}^{ - } \left( {\text{nb}} \right) $ taking place in the two-phase water–nitrobenzene system ( $ {\text{A}}^{ - } = \text {CF}_{3} \text{SO}_{3}^{ - } $ ; 1 = macrocyclic lactam receptor—see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as $ { \log } K_{{{\text{ex}} }} ({\mathbf{1}} \cdot {\text{Eu}}^{ 3+ } ,{\text{ 3A}}^{ - } )\; = \; - 4. 9 \pm 0. 1 $ . Further, the stability constant of the 1·Eu3+ cationic complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: $ { \log } \beta_{{{\text{nb}} }} ({\mathbf{1}} \cdot {\text{Eu}}^{ 3+ } ) \; = \; 8. 2 \pm 0. 1 $ . Finally, using DFT calculations, the most probable structure of the cationic complex species 1·Eu3+ was derived. In the resulting 1·Eu3+ complex, the “central” cation Eu3+ is bound by five bond interactions to two ethereal oxygen atoms and two carbonyl oxygens, as well as to one carbon atom of the corresponding benzene ring of the parent macrocyclic lactam receptor 1 via cation-π interaction. Scheme 1 Structural formula of 2,20-dichloro-9,10,11,12,13,14-hexahydro-6H,22H-dibenzo[n,q][1,4,10,13]dioxadiaza-meta-xylyl-7,15(8H,16H)-dione (abbrev. 1)
    Structural Chemistry 01/2013; · 1.77 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Microstructure of dibenzo-18-crown-6 (DB18C6) and DB18C6/Li(+) complex in different solvents (water, methanol, chloroform, and nitrobenzene) have been analyzed using radial distribution function (RDF), coordination number (CN), and orientation profiles, in order to identify the role of solvents on complexation of DB18C6 with Li(+), using molecular dynamics (MD) simulations. In contrast to aqueous solution of LiCl, no clear solvation pattern is found around Li(+) in the presence of DB18C6. The effect of DB18C6 has been visualized in terms of reduction in peak height and shift in peak positions of gLi-Ow. The appearance of damped oscillations in velocity autocorrelation function (VACF) of complexed Li(+) described the high frequency motion to a "rattling" of the ion in the cage of DB18C6. The solvent-complex interaction is found to be higher for water and methanol due to hydrogen bond (HB) interactions with DB18C6. However, the stability of DB18C6/Li(+) complex is found to be almost similar for each solvent due to weak complex-solvent interactions. Further, Li(+) complex of DB18C6 at the liquid/liquid interface of two immiscible solvents confirm the high interfacial activity of DB18C6 and DB18C6/Li(+) complex. The complexed Li(+) shows higher affinity for water than organic solvents; still they remain at the interface rather than migrating toward water due to higher surface tension of water as compared to organic solvents. These simulation results shed light on the role of counter-ions and spatial orientation of species in pure and hybrid solvents in the complexation of DB18C6 with Li(+).
    Journal of Molecular Modeling 09/2014; 20(9):2413. · 1.98 Impact Factor