Naslov
An Integrated Approach (Thermodynamic, Structural and Computational) to the Study of Complexation of Alkali-Metal Cations by a Lower-Rim Calix[4]arene Amide Derivative in Acetonitrile

Autori
Horvat, Gordan ; Stilinović, Vladimir ; Hrenar, Tomica ; Kaitner, Branko ; Frkanec, Leo ; Tomišić, Vladislav

Izvornik
Inorganic chemistry (0020-1669) 51 (2012), 11; 6264-6278

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
calixarenes ; cations ; supramolecular chemistry ; structure elucidation ; computational chemistry

Sažetak
The calix[4]arene secondary-amide derivative L was synthesized and its complexation with alkali metal cations in acetonitrile was studied by means of spectrophotometric, NMR, conductometric and microcalorimetric titrations at 25 °C. The stability constants of the 1:1 (metal:ligand) complexes determined by different methods were in excellent agreement. For the complexation of M+ (M = Li, Na, K) with L, both enthalpic and entropic contributions were favorable, with their values and mutual relations being quite strongly dependent on the cation. The enthalpic and overall stability was the largest in the case of sodium complex. Molecular and crystal structures of free L, its methanol and acetonitrile solvates, sodium complex and its acetonitrile solvate were determined by single crystal X-ray diffraction. The inclusion of acetonitrile molecule into the calixarene hydrophobic cavity was observed both in solution and in the solid state. This specific interaction was found to be stronger in the case of metal complexes compared to free ligand due to the better preorganization of the hydrophobic cone to accept the solvent molecule. DFT calculations showed that the flattened cone conformation (C2 point group) of L was generally more favorable than the square cone conformation (C4 point group). In the complex with Na+, L was in square cone conformation whereas in its adduct with acetonitrile the conformation was slightly distorted from the full symmetry. These conformations were in agreement with those observed in the solid state. The classical molecular dynamics simulations indicated that acetonitrile molecule enters the L hydrophobic cavity of both free ligand and its alkali metal complexes. The inclusion of MeCN into the cone of free L was accompanied by the conformational change from C2 to C4 symmetry. As in solution studies, in the case of ML+ complexes an allosteric effect was observed: the ligand was already in the appropriate square cone conformation to bind the solvent molecule, allowing it to more easily and faster enter the calixarene cavity.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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