calixarenes and cesium-fluoride

Theoretical studies of a new ion-pair receptor, meso-octamethylcalix[4]pyrrole (OMCP), and its interactions with the halide anions F(-), Cl(-), and Br(-) and the cesium halides CsF, CsCl, and CsBr have been performed. Geometries, binding energies, and binding enthalpies were evaluated with the restricted hybrid Becke three-parameter exchange functional (B3LYP) method using the 6-31+G(d) basis set and relativistic effective core potentials. The optimized geometric structures were used to perform natural bond orbital (NBO) analysis. The two typical types of hydrogen bonds, N-H…X(-) and C-H…X(-), were investigated. The results indicate that hydrogen bonding interactions are dominant, and that the halide anions (F(-), Cl(-), and Br(-)) offer lone pair electrons to the σ*(N-H) or σ*(C-H) antibonding orbitals of OMCP. In addition, electrostatic interactions between the lone pair electrons of the halide anion and the LP* orbitals of Cs(+) as well as cation-π interactions between the metal ion and π-orbitals of the pyrrole rings have important roles to play in the Cs(+)•OMCP•X(-) complexes. The current study further demonstrates that this easy-to-make OMCP host compound functions as not only an anion receptor but also an ion-pair receptor.

Topics: Algorithms; Bromides; Calixarenes; Cesium; Chlorides; Computer Simulation; Coordination Complexes; Fluorides; Hydrogen Bonding; Models, Molecular; Molecular Conformation; Porphyrins; Quantum Theory; Thermodynamics

An ion-pair receptor, 1, containing both cation- and anion-recognizing sites, has been synthesized and characterized. Single-crystal X-ray diffraction structural studies and (1)H NMR spectroscopic analyses confirmed that 1 forms stable 1:1 complexes with CsF in solution and in the solid state in spite of the large separation enforced between the receptor-bound anion and cation. In 9:1 CDCl3/CD3OD, binding of fluoride anion within the calix[4]pyrrole core of 1 was not observed in the absence of a cobound cesium cation; however, it was seen in this solvent mixture under conditions where a Cs(+) cation was bound to the crown ether-strapped calix[4]arene subunit.

Topics: Calixarenes; Cesium; Crown Ethers; Crystallography, X-Ray; Fluorides; Ions; Magnetic Resonance Spectroscopy; Phenols; Porphyrins