An Ab Initio Investigation of the Structure and Alkali Metal Cation Selectivity of 18-Crown-6

We present an ab inito, quantum mechanical study of 18-crown-6 (18c6) and its interaction with the alkali metal cations Li[sup +], Na[sup +], K[sup +], Rb[sup +], and Cs[sup +]. Geometries, binding energies, and binding enthalpies are evaluated at the restricted Hartree-Fock (RHF) level using standa...

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Bibliographic Details
Published in:Journal of the American Chemical Society 1994-11, Vol.116 (23), p.10657-10669
Main Authors: Glendening, Eric D, Feller, David, Thompson, Mark A
Format: Article
Language:English
Subjects:
400201 - Chemical & Physicochemical Properties
990200 - Mathematics & Computers
ALKALI METAL COMPOUNDS
CALCULATION METHODS
CHARGE TRANSPORT
CHEMICAL BONDS
CHEMICAL REACTIONS
CROWN ETHERS
ELECTRONIC STRUCTURE
ENTHALPY
ETHERS
FUNCTIONS
GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
HARTREE-FOCK METHOD
HYDRATION
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
MECHANICS
MOLECULAR ORBITAL METHOD
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
QUANTUM MECHANICS
SOLVATION
THERMODYNAMIC PROPERTIES
WAVE FUNCTIONS
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Summary:We present an ab inito, quantum mechanical study of 18-crown-6 (18c6) and its interaction with the alkali metal cations Li[sup +], Na[sup +], K[sup +], Rb[sup +], and Cs[sup +]. Geometries, binding energies, and binding enthalpies are evaluated at the restricted Hartree-Fock (RHF) level using standard basis sets (3-21G and 6-31 + G*) and relativistic effective core potentials. Electron correlation effects are determined at the MP2 level, and wave function analysis is performed by the natural bond orbital (NBO) and associated methods. The affinity of 18c6 for the alkali metal cations is quite strong (50-100 kcal mol[sup [minus]1], depending on cation type), arising largely from the electrostatic (ionic) interaction of the cation with the nucleophilic ether backbone. Charge transfer (covalent bonding) contributions are somewhat less important, only 20-50% as strong as the electrostatic interaction. Agreement of the calculated binding enthalpies and experimentally determined quantities is rather poor. For example, the binding energy for K[sup +]/18c6 (-71.5 kcal mol[sup [minus]1]) is about 30 kcal mol[sup [minus]1] stronger than that determined by experiment, and it is not clear how to reconcile this difference. Our calculations clearly show that solvation effects strongly influence cation selectivity. 48 refs., 12 figs., 5 tabs.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja00102a035