The crystal structure of β-quinol clathrate was investigated by empirical force-field calculations using two sets of potential functions—AMBER and CVFF. The crystal was approximated by the fragments containing 3402 and 15 750 quinol atoms. It was shown that the AMBER potentials are more precise when describing the experimental data on structure of β-quinol clathrate. The bond stretching, valence angle and out-of-plane bendings, dihedral torsion, van der Waals and electrostatic interactions, and hydrogen bonding were taken into account in the potential energy U. The contribution of each of these energies to the formation of structure was estimated. The energy U was minimized with respect to the independent coordinates of the lattice, unit-cell parameters, and both translation and orientation parameters of included molecules. The equilibrium states of encaged guest molecules, β-quinol lattice structure, and energy of clathrate formation were determined for 27 encaged guest molecules. It was shown that the β-quinol lattice can contract as well as expand depending on the type of an encaged molecule. The distribution of charges around the cage favors the positively charged atoms of the molecule to be located in the center of a cage, in contrast with those negatively charged which occupy the sites in the vicinity of peripheral hydroxyl hexagons. The electrostatic component of guest–guest interaction strongly affects the equilibrium position of guest molecules with large dipole moment. Quantitative estimates of various structural and energetic characteristics for β-quinol clathrate prove to be in good agreement with experimental data.

Articles you may be interested inComputersimulation studies of βquinol clathrate with various gases. Molecular interactions and crystal structure J. Chem. Phys. 97, 8617 (1992); 10.1063/1.463380 A theoretical study of the inclusion complexes of βquinol J. Chem. Phys. 89, 968 (1988); 10.1063/1.455166Translational motions of raregas atoms, rotationtranslation motions of diatomic molecules, and host-guest interactions in βquinol clathrateThe equilibrium crystal structure of a ,8-quinol clathrate occupied by various gases is determined through empirical force field calculations. The guests with van der Waals volume V m ~ 27 cm 3 fmol affect the structure and rigidity of the lattice in a manner independent of their chemical nature: The guest-host attraction leads to a shrinking of the host cages. On the other hand, the inclusion of molecules of the volume 27 cm3fmol~V m:S;;46 cm 3 fmol expands the cages. Guest molecules render the host lattice more rigid, except for large spherical rotor type molecules; which soften the lattice, eventually destroying it The inclusion of molecules with V m>46 cm 3 /mol is likely to be impossible. The energy of clathrate formation increases with increasing V m' with the polar guests forming more stable clathrates than the nonpolar ones with the same V m • Interestingly, the optimal guest-cage compatibility occurs when the volume of guest molecules differs by less than 50% from the volume of the empty cage. The orientation of a guest molecule in a cage is mainly determined by a competition of three types of interactions. (i) Van der Waals interactions tend to direct the long axis of the guests along the c-axis of the cage. (ii) The electrostatic guest-host interaction tends to place a positively charged guest atom into the center of the cage. (iii) Electrostatic guest-guest interactions tend to align the dipole moments of the included molecules along the c-axis. The different orientations are'rationalized in terms of the complementary influences of the guest size, guest polarity and an "atomic size" factor. The calculated barriers hindering the reorientation movement of guest molecules in a cage are found to be in a qualitative agreement with experimental data except for the N2 and CO molecules, which are supposed to be considerably polarized by the cage. The Crreorientation motion of ethane is predicted to be accompanied by its synchronous rotation around the C-C bond.

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