EXPERIMENTAL CHARGE-DENSITY STUDY ON AN IONIC CROWN-ETHER COMPLEX - [KC18-CROWN-6]N--CENTER-DOT-H2O((3))

The low-temperature (120 K) structure experimental charge density dist ribution and electrostatic potential of the title complex were determi ned from high-resolution X-ray diffraction intensities. The molecular structure and packing is in accord with previous observations on analo gous compounds. The nuclear-centered spherical harmonics expansion tec hnique was applied in the treatment of the data to extract the static electron density. Deformation electron density maps in nonbonded regio ns of the oxygen atoms show lone-pair polarization toward the cation. This valence deformation is compared to that found in the neutral host -guest complex of 18-crown-6.2cyanamide. The anisotropic atomic displa cement parameters are tested against the rigid-body motion model, and the residuals for both structures are analyzed with computer graphics. The degree of transferability in the topology of static density defor mations is examined in connection with the transferability in the patt ern of residual root-mean-square surfaces representing atomic displace ments due to internal motion.