| Abstract
| - The molecular dipole moment of MNA in the crystal has been critically reexamined, to test the conclusionfrom an earlier experimental charge density analysis that it was substantially enhanced due to a combinationof strong intermolecular interactions and crystal field effects. X-ray and neutron diffraction data have beencarefully measured at 100 K and supplemented with ab initio crystal Hartree−Fock calculations. Considerablecare taken in the measurement and reduction of the experimental data excluded most systematic errors, andsources of error and their effects on the experimental electron density have been carefully investigated. Theelectron density derived from a fit to theoretical structure factors assisted in the determination of the scaleand thermal motion model. The dipole moment enhancement for MNA in the crystal is much less than thatreported previously and only on the order of 30−40% (∼2.5 D). In addition to the dipole moment, experimentaldeformation electron density maps, bond critical point data, electric field gradients at hydrogen nuclei, andatomic and group charges all agree well with theoretical results and trends. Anisotropic modeling of themotion of hydrogen atoms, integral use of periodic ab initio calculations, and improved data quality are allaspects of this study that represent a considerable advance over previous work.
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