PREDICTING X-RAY-DIFFRACTION INTENSITY DISTRIBUTIONS FOR ONE-DIMENSIONAL INCLUSION-COMPOUNDS VIA LOCAL-DENSITY FUNCTIONAL CALCULATIONS

We investigate whether certain features of the X-ray diffraction (XRD) pattern arising from the guest molecules in one-dimensional inclusion compounds can be predicted and rationalized on the basis of the elect ron-density distribution computed for the periodic guest structure in the inclusion compound. Specifically, we note that in the XRD patterns of diacyl peroxide/urea inclusion compounds, scattering in reciprocal lattice planes (hkl)g with odd I is significantly more intense than t hat in the adjacent reciprocal lattice planes with even I, whereas for alkane/urea inclusion compounds there is a monotonic decrease in inte nsity as I is increased. Local density functional methods have been us ed to compute the electron-density distributions for the guest structu res in the dioctanoyl peroxide/urea and decane/urea inclusion compound s; and the methodology required to use this information to calculate t he XRD intensities 1(hkl)g , as a function of I index, is described. I t is demonstrated that XRD intensity distributions derived from the co mputed guest electron densities do indeed predict correctly the contra sting relationships between 1(hkl)g and I, observed experimentally, fo r the diacyl peroxide/urea and alkane/urea inclusion compounds.