Predicting X-ray diffraction intensity distributions for one-dimensional inclusion compounds via local density functional calculations

Abstract

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 electron-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 l is significantly more intense than that in the adjacent reciprocal lattice planes with even l, whereas for alkane/urea inclusion compounds there is a monotonic decrease in intensity as l is increased. Local density functional methods have been used to compute the electron-density distributions for the guest structures in the dioctanoyl peroxide/urea and decane/urea inclusion compounds; and the methodology required to use this information to calculate the XRD intensities l(hkl)_g, as a function of l index, is described. It is demonstrated that XRD intensity distributions derived from the computed guest electron densities do indeed predict correctly the contrasting relationships between l(hkl)_g and l, observed experimentally, for the diacyl peroxide/urea and alkane/urea inclusion compounds.