References

X-ray powder diffraction patterns were obtained with an automatic Philips diffractometer (Nifiltered CuKα radiation). Conformational and packing energy energy calculations were performed with the software package CERIUS 1 using the force field PCFF. For the conformational energy calculations on isolated molecules, a cut-off distance of 4 Å for attractive nonbonded interactions and for Coulombic interactions (dielectric constant, ε =1) was selected, and a spline function was used from 4 to 5 Å to attenuate gradually the interaction energy from its full value to zero. No interactions over 5 Å was taken into account. A direct comparison between the experimental X-ray powder diffraction profile and the calculated intensities was obtained calculating the X-ray powder diffraction profile (Icalc,2θi) from the calculated structure factors Fhkl of the hkl reflections: