ELECTRON CRYSTALLOGRAPHY OF SMALL ORGANIC-MOLECULES - CRITERIA FOR DATA-COLLECTION AND STRATEGIES FOR STRUCTURE SOLUTION

By crystallization onto an organic substrate such as naphthalene, thin microcrystals of a small organic molecule, such as triphenylene, can be grown. These crystals are less perturbed by shear and erratic bend disorder than the samples produced by rapid growth from dilute solutio ns. Selected-area electron diffraction intensities are consistent from specimen to specimen, show the symmetry expected for the crystalline projection and, furthermore, correspond to the Fourier transform of th e entire unit cell. However, undersampling of the three-dimensional re ciprocal lattice by goniometry can frustrate structure determination i f conventional direct methods are used. Nevertheless, the crystal stru cture may still be solved quite accurately by energy minimization.