Is electron crystallography possible? The direct determination of organic crystal structures

Abstract

When electron diffraction or image data are used to determine organic crystal structures, the analyses are generally carried out with great caution for fear that any of many possible perturbations to the observed intensity will lead these determinations astray. That these data may be analyzed with greater confidence than previously suspected is demonstrated in this paper which describes the successful use of direct phase determination of representative organic structures typically investigated by electron crystallographers, viz.: “small” molecules (urea, thiourea), ring molecules (diketopiperazine, copper perchlorophthalocyanine), linear molecules (paraffins, phospholipids), and linear polymers (polyethylene, and two polyesters). In many cases, three-dimensional determinations are based solely on the probabilistic estimate of three- and four-phase structure invariants, but an important role for high resolution, low dose electron microscope images is also seen in some cases. Electron crystallography, therefore, is a valid technique for quantitative ab initio structure analysis.