Structure Analysis of Modulated Molecular Crystals IV: Survey of our Recent Studies

摘要: There has been a considerable upsurge in interest modulated crystal following the development of multidimensional description solids by DeWolff, Janner and Janssen1,2,3. Modulations are quite common minerals inorganic 4 which often exhibit substitutional displacive modulations at or above ambient temperatures. However, with greater awareness occurrence wider accessibility low temperature diffraction equipment suitable for routine use, number known molecular is rapidly increasing. Among most thoroughly studied low-temperature phase biphenyl5,6,7 thiourea, stable over narrow range between 202 169K (ref. 8). Table 1 lists some solids. In almost all studies have made, atoms molecule treated as individual entities, rather than parts rigid covalently bonded framework. Since this can lead to unlikely distortions geometry, we introduced model displacement each atom determined not its own location, but point group, referred reference point9. The displacements described terms rigid-body translations rotations, thus greatly reducing parameters model. A harmonic general requires twelve per molecule, be from usually large measurable satellite reflections.