Isostructural and Nonisostructural Compounds in Series of Halogenated Organic Crystal Substances. Structure of Hal-Aggregates

The local characteristics and the form of intermolecular Hal aggregates (assemblies of contacting halogen atoms of neighboring molecules), existing in haloorganic crystal substances differing only in the nature of Hal atoms, are compared. Twenty three series of halogenated hydrocarbons involving 57 crystal structures are considered. Pronounced specifics of Hal-aggregates has been established for compounds with low and medium halogen contents. It is found that k(Hal) (coordination number of the Hal atom with respect to the neighboring Hal atoms) generally increases in the series F–Cl–Br–I; for constant k(Hal), <> = i - 2R_Hal> nearly always decreases (r_i is the distance from the Hal atom in question to one of the k nearest Hal atoms, and R_Hal is the van der Waals radius).