Cl-AGGREGATES IN CRYSTALS OF DICHLORO-NAPHTHALENES AND CHLOROBENZENE. I. Neretin, P.M. Zorky. Department of Chemistry, Moscow State University, Moscow 119899, Russia

The halogene atoms form as usual some aggregates (layers, ribbons) in organic crystals; the examples of such aggregates have been described in the previous works of P.M. Zorky. Each Hal atom has four or five nearest neighbours in such formations, and the mean distance Hal...Hal is approximately equal to double vdw radius (2R_vdw).

In this work the Cl-aggregates in crystals of 2,6-dichloronaphthalene (I), 1,4 -dichloronaphthalene (II) and chlorobenzene (III) are considered. In all of them each Cl atom forms as usual two contacts Cl...Cl which are shorter then 2R_vdw=3.80Å and two contacts Cl...Cl which are rather longer then 2R_vdw.

The existence of Cl-layers has been found in a,b and g forms of dichlorobenzene. It was interesting to know what a change of crystal structure occurs in substances with a smaller concentration of Cl. There are two ways of decreasing of Cl concentration: 1) increasing of the carbon part of a molecule, 2) decreasing of the number of Cl atoms. The first of them takes place in I and II; the ribbons of Cl atoms exist in these crystals. The second way is realized in III, where the roads formed by Cl atoms occur.