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On crystal chemistry and morphology of extended organic molecules
Author(s) -
Follner H.
Publication year - 1981
Publication title -
kristall und technik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0023-4753
DOI - 10.1002/crat.19810161102
Subject(s) - molecule , symmetry (geometry) , group (periodic table) , crystallography , position (finance) , crystal structure , space (punctuation) , plane symmetry , plane (geometry) , space group , chemistry , crystal (programming language) , symmetry operation , physics , combinatorics , stereochemistry , geometry , mathematics , x ray crystallography , optics , diffraction , quantum mechanics , computer science , programming language , finance , economics , operating system
The present paper is concerned with the morphology and crystal structure of extended organic compounds in the space group P 2 1 /c. In the structures with molecules in general position ( Z = 4) the longitudinal axis of all molecules run parallel to a ( h 0 l )‐plane. The molecule arrangements are based on four different structure types. The planes through the molecule axis contain a) 2 1 ‐axis and symmetry centres ( l = 2 n ), b) 2 1 ‐axis or symmetry centres ( l = 2 n + 1) and c) respectively d) no symmetry element ( l = 2 n resp. 2 n + 1). In the last two cases the net plane distances are to be halved. As in P 2 1 /c the a ‐und c ‐axis are not set, one can confine oneself to the examination of the net planes ( 1 02), ( 2 02), ( 2 04), and ( 4 04). In the cases of a) and b), only certain morphological lattices appear, which distinguish themselves through additional translations in three‐dimensional space resp. in the projections. In the cases of c) and d) there are also found morphological lattices which generate additional “morphological extinctions” (consequently possessing a higher symmetry than the generating space group), but which contain no translationally higher symmetry. ( h 0 l )‐faces, to which the molecule axis run parallel, appear with preference on crystals. As a rule the first two and the last two cases can be differentiated on account of the position of the ( h 0 l )‐faces in the Donnay‐Harker series. Some examples will show that the morphological lattice can be preserved through Fourier transformation of crystal morphology.