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The phase transitions of 4‐aminopyridine‐based indolocarbazoles: twinning, local‐ and pseudo‐symmetry
Author(s) -
Kader Thomas,
Stöger Berthold,
Fröhlich Johannes,
Kautny Paul
Publication year - 2019
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520618017341
Subject(s) - crystal twinning , crystallography , crystal structure , phase transition , polymorphism (computer science) , atom (system on chip) , chemistry , space group , group (periodic table) , materials science , diffraction , condensed matter physics , x ray crystallography , physics , biochemistry , microstructure , computer science , genotype , embedded system , gene , organic chemistry , optics
The phase transitions and polymorphism of three 4‐aminopyridine‐based indolocarbazole analogues are analyzed with respect to symmetry relationships and twinning. Seven polymorphs were structurally characterized using single‐crystal diffraction. 5NICz (the indolo[3,2,1‐ jk ]carbazole derivative with the C atom in the 5‐position replaced by N) crystallizes as a P 2 1 / a high‐temperature (270 K) polymorph and as a Pca 2 1 low‐temperature (150 K) polymorph. Even though their space‐group symmetry is not related by a group–subgroup relationship, the local symmetries of both belong to the same order–disorder (OD) groupoid family. Both are polytypes of a maximum degree of order and are twinned by point operations of the other polytype. 2NICz (C atom in the 2‐position replaced by N) likewise crystallizes in a high‐temperature ( Pcca , 280 K) polymorph and a low‐temperature ( P 2 1 / c , 150 K) polymorph. Here, the space‐group symmetries are related by a group–subgroup relationship. The low‐temperature phase is twinned by the point operations lost on cooling. The crystal structure of bulk 2,5NICz (N‐substitution at the 2‐ and 5‐positions) was unrelated to 2NICz and 5NICz and no phase transition was observed. Isolated single crystals of a different polymorph of 2,5NICz, isotypic with 2NICz, were isolated. However, the analogous phase transition in this case takes place at distinctly higher temperatures (> 300 K).