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The structures and phase transitions in 4‐aminopyridinium tetraaquabis(sulfato)iron(III), (C 5 H 7 N 2 )[Fe III (H 2 O) 4 (SO 4 ) 2 ]
Author(s) -
Bednarchuk Tamara J.,
Hornfeck Wolfgang,
Kinzhybalo Vasyl,
Zhou Zhengyang,
Dušek Michal,
Pietraszko Adam
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/s2052520619013155
Subject(s) - crystallography , triclinic crystal system , monoclinic crystal system , chemistry , crystal structure , phase transition , atmospheric temperature range , octahedron , differential scanning calorimetry , crystal twinning , diffraction , physics , thermodynamics , microstructure , optics
The organic–inorganic hybrid compound 4‐aminopyridinium tetraaquabis(sulfato)iron(III), (C 5 H 7 N 2 )[Fe III (H 2 O) 4 (SO 4 ) 2 ] (4apFeS), was obtained by slow evaporation of the solvent at room temperature and characterized by single‐crystal X‐ray diffraction in the temperature range from 290 to 80 K. Differential scanning calorimetry revealed that the title compound undergoes a sequence of three reversible phase transitions, which has been verified by variable‐temperature X‐ray diffraction analysis during cooling–heating cycles over the temperature ranges 290–100–290 K. In the room‐temperature phase (I), space group C 2/ c , oxygen atoms from the closest Fe‐atom environment (octahedral) were disordered over two equivalent positions around a twofold axis. Two intermediate phases (II), (III) were solved and refined as incommensurately modulated structures, employing the superspace formalism applied to single‐crystal X‐ray diffraction data. Both structures can be described in the (3+1)‐dimensional monoclinic X 2/ c (α,0,γ)0 s superspace group (where X is ½, ½, 0, ½) with modulation wavevectors q = (0.2943, 0, 0.5640) and q = (0.3366, 0, 0.5544) for phases (II) and (III), respectively. The completely ordered low‐temperature phase (IV) was refined with the twinning model in the triclinic P space group, revealing the existence of two domains. The dynamics of the disordered anionic substructure in the 4apFeS crystal seems to play an essential role in the phase transition mechanisms. The discrete organic moieties were found to be fully ordered even at room temperature.