TY  - JOUR
AU  - Noohinejad, Leila
AU  - Mondal, Swastik
AU  - Wölfel, Alexander
AU  - Ali, Sk Imran
AU  - Schönleber, Andreas
AU  - van Smaalen, Sander
TI  - Ferroelectricity of Phenazine-Chloranilic Acid at T = 100 K
JO  - Journal of chemical crystallography
VL  - 44
IS  - 8
SN  - 1572-8854
CY  - Dordrecht [u.a.]
PB  - Springer Science + Business Media B.V
M1  - PUBDB-2014-04193
SP  - 387 - 393
PY  - 2014
AB  - The co-crystal of phenazine (Phz) and chloroanilic acid (H2ca) is ferroelectric below the temperature TIc=253  K (FE-I phase). Upon cooling, two more phase transitions involve a further reduction of symmetry, until Phz-H 2 ca is triclinic in the second ferroelectric phase (FE-II phase) stable below TIIc=   137 K. Ferroelectricity in all low-temperature phases is believed to be related to partial proton transfer within the hydrogen bonds between the molecules Phz and H2ca . Here we present the crystal structure of the FE-II phase at T=100  K. Experimental positions of hydrogen atoms indicate that ferroelectricity is mainly governed by half of the hydrogen-bonded chains, whereby proton transfer is observed within one of the two hydrogen bonds in which each molecule participates. A simple point charge model quantitatively reproduces the polarisation of this material. However, a possible contribution to the polarisation is proposed of the O–H ⋯ N hydrogen bonds of the second half of the mixed chains, which show elongated O–H bonds similar to those in the FE-I phase. The twofold superstructure with P1 symmetry was successfully solved as commensurately modulated structure employing the monoclinic superspace group P21(1/2σ21/2)0 . The latter shows that the distortions at low temperatures follow a single normal mode of the space group P21 of the FE-I phase, and it thus explains that the direction of the polarisation remains close to the monoclinic axis, despite the lowering towards triclinic symmetry
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000340101500001
DO  - DOI:10.1007/s10870-014-0527-1
UR  - https://bib-pubdb1.desy.de/record/192611
ER  -