Abstract
Precise single-crystal structure analyses of the title compound, bis-(glycinium) sulfate-glycine (1/1), 2C2H6NO2 +·SO4 2-·C2H5NO2 (or C6H17N3O10S), non-deuterated triglycine sulfate (HTGS) at 20 K and 298 K were undertaken using time-of-flight neutron diffraction data. At 20 K for the O-H⋯O hydrogen bond between the glycinium cation and the zwitterionic, unprotonated glycine mol-ecule that is associated with the ferroelectric behaviour of HTGS, O-H = 1.070 (3), H⋯O = 1.408 (3) [δ = 0.338 (4)], O⋯O = 2.4777 (15) Å and O-H⋯O = 179.0 (4)°, which is in good agreement with previous studies. Two reasonable structures for the same three atoms were refined for the 298 K dataset. One is a single-minimum potential-energy model, with O-H = 1.090 (12), H⋯O = 1.361 (12) [δ = 0.271 (17)], O⋯O = 2.450 (7) Å and O-H⋯O = 179.2 (10)°, having the H atom with a large ellipticity along the bond path between the O atoms. The other is a double-minimum potential-energy model having two H atom sites with occupancies of 0.876 (8) and 0.124 (8): for the major occupancy component, O-H = 1.065 (12), H⋯O = 1.387 (12), O⋯O = 2.451 (7) Å and O-H⋯O = 178.2 (11)° and for the minor component, O-H = 1.06 (4), H⋯O = 1.41 (4), O⋯O = 2.451 (7) Å and O-H⋯O = 166 (2)°. These models did not show any significant differences in R factors. In addition, the unit-cell parameters and other structural parameters of HTGS did not show any major differences compared to those of partially deuterated TGS and fully deuterated TGS for both 20 K and 298 K.
Highlights
Triglycine sulfate, 2(C2H6NO2)+Á(C2H5NO2)Á(SO4)2– (TGS), is a hydrogen-bond ferroelectric material (Matthias et al 1956) exhibiting a second-order and order–disorder-type ferroelectric phase transition at a Curie temperature (TC) of 322 K (Triebwasser, 1958)
The authors proposed a hydrogen-bonding scheme and pointed out that the hydrogen atom that lies between the oxygen atom of the carboxyl group in the glycine III cation (GIII) and the O atom in the glycine II molecule (GII) plays a crucial role in the dipole reversal
The neutron diffraction experiment revealed that the hydrogen atom forming the O—HÁ Á ÁO hydrogen bond between the GIII and GII species was closer to the GIII O atom compared to that in GII
Summary
Triglycine sulfate, 2(C2H6NO2)+Á(C2H5NO2)Á(SO4)2– (TGS), is a hydrogen-bond ferroelectric material (Matthias et al 1956) exhibiting a second-order and order–disorder-type ferroelectric phase transition at a Curie temperature (TC) of 322 K (Triebwasser, 1958). Crystal-structure refinements of partially deuterated TGS (DTGS), where deuterium replaced the H atoms except for the hydrogen atoms of the methylene (CH2) group in each glycine molecule and those in sulfuric acid molecules at 40 K and 180 K (Protas et al, 1997) showed that the refined structures were consistent with those of the HTGS reported by Kay & Kleinberg (1973). The parameters do not show any major differences, and H15 is 0.338 (4) Acloser to atom O15 in GIII than O3 in GII This result shows good agreement with the data previously reported for DTGS (Protas et al 1997), it may be concluded that the intermolecular distances and angles do not change significantly upon deuteration
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