Triglycine sulfate

Triglycine sulfate

Names
IUPAC name Glycine sulfate (3:1)
Other names Glycine sulfate; TGS
Identifiers
CAS Registry Number	513-29-1 Y
ChemSpider	10111
InChI InChI=1S/3C2H5NO2.H2O4S/c3*3-1-2(4)5;1-5(2,3)4/h3*1,3H2,(H,4,5);(H2,1,2,3,4)
Jmol-3D images	Image
PubChem	10551
SMILES O=C(O)CN.O=S(=O)(O)O.O=C(O)CN.O=C(O)CN
Properties
Molecular formula	C6H17N3O10S
Molar mass	323.28 g·mol−1
Appearance	White powder
Density	1.69 g/cm3[1]
Structure
Crystal structure	Monoclinic
Space group	P21[2]
Lattice constant	a = 0.9417 nm, b = 1.2643 nm, c = 0.5735 nm
Lattice constant	α = 90°, β = 110°, γ = 90°
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Triglycine sulfate (TGS) is a chemical compound with a formula (NH₂CH₂COOH)₃·H₂SO₄. The empirical formula of TGS does not represent the molecular structure, which contains protonated glycine moieties and sulfate ions. TGS with protons replaced by deuterium is called deuterated TGS or DTGS; alternatively, DTGS may refer to doped TGS. TGS and DTGS crystals are pyroelectric and ferroelectric and have been used as detector elements in infrared spectroscopy.

Crystal structure and properties

Crystal structure of TGS. Hydrogen atoms are not shown.^[2]

TGS crystals may be formed by evaporation of an aqueous solution of sulfuric acid, which is containing a greater than three-fold excess of glycine.^[3] They belong to the polar space group P2₁ and therefore are pyroelectric and ferroelectric at room temperature, exhibiting spontaneous polarization along the b-axis ([010] direction). The Curie temperature of the ferroelectric transition is 49 °C for TGS and 62 °C for DTGS. The crystal structure consists of SO₄²⁻, 2(N⁺H₃CH₂COOH) (G1 and G2 in the crystal-structure diagram), and N⁺H₃CH₂COO⁻ (G3) species held together by hydrogen bonds.^[4] These bonds are easily broken by the polar molecules of water that explains the hygroscopicity of TGS – its crystals are easily etched by water. Along the b-axis, the G1-SO₄ and G2-G3 layers are stacked alternately. The nearest two neighboring layers with identical chemical composition are rotated 180° around the b-axis against each other.^[2][5]

References