Single-crystal structure analysis of non-deuterated triglycine sulfate by neutron diffraction at 20 and 298†K: a new disorder model for the 298†K structure.

Precise single-crystal structure analyses of the title compound, bis-(glycinium) sulfate-glycine (1/1), 2C(2)H(6)NO(2) (+)·SO(4) (2-)·C(2)H(5)NO(2) (or C(6)H(17)N(3)O(10)S), 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)†à 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)†à 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)†à 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)†à 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.