Crystal structure, phase transitions and vibrational spectra of bis(betaine) nitrate

Abstract

The crystal structure of bis(betaine) nitrate (BBN) has been determined by X-ray diffraction as monoclinic, space group P2 1/ c, with a = 5.668(1), b = 11.259(2) and c = 23.073(5) Å, β = 93.65(3)°, Z = 4. The crystal comprises nitrate ions, NO 3 −, and betaine dimers: two betaine moieties are joined by a very strong asymmetric hydrogen bond with an O···O distance of 2.449(2) Å. Fist order type phase transitions at 394 K, 439 K and 460 K (melting and decomposition) and very likely second order type at about 448 K were discovered for the BBN sample by the Differential Scanning Calorimetry method. In the deuterated analogue they appear at 394 K, 434 K, 448 K and 459 K. The FTIR and FT-Raman spectra for the powder samples were measured at room temperature. Additionally the FTIR spectra were taken at low temperatures (till 10 K). A strong band at about 900 cm −1 arises from the ν aOHO vibration of the very strong hydrogen bond. The site symmetry of the NO 3 − anions is C 1 according to X-ray data and the vibrational spectra.