Single crystal X-ray diffraction study of the cubic ionic clathrate hydrate of tetrabutyl ammonium propionate (C4H9)4NC2H5COO·27.0H2O

Abstract

Single crystal X-ray diffraction is used for the first time to study the structure of the ionic clathrate hydrate of tetrabutyl ammonium propionate (C4H9)4NC2H5COO·27.0H2O with the host framework based on cubic arrangement I. The structural model is characterized by a high degree of disordering in both guest and host subsystems. The structural features indicate a colocation of cations and anions in multicell 4T·nD cavities with n = 0–4; the simplest option is a pairwise location of cations and anions in combined five-cell 4T·D cavities. The positional ordering of cations leads to the formation of a 2×2×2 supercell (space group $$I\bar 43d$$ , a = 24.312(6)A). The resulting model confirms the characteristic features of ionic clathrate hydrates of tetrabutyl and tetraisoamyl ammonium carboxylates. Non-standard refinement techniques are described, which may be of interest for other structures with a high degree of disordering. The proposed structural interpretation can serve as a basis for a further investigation of this class of compounds by other methods.