(2-Bromoethyl)trimethylammonium bromide and thiourea: A comparative study of three crystal structures

The crystal structures of the ionic compounds [(CH3)3NCH2CH2Br]Br (1) and [(CH3)3NCH2CH2SC(NH2)2]Br2 (2) as well as the reaction product of 1 with thiourea, [(CH3)3NCH2CH2SC(NH2)2]Br2·4(NH2)2CS (2·4 thiourea) have been determined by single-crystal X-ray diffraction, 273 K for 1 and 2·4 thiourea, 296 K for 2. Crystal data: 1, space group P21, a = 7.207(2) Å, b = 8.475(2) Å, c = 7.433(2) Å, β = 108.56(3)°, Z = 2, R1 = 0.0646 and wR2 = 0.1598; 2, space group P21/c, a = 11.782(1) Å, b = 9.365(1) Å, c = 11.689(1) Å, β = 107.63(1)°, Z = 4, R1 = 0.0249 and wR2 = 0.0527, 2·4 thiourea, space group P1¯, a = 9.309(2) Å, b = 9.557(2) Å, c = 16.520(3) Å, α = 102.20(3)°, β = 100.79(3)°, γ = 104.18(3)°, Z = 2, R1 = 0.0230 and wR2 = 0.0563. In 1, short distances between ions of opposite charge allow for favourable lattice energy; in addition, non-classical C-H···Br interactions and Br···Br contacts occur. In 2, each N-H donor finds an accepting bromide in suitable geometry: N-H···Br bonds account for the most relevant contacts in this solid. 2·4 thiourea represents a tetrathiourea solvate of the previous structure; packing of the constituents is dominated by classical hydrogen bonding involving N-H as donor and S or Br− as acceptor groups. The compound can be understood as an anionic host lattice of thiourea molecules and bromide anions which accommodates the isothiuronium cations in the resulting channels.