The hydration numbers and thermal properties of tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrate crystals formed from TBAB aqueous solutions with TBAB mole fractions (x) in the range of (0.0060-0.0360) were investigated by ion chromatography and differential scanning calorimetry (DSC). The hydration numbers of TBAB hydrates can be estimated from combined ion chromatography and DSC. The hydration number (n) and dissociation enthalpy of orthorhombic TBAB hydrate are constant at n = 38 and Delta H-diss approximate to 220 kJ mol(-1), respectively, for x = (0.0060-0.0120). The hydration numbers and the enthalpies of tetragonal TBAB hydrates gradually increase from n = 26.0 and Delta H-diss = 149 kJ mol(-1) at x = 0.0360 to n = 28.2 and Delta H-diss= 160 kJ mol(-1) at x = 0.0150, respectively. The dissociation enthalpies of tetragonal TBAB hydrates linearly increase from n = (26 to 32), which indicates that the enthalpies increase because of an increasing number of hydrogen bonds forming the TBAB hydrates. The dissociation temperatures of tetragonal TBAB hydrates decrease with increasing hydration number, and crystals with higher hydration numbers are thermodynamically unstable. (C) 2018 Elsevier Ltd.