Temperature-induced isosymmetric reversible structural phase transition in triethylbenzylammonium perchlorate

The triethylbenzylammonium perchlorate, C13H22N+·ClO4− was synthesized and separated as block colorless crystals. DSC measurement detected that this compound undergoes a reversible phase transition at ca. 196 K with a hysteresis of 18 K width. Dielectric measurements also confirm the transition. The crystal structures determined at 93(2) K (a = 12.114(4)Å, b = 14.320(5)Å, c = 16.418(6)Å, V = 2848.0(17)Å3, Z = 8) and 291(2) K (a = 8.3891(17)Å, b = 12.300(1)Å, c = 14.513(1)Å, V = 1497.5(3) Å3, Z = 4) show that the phase transition is a type of isosymmetric change with the space group of Pbca (No. 61) in the low-temperature phase (LTP) to the space group of Pbcm (No. 57) in the room-temperature phase (RTP). The distinct difference between the LTP and the RTP structure is the different orientation for the anions and the H-bond interactions between the perchlorate anions and triethylbenzylammonium cations. Hydrogen bond interactions may play a role in the phase transition as shown by the changes in the hydrogen bonding pattern as the temperature decreased. The order–disorder type transition of the anions is probably the driving force of the phase transition.