Synthesis,structural phase transition,and characterization of potassium hydrogen bis-dichloroacetate

Potassium hydrogen bis-dichloroacetate (1) was synthesized and separated as crystals. Differential scanning calorimetry (DSC) measurement reveals that this compound undergoes a reversible phase transition at about 259 K with a heat hysteresis of 23.5 K. Dielectric anomaly observed at 260 K in the heating process further confirms the phase transition. The room temperature X-ray single-crystal structure determination indicates that 1 crystallizes in the monoclinic crystal system with a centrosymmetric space group P2₁/c, and cell parameters are a =?6.240(1), b =?23.177(4), c =?7.335(1) Å, β =?106.938(1)°, V =?1014.8(3) ų, and Z =?4. In the low temperature phase, 1 also crystallizes in monolinic with space group P2₁/c, and cell parameters are a =?6.180(1), b =?22.988(2), c =?7.200(1) Å, β =?108.098(1)°, V =?972.4(1) ų, and Z =?4. The structural phase transition is dominating caused by the torsion of bond angles.