Crystal structure, properties and phase transitions of morpholinium tetrafluoroborate [C4H10NO][BF4]

The crystal structure of [C4H10NO][BF4] is determined in the phase I at 160, 180, 240 and 290 K. At room temperature the compound crystallizes in the orthorhombic space group: Pnam. The structure is composed of the morpholinium cations, [C4H10NO]+, which form one-dimensional hydrogen bonded chains, and [BF4]− anions. [C4H10NO][BF4] undergoes two structural phase transformations: second-order at 153 K and first-order at 117/118 K (cooling/heating). The phase transitions are characterized with the differential scanning calorimetry, dilatometric and dielectric techniques. The possible mechanism of the phase transitions in [C4H10NO][BF4] is discussed on the basis of the presented results.