Two-step dielectric anomalies coupled with structural phase transitions in a co-crystal of 1,4-diazabicyclo[2.2.2]octane and 4,4′-biphenol

The co-crystal of 4,4′-biphenol with 1,4-diazabicyclo[2.2.2]octane (1) was obtained using a mutual diffusion approach of a two component methanol solution at ambient temperature. DSC measurement detected that 1 undergoes two reversible phase transitions at 182 K/167 K and 236 K/229 K in a heating/cooling cycle. The phases are named: high-temperature (HT), intermediate (IT) and low-temperature (LT) ones in descending order of temperature. Each reversible phase transition corresponds to a dielectric anomaly. The single crystal structure analysis revealed that an isostructural phase transition occurs between the HT and IT phases while a symmetry-breaking structural phase transition undergoes between the IT and LT phases. This journal is