Dielectric anomaly and giant deuteration effect in a H-bond trimeric co-crystal [4, 4'-Bipyridine]₂[1,4-dihydroxybenzene]

Co-crystal [4,4ʹ-bipyridine]2[1,4-dihydroxybenzene] (1) was prepared by evaporating methanol solution of 4,4ʹ-bipyridine with 1,4-dihydroxybenzene at 4°C. 1 shows a fascinating dielectric anomaly with a maximum at ~210 K, which is independent on ac frequency. However, the absence of thermal anomaly and structural phase transition is related to the dielectric anomaly. The co-crystal [4,4ʹ-bipyridine]2[1,4-dihydroxybenzene-d2] (2) was further obtained via H+/D+ exchange in 1 and the deuteration gives rise to the maximum shifting to 254 K in the dielectric spectrum of 2. The dielectric anomaly corresponds to disorder-to-order transformation of H+/D+ in the O–H/D···N H-bond in 1 and 2.