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

Co-crystal [4,4’-bipyridine]₂[1,4-dihydroxybenzene] (<b>1</b>) was prepared by evaporating methanol solution of 4, 4’-bipyridine with 1, 4-dihydroxybenzene at 4 °C. <b>1</b> shows a fascinating dielectric anomaly with a maximum at ca. 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 [4,4’-bipyridine]₂[1,4-dihydroxybenzene-d₂] (<b>2</b>) was further obtained via H⁺/D⁺ exchange in <b>1</b> and the deuteration gives rise to the maximum shifting to 254 K in the dielectric spectrum of <b>2</b>. The dielectric anomaly corresponds to disorder-to-order transformation of H⁺/D⁺ in the O-H/D…N H-bond in <b>1</b> and <b>2</b>.