Anomalous Dielectric Behavior and Thermal Motion of Water Molecules Confined in Channels of Porous Coordination Polymer Crystals

Guest water molecules confined in channels of porous coordination polymer crystals [Ln₂Cu₃(IDA)₆]·nH₂O (Ln = La, Nd, Sm, Gd, Ho, Er; IDA = [NH(CH₂COO)₂]²⁻; n ≈ 9) exhibited large dielectric constants (ε) and antiferroelectric behaviors at high temperatures (e.g., ε(Sm) ≈ 1300 at 400 K). In addition, plots of the temperature dependence of ε showed broad peaks at ∼170 K, below which ε became very small. These puzzling temperature dependences of ε are consistent with the results of molecular dynamics simulations, suggesting the “freezing of thermal motion” of water molecules at ∼170 K.