Abstract
Water confined to the quasi-one-dimensional hydrophilic molecular nanoporous crystal of {[Co(II)(H(2)bim)(3)](TMA)·20H(2)O}(n) (1) (H(2)bim = 2,2'-biimidazole, TMA(3-) = trimesate) forms dynamic water molecule clusters (WMCs) with a hierarchical three-layered hydrogen-bonding (H-bonding) structure and a time-averaged structure in the melting state due to interactions with the walls of the ∼1.6 nm nanopores. This was first revealed by measuring the solid-state (2)H NMR spectra of a single crystal of {[Co(III)(D(2)bim)(3)](TMA)·20D(2)O}(n) (1'), which revealed distinct hierarchical peaks of H(2)O H-bonding interactions. In addition, the frozen WMCs in 1 exhibit a premelting state, retaining some ice structures, just before melting through a first-order phase transition during the heating process. Measurements of the spin-lattice relaxation time (T(1)) in solid-state (2)H NMR revealed rapid rotation motions for water molecules in these premelting WMCs, resulting in a correlation time τ closer to that of bulk liquid water.