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We placed nanometer-scale water-tube clusters with phase transition within a porous crystal formed from molecular blocks specifically designed to investigate the molecular dynamics of confined water molecules.

The unique strength, directionality, and complementarity of noncovalent interactions such as hydrogen bonding and coordination bonding play a central role in the creation of a variety of molecular architectures for molecular self-assembly and recognition in chemical, physical, and biological sciences. [1, 2] The building blocks possessing such noncovalent interaction sites can produce one-, two-, and three-dimensional molecular arrangements with long-range order. [3±5] Control of such multidimensional molecular arrangements is essential for progressing crystal engineering and in constructing the desired molecular-based materials. [6±8] We have designed a new anionic building block, a tris(biimidazolato)nickel(ii) complex, in which the three strong, p-conjugated biimidazolate ligands each provide one complementary hydrogen-bonding site. We now report the construction of four types of hydrogen-bonded and coordination-bonded molecular architectures of nickel(ii) ions, biimidazolate ligands, and counter cations.Since 2,2'-biimidazole (H 2 bim) is a bidentate chelating ligand with multiple proton-donor sites, it can coordinate to a transition metal in three reversible protonated and deprotonated modes: neutral (H 2 bim), monoanionic (Hbim À1 ), and dianionic (bim À2 ). [9] The mono-deprotonated ligand (Hbim À1 ) can form both a complementary binary NH´´´N-type hydrogen bond and a coordination bond with metal ions (see structure A). [10] In this study, we have found that simple one-pot procedures [11] of mixing the nickel(ii) ions, Hbim À1 , and counter cations produces four types of hydrogen-bonded crystals (1 ± 4) based on arrangements of the [Ni(Hbim) 3 ] À building blocks ( Figure 1). Figures 2 and 3 show the schematic drawings and crystal structures of the four types of molecular arrangements. Figure 1. L and D isomers of the building block [Ni(Hbim) 3 ] À . d) expanded 2D honeycomb sheet b) 1D zigzag ribbon c) 2D honeycomb sheet a) 0D dot Figure 2. Schematic representations of the hydrogen-bonded networks of [Ni(Hbim) 3 ] À building blocks for 1 ± 4 (a ± d). Water molecules (*) and free 2,2'-biimidazole (*) also function as intermediate spacers.As a common feature, all the structures contain the anionic building block [Ni(Hbim) 3 ] À , in which the central Ni II atom is coordinated by three bidentate Hbim À ligands through the lone pairs of the imine nitrogen atoms in the imidazole rings. The NiÀN bond lengths are in the range of 1.96(3) ± 2.19(2) . The building block has approximate D 3 symmetry; both the D and L isomers are illustrated in Figure 1.Structure 1 [12a] contains tetramethylammonium as the counter cation (Figures 2 a, 3 a). Although there is no hydrogen bonding between the ligands of the [Ni(Hbim) 3 ] À building blocks, the units are connected by hydrogen bonding through water molecules to make a sheet arrangement along the ab plane (Figure 2 a): The length of the hydrogen bonds between the oxygen atoms of the water molecules and the nitrogen atoms of the Hbim À ligands are 2.753(4) and 2.756(4) ...

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