Spontaneous Assembly of 6³ Topological Metal−Organic Nanotubes with Distinct Asymmetric Subunits for the Construction of Hydrophilic Intertube Channels Encapsulating Rare Helical Water-Chains

The hydrothermal reaction of cadmium nitrate hydrate (Cd(NO₃)₂·4H₂O) with p-terphenyl-type 4,4′-(1,4-phenylene)bis(2,6-dimethyl-3,5-pyridinedicarboxylic acid) (H₄L), and phenanthroline (phen) in the presence of triethylamine leads to a three-dimensional supramolecular aggregate {[Cd₃(phen)₃(HL)₂(H₂O)₂]·4.25H₂O}_n (1). In 1, the T-type second building units construct independent one-dimensional (1-D) metal−organic nanotubes (MONTs) with 6³ topology containing distinct axially asymmetric subunits [R-Cd₃(HL) and S-Cd₃(HL)]. The adjacent RR-Cd₅(HL)₂ supersubunits form a hydrophilic intertube chiral channel (I), and the SS-Cd₅(HL)₂ supersubunits generate another type of hydrophilic intertube chiral channel (II). These two types of chiral channels encapsulate two corresponding types of helical water-chains with three pseudo screw axes, exhibiting a novel chirality transformation and transfer, namely, R-Cd₃(HL) → RR-Cd₅(HL)₂ → chiral channel (I) → left-handed (M) water-helix, and S-Cd₃(HL) → SS-Cd₅(HL)₂ → chiral channel (II) → right-handed (P) water-helix. Photoluminescence and nitrogen adsorption behavior of 1 have been examined.