Encapsulation of Water Cluster, meso-Helical Chain and Tapes in Metal−Organic Frameworks Based on Double-Stranded Cd(II) Helicates and Carboxylates

Four new complexes [Cd4(bpa)2(MeCO2)8]·9H2O (1), {[Cd4(bpa)4(suc)2(H2O)4](suc)2·17H2O}n (2), {[Cd2(bpa)2(glu)2]·9H2O}n (3), and {[Cd2(bpa)2(adi)2]·11H2O}n (4) (where bpa = N,N‘-bis(picolinamide)azine, H2suc = succinic acid, H2glu = glutaric acid, and H2adi = adipic acid) have been synthesized by the reactions of the bpa ligand and different Cd(II) carboxylates in similar conditions. Their structures consist of double-stranded helical [Cd2(bpa)2] structural units and various carboxylates. Each of the [Cd2(bpa)2] structural units in 1 is capped at its both ends by acetate-chelated Cd(II) fragments through acetate bridges into discrete tetranuclear species, which are self-assembled into two-dimensional (2D) hydrogen-bonded sheets with cavities. The 2D hydrogen-bonded sheets in 1 are threaded by one-dimensional (1D) water tapes featuring (H2O)4 clusters to generate an unprecedented three-dimensional (3D) hydrogen-bonded polypseudo-rotaxane architecture. The [Cd2(bpa)2] structural units as secondary building b...