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

Abstract

Four new complexes [Cd 4 (bpa) 2 (MeCO 2 ) 8 ]‚9H 2 O (1), {[Cd 4 (bpa) 4 (suc) 2 (H 2 O) 4 ](suc) 2 ‚17H 2 O} n (2), {[Cd 2 (bpa) 2 (glu) 2 ]‚ 9H 2 O} n (3), and {[Cd 2 (bpa) 2 (adi) 2 ]‚11H 2 O} n (4) (where bpa ) N,N′-bis(picolinamide)azine, H 2 suc ) succinic acid, H 2 glu ) glutaric acid, and H 2 adi ) 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 [Cd 2 (bpa) 2 ] structural units and various carboxylates. Each of the [Cd 2 (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 hydrogenbonded sheets in 1 are threaded by one-dimensional (1D) water tapes featuring (H 2 O) 4 clusters to generate an unprecedented threedimensional (3D) hydrogen-bonded polypseudo-rotaxane architecture. The [Cd 2 (bpa) 2 ] structural units as secondary building blocks (SBUs) are extended into metal-organic frameworks (MOFs) in 2 and 3 as 1D chains, while in 4 as 2D gridlike sheets by bridging dicarboxylate. These MOFs host meso-helical water chains, (H 2 O) 32 water clusters, and T4(1)4(2)6(2) water tapes, respectively. All of these water morphologies have not been documented so far, and the observations indicate that an SBU and various carboxylate ligands including acetate and alkyl dicarboxylate with different lengths and flexibilities can self-assemble into diverse host frameworks from tetranuclear clusters to 1D chains and ladders, finally to 2D sheets, in which guest water molecules with different morphologies can be tuned to fill the spaces of the host MOFs.

Construction of two Cd(II) complexes by flexible adipic acid plus 2-((benzoimidazol-yl)methyl)-1H-tetrazole ligand

“…Moreover, the protonated or deprotonated carboxylate groups can behave as hydrogen bond donors or acceptors, which tend to form abundant hydrogen bonds, resulting in higher dimensionalities of open structures [17,18]. In addition, Cd(II) is able to coordinate to both Nand O-donor ligands simultaneously and the final products often exhibit promising luminescent properties [19,20].…”

From simple rings to one-dimensional channels with calix[8]arenes, water clusters, and alkali metal ions

“…Thus, reaction of 4-tert-butylcalix [8] , values similar to those found for such squares in the literature. 27 Here, the square is stabilized by two hydrogen bond interactions (O16-O9; 2.715(2) Å ) with two THF molecules, each water molecule in fact being oriented in such a way that one hydrogen atom bridges to the neighboring water molecule whereas the second hydrogen atom points outward from the square. 27,28 Further water molecules (O17 and symmetry equivalents) are linked to oxygen atoms of the calixarene ligand and are shielded by H bonding to THF ligands (O12) arranged around the sandwich structure.…”

From Simple Rings to One‐Dimensional Channels with Calix[8]arenes, Water Clusters, and Alkali Metal Ions.

“…Here, however, as with all the other alkali metals, the formation of a crystalline complex was the result of using the interfacial crystallization method. Thus, reaction of 4-tert-butylcalix [8] 27 Here, the square is stabilized by two hydrogen bond interactions (O16-O9; 2.715(2) Å ) with two THF molecules, each water molecule in fact being oriented in such a way that one hydrogen atom bridges to the neighboring water molecule whereas the second hydrogen atom points outward from the square. 27,28 Further water molecules (O17 and symmetry equivalents) are linked to oxygen atoms of the calixarene ligand and are shielded by H bonding to THF ligands (O12) arranged around the sandwich structure.…”