Abstract
We report a strategy to achieve a discrete cage molecule featuring a high level of structural hierarchy through a multiple-assembly process. A cobalt (Co) supramolecular triple-stranded helicate (Co-TSH)-based discrete molecular cage (1) is successfully synthesized and fully characterized. The solid-state structure of 1 shows that it is composed of six triple-stranded helicates interconnected by four linking cobalt species. This is an unusual example of a highly symmetric cage architecture resulting from the coordination-driven assembly of metallosupramolecular modules. The molecular cage 1 shows much higher CO2 uptake properties and selectivity compared with the separate supramolecular modules (Co-TSH, complex 2) and other molecular platforms.
Highlights
Over the past decades, discrete metallosupramolecular platforms with a high degree of symmetry and intricacy have been extensively investigated owing to their promising applications in a variety of fields, including host-guest interactions[1,2], catalysis[3,4,5,6], drug delivery[7,8], gas storage, and separation[9,10,11]
The solid-state structure of 1 shows that it is composed of six cobalt supramolecular triple-stranded helicate (Co-TSH) interconnected by the four linking cobalt atoms (Co5) (Fig. 3A–C and Supplementary Fig. S1)
Each Co-TSH forms coordination bonds with two Co5 atoms through its unoccupied carboxylate oxygen atoms (Supplementary Fig. S3), and each Co5 atom with a pseudo-octahedral coordination geometry is interconnected to three neighboring Co-TSHs (Supplementary Fig. S4)
Summary
Discrete metallosupramolecular platforms with a high degree of symmetry and intricacy have been extensively investigated owing to their promising applications in a variety of fields, including host-guest interactions[1,2], catalysis[3,4,5,6], drug delivery[7,8], gas storage, and separation[9,10,11]. This assembly mode, corresponding to “tertiary” assembly, as shown, is concerned with the use of predefined, well-organized, and secondarily-assembled metallosupramolecular modules, permitting access to systematic molecular architectures In other words, such molecules can be built from three distinct levels of structural hierarchy. Clear-cut innovations of tertiary assembly over the corresponding primary and secondary assemblies can be addressed as follows: first, structurally well-organized, highly-ordered metallosupramolecular modules acting as the basic platforms can provide diverse assembly fashions. This enables the construction of hierarchical discrete platforms possessing target-oriented properties that can rarely be obtained in individual units. Cage shows a significant enhancement in selective CO2 capture over other gases under ambient conditions compared with other single molecules constructed from metal ions/clusters and organic ligands
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