Nature has been a source of scientific inspiration because the relations between structure and function are associated with their behaviors in molecular level. Inspired by the nature’s elaborated fashion, we report several synthetic receptors involving crown ethers, calixarenes, pillararenes, and acyclic chelates which recognize specific organic guests via the metal-driven adaptation.^1-6
The regioisomers of bis-dithiamacrocycle o-bis-L (W-shape binding site) and m-bis-L (U-shape binding site) react with CuI to yield 1-D polymers, in which each isomer is linked by cubane [Cu₄I₄] cluster and square [Cu₂I₂] cluster, respectively (Fig. 1).² The results illustrate the possibility for the adaptive formations of the clusters through the binding site design or alternation.
Post-synthetic modifications (PSMs) via an SCSC transformation provide a powerful tool, not only for creating of new materials, but also for understanding mechanistic pathways. We report an anion exchange process accompanying cation reduction and dimerization via the SCSC transformation.³
Calix[6]-crown-5 allowed us to isolate molecular capsules incorporating both homo- and heteromultinuclear alkali metal ions in a head-to-head fashion in which the bowl-type host units act as a glue to stabilize the elegant capsule arrangement (Fig. 2).⁶ To the best of our knowledge, these are the first capsule-like species which involve several homo- or hetero-metal ions.
The combination of the dicopper platform (1) and 1,4-bis(4-pyridyl)piperazine (bpp) afforded the first example of a 1-D polyrotaxane whose string and bead are constructed from the same components (Fig. 3).⁴ The formation of the polyrotaxane is driven by π-π stacking between the string and the beads with electronic and steric complementarity evident between these components.
Among the photochemical methods, [2+2] cycloaddition has been employed to generate cyclobutane based coordination polymers from the metal complexes. Our advancements in the construction of polymeric chains of cyclobutane rings via photo-dimerisation reaction containing metal complexes, coordination polymers and MOF are also introduced (Fig. 4).⁵
In biological molecular recognition, induced fit via adaptive structural changes of the receptor is more acceptable than lock-&-key principle. We report a metal-driven cascade complex with a flexible macrocycle whose organic guest recognition is anion dependent (Fig. 5).⁶ In solution, its dimercury(II) perchlorato complex recognizes dabco, but its iodo complex shows no reactivity. Crystal structures reveal that the dabco recognition is associated with a swing door manner of each coordinated anion.
Pillar[5]-bis-dithiacrown (L) shows non-selective complexations with a series of α,ω-dicyanoalkanes [CN(CH₂)_nCN, n = 2-6, shortly C2-C6] (Fig. 6).6 Upon disilver(I) complexation, L shows an adaptation to form a cascade complex with C2 in which two Ag(I) ions bound to the thiacrown rings with ~10 Å separation are linked by one C2, exhibiting a shape-changing of the host.

References
1. Park, S.; Lee, S. Y.; Park, K.-M.; Lee, S. S. Acc. Chem. Res. 2012, 45, 391.
2. Kim, S.; Siewe, A. D.; Lee, E.; Ju, H.; Park, I.-H.; Park, K.-M.; Ikeda, M.; Habata, Y.; Lee, S. S. Inorg. Chem. 2016, 55, 2018.
3. Lee, H.-H.; Park, I.-H.; Kim, S.; Lee, E.; Ju, H.; Jung, J. H.; Ikeda, M.; Habata, Y.; Lee, S. S. Chem. Sci. 2017, 8, 2592.
4. Ju, H.; Clegg, J. K.; Park, K.-M.; Lindoy, L. F.; Lee, S. S. J. Am. Chem. Soc. 2015, 137, 9535.
5. Park, I.-H.; Chanthapally, A.; Zhang, Z.; Lee, S. S.; Zaworotko, M. J.; Vittal, J. J. Angew. Chem. Int. Ed. 2014, 53, 414.
6. Unpublished data.