By choosing an appropriate ligand, it is possible to influence the size, the geometry and the functionality of a metallasupramolecular assembly. Functionalized clathrochelate complexes have recently emerged as a promising new class of metalloligands for applications in supramolecular coordination chemistry. [1] The reaction of cis-blocked, square planar M^II complexes with tetratopic N-donor ligands is known to give metallasupramolecular assemblies of the formula M_2nL_n. We recently demonstrate that unusual geometries are accessible like the Pt₈L₄ cage with gyrobifastigium-like geometry. [2] A geometric analysis of the ligands could explain how size and geometry influence the self-assembly process. The metalloligands used gave assemblies of type Pt₈L₄, which adopt barrel- or gyrobifastigium-like structures (Figure 1A and 1B). Larger assemblies are possible, as Pt₁₀L₅ complex and a Pt₁₆L₈ complex (Figure 1C and 1D). The latter has a molecular weight of more than 23 kDa and a diameter of 4.5 nm, making it the largest, structurally characterized M_2nL_n complex described to date.

By X-ray crystallography, we characterize both new of M_2nL_n complexes, namely a pentagonal Pt₁₀L₅ barrel and a Pt₁₆L₈ complex (Figure 2A and 2B). The latter assembly displays an unprecedented square orthobicupola geometry. Overall, we think that our study will provide an important foundation for future investigations of coordination barrels.

[1] G. Cecot, S. M. Jansze, M. D. Wise, K. O. Zhurov, T. K. Ronson, A. M. Castilla, A. Finelli, P. Pattison, E. Solari, R. Scopelliti, G. E. Zelinskii, A. V. Vologzhanina, Y. Z. Voloshin, J. R. Nitschke, K. Severin, J. Am. Chem. Soc. 2016, 138, 2046-2054.
[2] G. Cecot, B. Alameddine, S. Prior, R. De Zorzi, S. Geremia, R. Scopelliti, F. T. Fadaei, E. Solari, K. Severin, Chem. Commun. 2016, 48, 11243-11246.