Backbone‐Bridging Promotes Diversity in Heteroleptic Cages

Abstract

The combination of shape-complementary bismonodentate ligands L A and L B with Pd(II) cations yields heteroleptic cages cis-[Pd2L A 2L B 2] by non-statistical self-assembly. Here we report how such assemblies can be diversified by introduction of covalent backbone bridges between two L A units. Together with solvent-and guest-effects, the flexibility of these linkers is shown to modulate the nuclearity, topology and number of distinguishable cavities in a family of four structurally highly diverse supramolecular assemblies. Liganddimer L A1 , with flexibly connected backbones, reacts in acetonitrile with its L B counterpart to a tetranuclear back-to-back dimer of heteroleptic cages D1. In DMSO, however, a trinuclear pseudotetrahedral structure T1 is formed. The product of L A2 , with rigidly connected backbones, looks similar to D1, but with a rotated ligand arrangement. In presence of an anionic guest, this dimer D2 transforms and a hexanuclear prismatic barrel P2 crystallizes. We demonstrate how controlling a ligand's coordination mode can trigger structural differentiation and increase complexity in metallosupramolecular assembly.

Increasing structural and functional complexity in self-assembled coordination cages

“…18 ). 97 Based on the observation that ligand 43 cleanly forms cis -[Pd 2 43 2 26 2 ] heteroleptic cages with above-introduced carbazole-derived ligand 26 , a series of higher-order assemblies was achieved. When 43 was mixed with dual ligand 44 , in which both carbazole sites are back-to-back connected with a flexible linker, Pd II coordination in acetonitrile afforded [Pd 4 43 4 44 2 ] as a formal dimer of cis -[Pd 2 43 2 26 2 ].…”

Tuning the Size and Geometry of Heteroleptic Coordination Cages by Varying the Ligand Bent Angle

“…For the construction of Pd II -based metal-ligand assemblies, polydentate N-donor ligands were found to be well suited. [12][13][14][15][16][17] Elaborate polypyridyl ligands were used to build complex molecular architectures, [18][19][20][21][22][23][24][25] but even simple di-4-pyridyl ligands can give rise to assemblies with up to 48 Pd II ions. [26] A crucial design element for di-4-pyridyl ligands is the bent angle α between the two coordinate vectors of the pyridyl groups (Scheme 1).…”

Integrative Assembly of Heteroleptic Tetrahedra Controlled by Backbone Steric Bulk

“…To overcome the formation of a statistical mixture, 44 several strategies have been applied, e.g., exploiting hydrogen-bonding, 45 templating guests, 46 shape complementarity, 47 − 53 or covalent bridges between ligands. 54 Herein, we report a system where a bis-monodentate, flat ligand L A self-assembles with Pd II to give a series of [Pd n L 2 n ] ( n = 3, 4, 6) architectures in a solvent-dependent process. Introduction of steric congestion into its backbone gives the bulky ligand L B , allowing us to exclusively form a large [Pd 6 L 12 ] octahedron.…”