It is difficult to assemble multi-component metallo-supramolecular architectures in a non-statistical fashion, which limits their development toward functional materials. Herein, we report a system of interconverting bowls and cages that are able to respond to various selective stimuli (light, ligands, anions), based on the self-assembly of a photochromic dithienylethene (DTE) ligand, L a , with Pd II cations. By combining the concept of “coordination sphere engineering”, relying on bulky quinoline donors, with reversible photoswitching between the ligand’s open ( o - L a ) and closed ( c - L a ) forms, a [Pd 2 ( o - L a ) 4 ] cage ( o - C ) and a [Pd 2 ( c - L a ) 3 ] bowl ( c - B ) were obtained, respectively. This structural rearrangement modulates the system’s guest uptake capabilities. Among three bis-sulfonate guests ( G1 , G2 , and G3 ), the cage can encapsulate only the smallest ( G1 ), while the bowl binds all of them. Bowl c - B was further used to synthesize a series of heteroleptic cages, [Pd 2 L A 3 L B ], representing a motif never reported before. Additional ligands ( L c-f ), with short or long arms, tune the cavity size, thus enabling or preventing guest uptake. Addition of Br – /Ag + makes it possible to change the overall charge, again triggering guest uptake and release, as well as fourth ligand de-/recomplexation. In combination, site-selective introduction of functionality and application of external stimuli lead to an intricate system of hosts with different guest preferences. A high degree of complexity is achieved through cooperativity between only a few components.

The design of structurally defined heteroleptic coordination cages is a challenging task, and only few examples are known to date. Here we describe a selection approach that allowed the identification of a novel hexanuclear Pd cage containing two types of dipyridyl ligands. A virtual combinatorial library of [Pd n L 2n ](BF 4 ) 2n complexes was prepared by mixing six different dipyridyl ligands with substoichiometric amounts of [Pd(CH 3 CN) 4 ](BF 4 ) 2 . Analysis of the equilibrated reaction mixture revealed the preferential formation of a heteroleptic [Pd 6 L 6 L′ 6 ](BF 4 ) 12 assembly. The complex was prepared on a preparative scale by a targeted synthesis, and its structure was elucidated by single-crystal X-ray diffraction. It features an unprecedented trigonal-antiprismatic cage structure with two triangular Pd 3 L 3 macrocycles bridged by six L′ ligands. A related but significantly larger [Pd 6 L 6 L′ 6 ](BF 4 ) 12 cage was obtained by using metalloligands instead of organic dipyridyl ligands.

Spherical assemblies of the type [Pd n L 2n ] 2n + can be obtained from Pd II salts and curved N-donor ligands, L. It is well established that the bent angle, α, of the ligand is a decisive factor in the self-assembly process, with larger angles leading to complexes with a higher nuclearity, n. Herein, we report heteroleptic coordination cages of the type [Pd n L n L' n ] 2n + , for which a similar correlation between the ligand bent angle and the nuclearity is observed. Tetranuclear cages were obtained by combining [Pd(CH 3 CN) 4 ](BF 4 ) 2 with 1,3-di(pyridin-3-yl)benzene and ligands featuring a bent angle of α = 120°. The use of a dipyridyl ligand with α = 149°led to the formation of a hexanuclear complex with a trigonal prismatic geometry; for linear ligands, octanuclear assemblies of the type [Pd 8 L 8 L' 8 ] 16 + were obtained. The predictable formation of heteroleptic Pd II cages from 1,3-di(pyridin-3-yl) benzene and different dipyridyl ligands is evidence that there are entire classes of heteroleptic cage structures that are privileged from a thermodynamic point of view.

A new series of [Pd2(L)4] cages based on photochromic dithienylethene (DTE) ligands allowed us to gain insight into the successive photoswitching of multiple DTE moieties in a confined metallo‐supramolecular assembly. Three new X‐ray structures of [Pd2(o‐L4)4], [Pd2(o‐L1)2(c‐L1)2] and [Pd2(c‐L1)4] (o‐L and c‐L = open and closed forms of DTE ligands, respectively) were obtained. The structures deliver snapshots of three different combinations of DTE photoisomeric states within the cage, facilitating a comparison of the all‐open with the all‐closed, and most notably, an intermediate form where open and closed switches co‐exist in the same cage. Moreover, a series of spherical anionic borate clusters was introduced in order to study their roles in the light‐controllable host–guest chemistry. The binding guests show higher affinities with the flexible open cage [Pd2(o‐L1)4] than with the rigid closed cage [Pd2(c‐L1)4]. For the [B12F12]2− guest, thermodynamic data obtained from NMR experiments was compared to results from isothermal titration calorimetry (ITC).

Structurally defined Pd4L8 and Pd6L12 coordination cages are obtained from low-symmetry dipyridyl ligands.