A New Mechanically‐Interlocked [Pd₂L₄] Cage Motif by Dimerization of two Peptide‐based Lemniscates

Abstract

Most metallo-supramolecular assemblies of low nuclearity adopt simple topologies, with bridging ligands spanning neighboring metal centers in a direct fashion. Here we contribute a new structural motif to the family of host compounds with low metal count (two) that consists of a pair of doubly-interlocked, Figure-eight-shaped subunits, also termed "lemniscates". Each metal is chelated by two chiral bidentate ligands, composed of a peptidic macrocycle that resembles a natural product with two pyridyl-terminated arms. DFT calculation results suggest that dimerization of the mononuclear halves is driven by a combination of 1) Coulomb interaction with a central anion, 2) p-stacking between intertwined ligand arms and 3) dispersive interactions between the structures compact inner core bedded into an outer shell composed of the cavitand-type macrocycles. The resulting cage-like architecture was characterized by NMR, MS and Xray structure analyses. This new mechanically bonded system highlights the scope of structural variety accessible in metalmediated self-assemblies composed of only a few constituents.

Increasing structural and functional complexity in self-assembled coordination cages

“… 60 Recently, we contributed a [Pd 2 L 4 ] host with a new mechanically-interlocked motif, consisting of a pair of doubly-interlocked, figure-eight-shaped lemniscates. 30 Even higher complexity was reported by Lützen and co-workers, with a rotaxane-like cage-in-ring structural motif, where a BODIPY-based bis-pyridine ligand ( 1 ) self-assembles with Pd II cations to form a compound of [Pd 6 1 12 ] stoichiometry ( Fig. 3a ).…”

“… 29 Organic bridges are multitopic ligands with two or more donors of same or differing chemical structure and a backbone that determines size and shape of the assembly and can carry extra functional or solubilizing groups. While the individual donor groups can be mono- or multidentate, ligands are usually designed not to chelate the same metal so they serve as bridges between different metal nodes (a recent notable exception is a cavity formed by a pair of mechanically entangled “figure-eight”-shaped Pd II -chelate complexes 30 ).…”

Ion Mobility Mass Spectrometry Uncovers Guest‐Induced Distortions in a Supramolecular Organometallic Metallosquare

“…Examples of the use of the IM‐MS technique have been reported for supramolecular coordination complexes (SCCs) supported by N‐, O‐ donor, Werner‐type ligands, and include topological characterization studies [7] and the identification of geometric isomers [8] . Furthermore, recent studies showed that IM‐MS could be used to visualize the expansion and contraction of chiral palladium cages upon addition of different guests [7l,m] …”

Coordination/Metal–Organic Cages Inside Out

“…Note that the synthetic parameters for this analysis do not include those related to the reactions that prepare the starting materials. For example, some procedures for the formation of CCs involve anion exchange reactions of metal salts before adding the ligand [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]. This process is excluded from the meta-analysis to compare only the quantitative comparison of the reaction time and temperature, "immediate" and "overnight" were interpreted as 1 min and 12 h, respectively.…”