Homochiral Emissive Λ8‐ and Δ8‐[Ir8Pd4]16+ Supramolecular Cages

Abstract Synthetic self‐assembly is a powerful technique for the bottom‐up construction of discrete and well‐defined polyhedral nanostructures resembling the spherical shape of large biological systems. In recent years, numerous Archimedean‐shaped coordination cages have been reported based on the assembly of bent monodentate organic ligands containing two or more distal pyridyl rings and square‐planar PdII ions. The formation of photoactive PdII metallamacrocycles and cages, however, remain rare. Here we report the first examples of emissive and homochiral supramolecular cages of the form [Ir8Pd4]16+. These cages provide a suitably sized cavity to host large guest molecules. Importantly, encapsulation and energy transfer have been observed between the blue‐emitting NBu4[Ir(dFppy)2(CN)2] guest and the red‐emitting Δ8‐[Ir8Pd4]16+ cage.


Experimental section.
General Synthetic Procedures. Commercial chemicals were used as supplied. All reactions in the synthesis of the metalloligands and metallocages were performed using standard Schlenk techniques under inert (N 2 ) atmosphere with reagent-grade solvents. Flash column chromatography was performed using silica gel (Silia-P from Silicycle, 60 Å, 40-63 µm). Analytical thin layer chromatography (TLC) was performed with silica plates with aluminum backings (250 µm with indicator F-254). Compounds were visualized under UV light. 1 H (including 1 H DOSY), 13 C and 19 F solution-phase NMR spectra were recorded on a Bruker Avance spectrometer operating at 11.7 T (Larmor frequencies of 500, 126 and 471 MHz, respectively). The following abbreviations have been used for multiplicity assignments: "s" for singlet, "d" for doublet, "t" for triplet, "m" for
Host-Guest chemistry with small organic compounds. Figure S48. 1

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Crystal Structures of Λ,Λ-and Δ,Δ-D2 and rac-2 X-ray diffraction data for compounds Λ,Λ-and Δ,Δ-D2 and rac-2 were collected at 93 K by using a Rigaku FR-X Ultrahigh brilliance Microfocus RA generator/confocal optics and Rigaku XtaLAB P200 system, with Mo Kα radiation (λ = 0.71075 Å). Intensity data were collected using ω steps accumulating area detector images spanning at least a hemisphere of reciprocal space. All data were corrected for Lorentz polarization effects. A multiscan absorption correction was applied by using either CrystalClear (Λ,Λ-D2 and rac-2) 7 or CrysalisPro (Δ,Δ-D2). 8 Structures were solved by Patterson methods (PATTY) 9 and refined by full-matrix least-squares against F 2 (SHELXL-2014). 10 Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using a riding model. All calculations were performed using the CrystalStructure 11 interface. Crystallographic data are presented in Table S2. Thermal ellipsoid plots of the structures are Repeated attempts were made at collecting X-ray diffraction data on cages C1 and C2. The best data obtained to date, for rac-C1, was collected at beamline I19, Diamond Light Source, Didcot, UK using silicon double crystal monochromated radiation (λ = 0.6889 Å, Pilatus 2M detector), 12 at 100 K. A multiscan absorption correction was applied by using CrysalisPro. 8 A solution was obtained using charge-flipping methods (Superflip), 13 which revealed the positions of the metal centers and an approximation of the structure of the ligand ( Figure S62), however it has not, as yet, been possible to refine the data. Calculations were performed using the WinGX interface. 14     Emission spectra (DCM solution and PMMA-doped films).

Determination of binding constant for the formation of Δ-C1⊃IrCN
The binding constant for the host-guest structure Δ-C1⊃IrCN was determined from emission titration experiments (see Figure 7). Small aliquots of Δ-C1 were added to a 100 μM degassed solution of IrCN in DMSO such that the concentration of Δ-C1 in the sample ranged from 0 μM to 120 μM. An emission spectrum of the solution was recorded after each addition and the variation of the emission intensity of IrCN in Δ-C1⊃IrCN with respect to Δ-C1 concentration determined from this data. This data was then fitted to the sequential 1:1 binding model 18 using an iterative fitting S-65 procedure implemented within the OpenDataFit tool of the Supramolecular program (www.supramolecular.org) (see Figure S79). The best fit of the binding model to the emission data afforded a value for K b of 3.9 × 10 6 ± 0.2 M -1 .

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Energy Transfer Studies between Irdmbpy and Δ-C1. In contrast to that observed for the Δ-C1⊃IrCN assemblies, no energy transfer was observed between Irdmbpy and Δ-C1. Indeed, the emission intensity of Irdmbpy (λ em = 480 nm) increases proportionally with concentration. The emission intensity of Δ-C1 is also not affected by the addition of Irdmbpy. The same conclusion can be extracted from the time-resolved emission experiments presented below.
S-71 Emission decays monitored at 520 nm of Irdmbpy and Irdmbpy after gradual addition of Δ-C1 (quencher) in degassed DMSO at 298 K.

Computational details
All calculations are based on Hartree Fock theory (HF) theory. The geometries of the host and hostguest complexes were fully optimized without symmetry restriction in the gas phase using the 6-31G(d) basis set for the light atoms. Scalar relativistic effects were included for the Ir and Pd atoms by using the LANL2DZ pseudopotentials. 19 All calculations were carried out with the Gaussian09.D01 program package. 20