Tunable Fullerene Affinity of Cages, Bowls and Rings Assembled by PdII Coordination Sphere Engineering

Abstract For metal‐mediated host compounds, the development of strategies to reduce symmetry and introduce multiple functionalities in a non‐statistical way is a challenging task. We show that the introduction of steric stress around the coordination environment of square‐planar PdII cations and bis‐monodentate nitrogen donor ligands allows to control the size and shape of the assembled product, from [Pd2L4] cages over [Pd2L3] bowl‐shaped structures to [Pd2L2] rings. Therefore, banana‐shaped ligand backbones were equipped with pyridines, two different quinoline isomers and acridine, the latter three introducing steric congestion through hydrogen substituents on annelated benzene rings. Differing behavior of the four resulting hosts towards the binding of C60 and C70 fullerenes was studied and related to structural differences by NMR spectroscopy, mass spectrometry and single crystal X‐ray diffraction. The three cages based on pyridine, 6‐quinoline or 3‐quinoline donors were found to either bind C60, C70 or no fullerene at all.

1 Materials and methods

Materials
All chemicals were obtained from commercial sources and used without further purification. Fullerenes C60 and C70 were purchased from ABCR with a purity of 99.95% and Sigma-Aldrich with a purity of 98%, respectively.
Syntheses and characterization of ligands L 1 and L 2 as well as their self-assembled cages and bowls, i.e. been reported previously. [1] Figure S1 Chemical structures of all ligands used in this study.
Supporting Information S3 Figure S2 Overview of previously reported self-assembly and host-guest results. [1]

Analytical techniques
Gel permeation chromatography (GPC) purification of ligands was performed on a JASCO LC-9210 II NEXT running with CHCl3 (HPLC grade) containing 0.5% (v/v) triethylamine. NMR measurements were all conducted at 298 K on Avance-500 and Avance-600 instruments from Bruker and an INOVA 500 MHz machine from Varian. Chemical shifts for 1 H and 13  with the aid of 2D NMR spectra. The proton signal at 7.58 ppm arising in some NMR spectra (298 K, CD3CN) can be assigned to traces of residual CHCl3, co-crystallized with some ligands after purification. High resolution electrospray ionization mass spectrometry (ESI HRMS) was performed on Bruker Apex IV FTICR, Bruker compact and Bruker timsTOF ESI mass spectrometers. The samples were diluted with spectrum-grade CH3CN (1:10) prior to the measurement. UV-Vis spectra were recorded on an Agilent DAD HP-8453 UV-Vis spectrophotometer using quartz cuvettes with an optical path length of 1 mm.
This was further purified via recycling gel permeation chromatography and the solvent was removed under reduced pressure to yield the desired product as a white powder (100.1 mg, 64 %).
This was further purified via recycling gel permeation chromatography and the solvent was removed under reduced pressure to yield the desired product as a pale-yellow powder (41.6 mg, 57 %). A signal at 2.15 ppm overlapping with the solvent residual peak in the aliphatic region could be assigned via 2D NMR spectroscopy.

Ring [Pd 2 L 4 2 Cl 4 ]
A to give a yellow solid (4.0 mg, 68%). The solid is soluble in DMSO and DMF, however, proton signals of the free ligand and a second species (presumably mono-coordinated ligand) were found to arise after standing for several hours.     were studied using single crystal X-ray crystallography. The crystals of all supramolecular assemblies were extremely sensitive to loss of organic solvent. Due to the very thin (5 -20 µm) plate-like crystals, the analysis was hampered by the limited scattering power of the samples not allowing to reach the desired (sub-)atomic resolution using a modern microfocussed in-house X-ray CuKa source. Gaining detailed structural insight thus required cryogenic crystal handling and highly brilliant synchrotron radiation. Hence, diffraction data of all supramolecular assemblies was collected during three beamtime shifts at macromolecular synchrotron beamline P11, PETRA III, DESY. [3] Modelling of C70 disorder as well as counterion and solvent flexibility required carefully adapted macromolecular refinement protocols employing geometrical restraint dictionaries, similarity restraints and restraints for anisotropic displacement parameters (ADPs). immediately flash cooled in liquid nitrogen. Crystals were stored at cryogenic temperature in dry shippers, in which they were safely transported to macromolecular beamline P11 at Petra III [3] , DESY, Germany.
A wavelength of λ = 0.6888 Å was chosen using a liquid N2 cooled double crystal monochromator. Single crystal X-ray diffraction data was collected at 80(2) K on a single axis goniometer, equipped with an Oxford Cryostream 800 and a Pilatus 6M detector. 1800 diffraction images were collected in a 360° φ sweep at a detector distance of 156 mm, 30% filter transmission, 0.2° step width and 0.2 seconds exposure time per image. Data integration and reduction were undertaken using XDS. [4] The structure was solved by intrinsic phasing/direct methods using SHELXT [5] and refined with SHELXL [6] using 22 cpu cores for full-matrix least-squares routines on F 2 and ShelXle [7] as a graphical user interface and the DSR program plugin was employed for modeling. [8]

Specific refinement details of [C70@Pd2L 2 4](BF4)4
A C2 symmetry element is located at the center of the complex. Stereochemical restraints for the EAQ ligands (L 2 ) and ethyl acetate (OAC) were generated by the GRADE program using the GRADE Web Server (http://grade.globalphasing.org) and applied in the refinement. A GRADE dictionary for SHELXL contains target values and standard deviations for 1,2-distances (DFIX) and 1,3-distances (DANG), as well as restraints for planar groups (FLAT).
All displacements for non-hydrogen atoms were refined anisotropically. The refinement of ADP's for carbon, nitrogen and oxygen atoms was enabled by a combination of similarity restraints (SIMU) and rigid bond restraints (RIGU). [9] Disorder of C70 guest was modelled with two discrete positions each using the DSR program GUI and its SADI restraints for 1,2-distances, 1,3-distances and planar groups for C70. [8,10] The contribution of the electron density from disordered counterions and solvent molecules, which could not be modeled with discrete atomic positions, were handled using the SQUEEZE [11] routine in PLATON. [12] The solvent mask file (.fab) computed by PLATON were included in the SHELXL refinement via the ABIN instruction leaving the measured intensities untouched.

Crystal structure of [Pd 2 L 3 4 ](BF 4 ) 4
Colorless plate-shaped crystals of [Pd2L 3 4](BF4)4 were obtained by slow vapor diffusion of methyl tert-butyl ether into a 0.64 mM CD3CN solution of [Pd2L 3 4](BF4)4. A single crystal in mother liquor was pipetted onto a glass slide containing NVH oil. To avoid collapse of the crystal lattice, the crystal was quickly mounted onto a 0.1 mm nylon loop and immediately flash cooled in liquid nitrogen. Crystals were stored at cryogenic temperature in dry shippers, in which they were safely transported to macromolecular beamline P11 at Petra III [3] , DESY, Germany.
A wavelength of λ = 0.6888 Å was chosen using a liquid N2 cooled double crystal monochromator. Single crystal X-ray diffraction data was collected at 80(2) K on a single axis goniometer, equipped with an Oxford Cryostream 800 and a Pilatus 6M detector. 1800 diffraction images were collected in a 360° φ sweep at a detector distance of 156 mm, 30% filter transmission, 0.2° step width and 0.2 seconds exposure time per image. Data integration and reduction were undertaken using XDS. [4] The structure was solved by intrinsic phasing/direct methods using SHELXT [5] and refined with SHELXL [6] using 22 cpu cores for full-matrix least-squares routines on F 2 and ShelXle [7] as a graphical user interface and the DSR program plugin was employed for modeling. [8]

Specific refinement details of [Pd2L 3 4](BF4)4
The occupancies of two Pd atoms and three BF4 moieties were refined with 0.25 owing to the C4 symmetry element oriented along the Pd-Pd axis. Stereochemical restraints for the ETQ ligands (L 3 ) were generated by the GRADE program using the GRADE Web Server (http://grade.globalphasing.org) and applied in the refinement. A GRADE dictionary for SHELXL contains target values and standard deviations for 1,2-distances (DFIX) and 1,3-distances (DANG), as well as restraints for planar groups (FLAT). All displacements for non-hydrogen atoms were refined anisotropically. The refinement of ADP's for carbon, nitrogen and oxygen atoms was enabled by a combination of similarity restraints (SIMU) and rigid bond restraints (RIGU). [9] The contribution of the electron density from disordered counterions and solvent molecules, which could not be modeled with discrete atomic positions, were handled using the SQUEEZE [11] routine in PLATON. [12] The solvent mask file (.fab) computed by PLATON were included in the SHELXL refinement via the ABIN instruction leaving the measured intensities untouched.

Crystal structure of [Pd 2 L 4 2 Cl 4 ]
Colorless plate-shaped crystals of [Pd2L 4 2Cl4] were obtained by slow vapor diffusion of benzene into a 0.64 mM CD3CN solution (100 μL) of [Pd2L 4 2(MeCN)4](BF4)4 in the presence of 5 eq. of tetrabutylammonium periodate (TBAIO4). A single crystal in mother liquor was pipetted onto a glass slide containing NVH oil. To avoid collapse of the crystal lattice, the crystal was quickly mounted onto a 0.1 mm nylon loop and immediately flash cooled in liquid nitrogen. Crystals were stored at cryogenic temperature in dry shippers, in which they were safely transported to macromolecular beamline P11 at Petra III [3] , DESY, Germany.
A wavelength of λ = 0.6888 Å was chosen using a liquid N2 cooled double crystal monochromator. Single crystal X-ray diffraction data was collected at 80(2) K on a single axis goniometer, equipped with an Oxford Cryostream 800 and a Pilatus 6M detector. 1800 diffraction images were collected in a 360° φ sweep at a detector distance of 156 mm, 30% filter transmission, 0.2° step width and 0.2 seconds exposure time per image. Data integration and reduction were undertaken using XDS. [4] The structure was solved by intrinsic phasing/direct methods using SHELXT [5] and refined with SHELXL [6] using 22 cpu cores for full-matrix least-squares routines on F 2 and ShelXle [7] as a graphical user interface and the DSR program plugin was employed for modeling. [8]

Specific refinement details of [Pd2L 4 2Cl4]
The chloride atoms were assigned crystallographically by the electron density and the bond distances (Pd-Cl: 2.33 Å), although chloride anions were not meant to be contained in the solution of sample [Pd2L 4 2(MeCN)4](BF4)4. We presume that the observed chloride ions came from a contamination in the added TBAIO4 or the partial decomposition of CHCl3 which was used in the last purification step for ligand L 4 . Stereochemical restraints for the EAA ligands (L 4 ) were generated by the GRADE program using the GRADE Web Server (http://grade.globalphasing.org) and applied in the refinement. A GRADE dictionary for SHELXL contains target values and standard deviations for 1,2-distances (DFIX) and 1,3-distances (DANG), as well as restraints for planar groups (FLAT). All displacements for non-hydrogen atoms were refined anisotropically. The refinement of ADP's for carbon, nitrogen and oxygen atoms was enabled by a combination of similarity restraints (SIMU) and rigid bond restraints (RIGU). [9] The contribution of the electron density from disordered counterions and solvent molecules, which could not be modeled with discrete atomic positions, were handled using the SQUEEZE [11] routine in PLATON. [12] The solvent mask file (.fab) computed by PLATON were included in the SHELXL refinement via the ABIN instruction leaving the measured intensities untouched.   4 in the presence of 10 eq. of tetrabutylammonium periodate (TBAIO4). A single crystal in mother liquor was pipetted onto a glass slide containing NVH oil. To avoid collapse of the crystal lattice, the crystal was quickly mounted onto a 0.1 mm nylon loop and immediately flash cooled in liquid nitrogen. Crystals were stored at cryogenic temperature in dry shippers, in which they were safely transported to macromolecular beamline P11 at Petra III [3] , DESY, Germany.
A wavelength of λ = 0.6888 Å was chosen using a liquid N2 cooled double crystal monochromator. Single crystal X-ray diffraction data was collected at 80(2) K on a single axis goniometer, equipped with an Oxford Cryostream 800 and a Pilatus 6M detector. 1900 diffraction images were collected in a 360° φ sweep at a detector distance of 200 mm, 100% filter transmission, 0.2° step width and 0.1 seconds exposure time per image. Data integration and reduction were undertaken using XDS. [4] The structure was solved by intrinsic phasing/direct methods using SHELXT [5] and refined with SHELXL [6] using 22 cpu cores for full-matrix least-squares routines on F 2 and ShelXle [7] as a graphical user interface and the DSR program plugin was employed for modeling. [8]

Specific refinement details of [Pd2L 4 2Cl4]_B
The chloride atoms were assigned crystallographically by the electron density and the bond distances (Pd-Cl: 2.33 Å), although chloride anions were not meant to be contained in the solution of sample [Pd2L 4 2(MeCN)4](BF4)4. We presume that the observed chloride ions came from a contamination in the added TBAIO4 or the partial decomposition of CHCl3 which was used in the last purification step for ligand L 4 . Stereochemical restraints for the EAA ligands (L 4 ) were generated by the GRADE program using the GRADE Web Server (http://grade.globalphasing.org) and applied in the refinement. A GRADE dictionary for SHELXL contains target values and standard deviations for 1,2-distances (DFIX) and 1,3-distances (DANG), as well as restraints for planar groups (FLAT). All displacements for non-hydrogen atoms were refined anisotropically. The refinement of ADP's for carbon, nitrogen and oxygen atoms was enabled by a combination of similarity restraints (SIMU) and rigid bond restraints (RIGU). [9] The contribution of the electron density from disordered counterions and solvent molecules, which could not be modeled with discrete atomic positions, were handled using the SQUEEZE [11] routine in PLATON. [12] The solvent mask file (.fab) computed by PLATON were included in the SHELXL refinement via the ABIN instruction leaving the measured intensities untouched.   [13] using a primary grid and plot grid spacing of 0.1 Å and 10 cycles of volume refinement with the size probe radius of 3.2 Å, the minimum radius such that it would not exit the cavity of this series of structures. Molecular visualization was done using PyMol. [14]

Computational studies
All models shown below were constructed using Wavefunction SPARTAN '14 [15] and first optimized on semiempiric PM6 level of theory without constraints. The resulting structures were then further refined by DFT structure optimization (B3LYP/C, H, N, O = 6-31g(d)/Pd LANL2DZ) using GAUSSIAN 09. [16]