Anionic Templates Drive Conversion between a ZnII9L6 Tricapped Trigonal Prism and ZnII6L4 Pseudo-Octahedra

This work introduces the use of 8-aminoquinoline subcomponents to generate complex three-dimensional structures. Together with a tris(formylpyridine), 8-aminoquinoline condensed around ZnII templates to produce a tris(tridentate) ligand. This ligand is incorporated into either a tricapped trigonal prismatic ZnII9L6 structure or a pair of pseudo-octahedral ZnII6L4 diastereomers, with S4 and D2 symmetries. Introduction of a methyl group onto the aminoquinoline modulated the coordination sphere of ZnII, which favored the ZnII9L6 structure and disfavored the ZnII6L4 assembly. The tricapped trigonal prismatic ZnII9L6 architecture converted into a single ZnII6L4 cage diastereomer following the addition of a dianionic 4,4′-dinitrostilbene-2,2′-disulfonate guest. Four of these guests clustered tightly at the four windows of the ZnII6L4 cage, held in place through electrostatic interactions and hydrogen bonding, stabilize a single diastereomeric configuration with S4 symmetry.

High resolution electrospray ionization mass spectra (HR-ESI-MS) were recorded on a Waters Synapt G2-Si instrument.
The solvent was reduced to 0.3 mL, and Et2O (10 mL) was then added.

Investigation of whether dilution of 2 is a factor in conversion of 2 to (G)4⊂3.
We monitored the reaction at ligand concentration of 5 or 2.5 mM at r.t. or 70 °C ( Figures S40-S42). The dilution of the ligand accelerated the conversion of 2 into (G)4⊂3 because of the poor solubility of G and (G)4⊂3.

Crystallographic analysis of interactions between Zn II
6L4 host and guests. Figure S43. Distances between hydrogen atoms on the ligands of cage and oxygen atoms on the sulfonate groups of guests.
The driving force for the binding of negatively-charged guests by positively-charged hosts is primarily electrostatic attraction. The conversion from Zn II 9L6 to Zn II 6L4 was realized not only due to electrostatic interactions, but also to van der Waals interactions and hydrogen bonding between the cage and the guests.
In the crystal structure of (G)4⊂3, the distances between hydrogen atoms on the host ligands and oxygen atoms on the sulfonate groups of guests are 2.23 to 2.56 Å, less than the 2.6 Å sum of the van der Waals radii, which suggests the existence of hydrogen bonding between them. 2 Evidence for the presence of these interactions in solution is given by NMR spectroscopy, for example by the changes in chemical shift of the imine protons following guest addition ( Figures S46, S48, S54 and S56).

Hill Equation Analyses of NMR Titrations
The binding behavior of cage 1 was studied by 1

Non-Binding Guests for Cage 1
Prospective guests (2.5 μmol, 5 equiv) and cage 1 (0.5 μmol, 1.0 equiv) were combined in CD3CN (0.5 mL) in NMR tubes. The reaction mixtures were heated at 70 °C for 1 hour. After cooling to room temperature, 1 H NMR spectra were measured.
No changes in chemical shift were observed for the following species: Figure S63. Non-binding prospective guests. In this work, we introduce the use of the 8-aminoquinoline subcomponent condensing with a tritopic 2-formylpyridine to form ligands where the pyridyl moiety cannot rotate freely due to steric hindrance. The arms in the ligands of other, analogous pseudooctahedra (Table S2, entries 1-6) can rotate freely without any steric hindrance. The torsional steric hindrance of our new ligand, combined with the coordinate geometry of its vertices (Table S2, entry 7) led to the formation of M6L4 cages with D2 and S4 point symmetries rather than the higher symmetry octahedra (Table S2, entries 1-6).

X-ray Crystallography
Crystallographic data were deposited with the CCDC (2180301). Data integration and reduction were undertaken with Xia2. 5 Subsequent computations were carried out using the WinGX-32 graphical user interface. 6 A multi-scan empirical absorption correction using spherical harmonics was applied to the data using DIALS.
5b The structure was solved by intrinsic phasing using SHELXT 7 then refined and extended with SHELXL. 8 Carbon-bound hydrogen atoms were included in idealized positions and refined using a riding model. Disorder was modelled using standard crystallographic methods including constraints and restraints where necessary.
The crystals employed immediately lost solvent after removal from the mother liquor and rapid handling prior to flash cooling in liquid nitrogen was required to collect data. Despite these measures and the use of synchrotron radiation few reflections at greater than 1.15 Å resolution were observed and the data were trimmed accordingly.
Furthermore, there was a significant drop-off in diffraction intensity after around 1.5 Å resolution resulting in a low ratio of observed/unique reflections. Nevertheless, the quality of the data is far more than sufficient to establish the connectivity of the structure.
The asymmetric unit was found to contain one half of a Zn II 6L4 assembly and two 4,4'dinitrostilbene-2,2'-disulfonate guests as well as associated counterions and solvent molecules.
Due to the limited resolution, the bond lengths, and angles of the two chemically identical organic ligands were restrained to be similar to each other (SAME). Likewise, the two 4,4'-dinitrostilbene-2,2'-disulfonate guests were restrained to have similar bond lengths and angles to each other. Additional DFIX restraints were applied to some parts of the structure displaying higher degrees of thermal motion. Thermal parameter restraints (SIMU, RIGU) were applied to all atoms except for zinc to facilitate a stable anisotropic refinement.
Four additional anions per Zn II 6L4 assembly (i.e., two per asymmetric unit) are required for charge balance. These anions (included as triflimide in the formula below) were significantly disordered and despite numerous attempts at modelling, including with rigid bodies no satisfactory model for the electron-density associated with them could be found. Therefore, the SQUEEZE 9 function of PLATON 10 was employed to remove the contribution of the electron density associated with the remaining anions and further highly disordered solvent, which gave a potential solvent accessible void of 31083 Å 3 per unit cell (a total of approximately 9478 electrons). Diffuse solvent molecules could not be assigned to acetontrile or diethyl ether and were therefore not included in the formula. Consequently, the molecular weight and density given above are underestimated.
CheckCIF gives one A and two B level alerts. These alerts mostly result from the limited resolution of the data with one alert also resulting from a short contact between two ligand protons which appears to be a genuine feature of the structure, arising from the preferred conformation of the ligand.

Volume Calculations
To determine the available void space within the PM7-optimized molecular models 11 of    with C3 configuration, d) 1 with T configuration, e) 1 with S4 configuration, f) 1 with D2 configuration, g) Ligand.    framework, appears to lead to larger dihedral angles between quinolines and pyridyl rings (Table S7, entries 3-4), rendering the cage vertices more twisted. In comparing the dihedral angles between phenylene and pyridyl rings of the models (Table S7, entries 3-4), the introduction of methyl group during the construction of Zn II 9L6 also appears to increase the dihedral angles, leading to a reduction the steric hindrance between phenylene and pyridyl rings. Therefore, the presence of methyl groups introduces a twist into the vertices of cages, as the dihedral angles between quinolines and pyridyl rings become larger in Zn II 9L6 structure, and further affects the dihedral angles between phenylene and pyridyl rings, resulting in the reduction of steric hindrance. The analysis of previously-published structures (Table S7, entries 1-2) also suggests that the introduction of methyl groups would be unfavorable to the formation of M6L4 architectures.