Supramolecular Mille-Feuille: Adaptive Guest Inclusion in a New Aliphatic Guanidinium Monosulfonate Hydrogen-Bonded Framework

Abstract

During the past three decades, the ability of guanidinium arenesulfonate host frameworks to encapsulate a wide range of guests has been amply demonstrated, with more than 700 inclusion compounds realized. Herein, we report crystalline inclusion compounds based on a new aliphatic host, guanidinium cyclohexanemonosulfonate, which surprisingly exhibits four heretofore unobserved architectures, as described by the projection topologies of the organosulfonate residues above and below hydrogen-bonded guanidinium sulfonate sheets. The inclusion compounds adopt a layer motif of guanidinium sulfonate sheets interleaved with guest molecules, resembling a mille-feuille pastry. The aliphatic character of this remarkably simple host, combined with access to greater architectural diversity and adaptability, enables the host framework to accommodate a wide range of guests and promises to expand the utility of guanidinium organosulfonate hosts.

Figure 1

Quasi-hexagonal hydrogen-bonded sheet formed by guanidinium and organosulfonate ions. The sheet can be described as 1D GS “ribbons” fused along the ribbon edges by lateral (G)N⁺–H···^–O(S) hydrogen bonds, which serve as flexible “hinges” that permit puckering of the sheet over a wide range of angles, denoted as the inter-ribbon puckering angle (θ_IR) (Figure S1). The molecular structure of guanidinium cyclohexanemonosulfonate (GCHMS) is depicted at the bottom right.

Figure 2

Schematic representations of the previously observed inclusion compound architectures for GS frameworks formed from guanidinium organomonosulfonate hosts. s-CLIC = simple continuous layered inclusion compound; d-CLIC = double continuous layered inclusion compound; zz-CLIC = zigzag continuous layered inclusion compound; and TIC = tubular inclusion compound. A single organomonosulfonate host can form each of these architectures as a consequence of guest templating, illustrating architectural isomerism. The zz-CLIC depiction here signifies two unique architectures formed by distinct projection topologies (zz-CLIC I and zz-CLIC II, Figure S2).

Figure 3

Molecular structures of the 19 guests included in the GCHMS host. Guest volumes (V_g) and the corresponding framework architectures of the inclusion compounds are denoted below each guest structure. Compound 5 contains both stereoisomers of cis-rose oxide in equal amounts; the stereochemistry is not denoted here for the sake of clarity.

Figure 4

Projection topologies of the GS sheets observed in GCHMS inclusion compounds. The top four topologies have not been observed previously. Filled and open circles depict organic groups projecting from the sulfonate nodes above and below the sheet, respectively. The guanidinium ions sit on the undecorated nodes of the hexagonal tiling. The blue parallelograms depict the translational repeat unit of each sheet. The red parallelograms represent the “tetrad” repeat units that contain guest molecules in the Tetrad I–III architectures (Figure S4). The formalism that describes the unique projection sequence of that architecture can be found in Table S3.

Figure 5

Crystal structures of (A, B) (GCHMS)₃⊃2-bromocyclooctanone (1) in the Tetrad I architecture, (C, D) (GCHMS)₄⊃nicotine (2) in the Tetrad II architecture and (E, F) (GCHMS)₄⊃cis-rose oxide (5) in the Tetrad III architecture. The left panels depict the frameworks as ball-and-stick and the guest molecules as space-filling. Panels on the right illustrate top-down views of one side of each GS sheet with organic residues rendered as space-filling. Guest molecules are denoted as green ovals for the sake of clarity. Red parallelograms denote the repeat tetrad locations illustrated in Figure 4.

Figure 6

Crystal structure of (GCHMS)₃⊃2-chlorocyclooctanone (8) in the DLIC architecture and (GCHMS)₂⊃sclareolide (10) in an “expanded”-DLIC architecture. The frameworks are depicted as ball-and-stick and the guest molecules as space-filling.

Figure 7

Crystal structures of (A) GCHMS⊃1,4-dioxane (11) in the s-CLIC architecture and (B) (GCHMS)₂⊃γ-terpinene (14) in the zz-CLIC I architecture. The frameworks are depicted as ball-and-stick and the guest molecules as space-filling.

Figure 8

Crystal structures of (A) (GCHMS)₃⊃ROY (17) and (B) (GCHMS)₃⊃eucalyptol (18) in an s-CLIC architecture, where adjacent sheets are further apart than typically observed. The frameworks are depicted as ball-and-stick and the guest molecules as space-filling.