Chem: 2D机械互锁COFs

Scheme.1 Schematic representation of the synthesis of the cadmium [2]catenate, the organic [2]catenane, and the catenated materials. (A) Upper: chemical structure of the cadmium [2]catenate (Cd[2]C) and the demetallated organic [2]catenane ([2]C). Lower: chemical structure of the [2]catenate- and the [2]catenane-bridged COFs; carbons are color coded with pink, red, and blue, nitrogen color coded with green, cadmium(II) with yellow, and oxygen with orange. Reaction conditions: (i) (a) Cd(OAc)2, MeOH/H2O (1:1), 80°C, 1d, 92% and (b) NH4ReO4, MeOH/H2O, RT, 5 min, 95%; (ii) NaBH4, MeOH, RT, 1d, 89%; and (iii) Cd(OAc)2, NH4ReO4, DMF/EtOH (1:1), 80°C, 3d, 72%. (B) Space-filling view of the X-ray single-crystal structure of the [2]catenate Cd[2]C. The two mechanically interlocked, identical macrocycles are shown in red and blue.

(C) Space-filling structure of the [2]catenate-bridged Cdpoly[2]C COF obtained from powder X-ray diffraction-guided simulated structure. (D) Simulated structure of the [2]catenane [2]C. The two mechanically interlocked, identical macrocycles are shown in red and blue.

(E) Space-filling structure of Poly[2]C. For all structures, hydrogen atoms, acetate, and perrhenate counter anions are omitted for the sake of clarity.

Fig.1 Schematic representations of one- and two-dimensional catenated network structures

(A) 1D main-chain poly[n]catenane; (B) 2D main-chain poly[n]catenane; (C) 1D bridged poly [2]catenane; (D) 1D side-chain poly[2]catenane; (E) 1D pendant poly[2]catenane; (F) catenane-bridged two-periodic network, prepared in this study, through metal-templated self-assembly of a pair of ligands.

Fig.2 Solid-state NMR characterization of the metalated bridged [2]catenane network structure. (A) Solid-state 13C CP/MAS NMR spectrum of the activated Cdpoly[2]C; (B) Two-dimensional solid-state 1H-13C HETCOR CP/MAS NMR spectrum of Cdpoly[2]C; (C) 113Cd CP/MAS NMR spectra of Cd(OAc)2⋅2H2O, Cd[2]C, Cdpoly[2]C, and Poly[2]C; two-dimensional 1H-113Cd HETCOR solid-state NMR spectra of (D) Cd[2]C, (E) CdPoly[2]C, (F) asymmetric unit of Cd[2]C, and (G) Cdpoly[2]C, showing the coordination sphere around the cadmium ion and nearby protons within 5 Å of the cadmium ion.

Fig.3 Microscopic characterization of the metalated and demetallated catenane-bridged network structures. SEM (A and D), TEM (B and E; inset: lattice fringes), and AFM (C and F; inset: AFM height profile) images of Cdpoly[2]C (A–C) and Poly[2]C (D–F) network structures.

Fig.4 In-depth structural characterization of the 2D-catenated COF structure. (A) Comparison of the experimental PXRD pattern (blue) (measured using small-angle X-ray scattering) and the simulated PXRD pattern for the optimized Cdpoly[2]C COF structure (red) and the calculated Bragg positions (black bars). (B and C) 3D top and side views and 2 × 2 packed simulated structure of the Cdpoly[2]C COF. (D–H) Single layer of the Cdpoly[2]C COF structure, (E) zoomed single subunit of the polycatenate COF structure and their corresponding view of above (F) and below (G) planes, and (H) further zoomed view of the simulated structure.

Fig.5 Nano-indentation studies of the networks. (A) Schematic representation of a typical AFM nano-indentation experiment. (B) Loading and unloading curves collected for CdPoly[2]C, Poly[2]C, and their corresponding monomeric subunits and analogous polymeric material using AFM nano-indentation studies. (C) Loading and unloading curves of Cdpoly[2]C and Poly[2]C and their corresponding monomeric subunit analog’s polymeric material using conventional nano-indentation. (D) Young’s modulus values calculated with error bars for Cdpoly[2]C, Poly[2]C, PolyL, Cd[2]C, and [2]C using AFM nano-indentation and conventional nano-indentation studies. (E) Hardness values with error bars of Cdpoly[2]C, Poly[2]C, PolyL, Cd[2]C, and [2]C using AFM nano-indentation and conventional nano-indentation studies. (F) Plot of penetration depth versus Young’s modulus for Cdpoly[2]C, Poly[2]C using AFM nano-indentation experiment.

∗Error bars in the all above graphs correspond to the standard deviation derived from the mean value from five measurements.

2D covalent organic framework via catenation

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