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. 2024 May 22;146(20):14128-14135.
doi: 10.1021/jacs.4c02673. Epub 2024 May 9.

2D to 3D Reconstruction of Boron-Linked Covalent-Organic Frameworks

Xue Wang  1   2 , Thomas Fellowes  1   2 , Mounib Bahri  3 , Hang Qu  2 , Boyu Li  2 , Hongjun Niu  2 , Nigel D Browning  3 , Weiwei Zhang  4 , John W Ward  1   2 , Andrew I Cooper  1   2
Affiliations

2D to 3D Reconstruction of Boron-Linked Covalent-Organic Frameworks

Xue Wang et al. J Am Chem Soc. .

Abstract

The transformation of two-dimensional (2D) covalent-organic frameworks (COFs) into three-dimensions (3D) is synthetically challenging, and it is typically addressed through interlayer cross-linking of alkene or alkyne bonds. Here, we report the first example of the chemical reconstruction of a 2D COF to a 3D COF with a complete lattice rearrangement facilitated by base-triggered boron hybridization. This chemical reconstruction involves the conversion of trigonal boronate ester linkages to tetrahedral anionic spiroborate linkages. This transformation reticulates the coplanar, closely stacked square cobalt(II) phthalocyanine (PcCo) units into a 3D perpendicular arrangement. As a result, the pore size of COFs expands from 2.45 nm for the initial 2D square lattice (sql) to 3.02 nm in the 3D noninterpenetrated network (nbo). Mechanistic studies reveal a base-catalyzed boronate ester protodeboronation pathway for the formation of the spiroborate structure.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
(a) Transformation of 2D BPDA-COF to 3D SPB-COF-DEA in N,N-diethylformamide (DEF). (b) Transformation of the boronate ester model compound m-BE-BPDA to the spiroboronate-linked m-SPB-DEA. Reaction conducted in DEF at 120 °C for 3 days. (c) Single crystal structure of m-SPB-DEA. The pink tetrahedra represent the spiroborate linkage.
Figure 2
Figure 2
(a) PXRD comparison between BPDA-DEF-X and the simulated pattern based on the corresponding 2D boronate ester (BPDA-COF) and 3D spiroborate (SPB-COF-DEA) crystal models. Diffraction peaks corresponding to the 3D phase are marked by gray dashed lines. BPDA-DEF-X, X = 3, 7, 10, 15, 30, and 40, represents the isolated product by reaction between (OH)8PcCo and BPDA in DEF at 120 °C for 3, 7, 10, 15, 30, and 40 days, respectively. (b) FTIR spectra comparison between BPDA-DEF-X and 2D BPDA-COF (bottom) and 3D SPB-COF-DEA (top) references. (c, d) Experimental PXRD pattern (red), profile calculated from Pawley fitting (black) showing the residual (blue), compared with the pattern simulated from the structural model (purple) for as-synthesized BPDA-DEF-3 and BPDA-DEF-40, respectively. Reflection positions are shown by tick marks. *The wide peak at the 2θ range of 15°–25° in (d) was due to solvent inclusion within the sample during PXRD measurement.
Figure 3
Figure 3
N2 sorption isotherms and pore size distribution for BPDA-DEF-3 (a, b) and BPDA-DEF-40 (c, d), respectively. Insets of (b) and (d) are the structural topology of the two COFs with pore represented by yellow balls. *The diameter of the yellow balls does not accurately represent the pore size.
Figure 4
Figure 4
(a) Proposed spiroborate formation mechanism. (b) 11B NMR of m-SPB-DEA reference material (top), boric acid (bottom); the reaction mixture after m-BE-BPDA and BPDA reacted in DEF at 120 °C for 3 days, including 11B NMR of the crystal precipitated from boric acid reaction system. *The signal marked with an asterisk at around 30.00 ppm is in good agreement with pristine BPDA. (c) Single crystal structure of the [BO4]− borate salt, generated by subjecting boric acid (B(OH)3) in DEF. C, H, O, B, and N are labeled in gray, white, red, pink, and blue.
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