3D Covalent Organic Frameworks Selectively Crystallized through Conformational Design

We
present a strategy whereby selective formation of imine covalent
organic frameworks (COFs) based on linking of triangles and squares
into the fjh topology was achieved by the conformational
design of the building units. 1,3,5-Trimethyl-2,4,6-tris­(4-formylphenyl)­benzene
(TTFB, triangle) and 1,1,2,2-tetrakis­(4-aminophenyl)­ethene (ETTA,
square) were reticulated into [(TTFB)4­(ETTA)3]imine, termed COF-790, which
was fully characterized by spectroscopic, microscopic, and X-ray diffraction
techniques. COF-790 exhibits permanent porosity and a Brunauer–Emmett–Teller
(BET) surface area of 2650 m2 g–1. Key
to the formation of this COF in crystalline form is the pre-designed
conformation of the triangle and the square units to give dihedral
angles in the range of 75–90°, without which the reaction
results in the formation of amorphous product. We demonstrate the
versatility of our strategy by also reporting the synthesis and characterization
of two isoreticular forms of COF-790, COF-791 and COF-792, based on
other square building units.

本研究提出了一种策略，通过构建单元的构象设计，实现了基于三角形与正方形连接形成的 fjh 拓扑结构的亚胺共价有机框架（COFs）的定向构建。1,3,5-三甲基-2,4,6-三(4-甲酰苯基)苯（TTFB，三角形）和1,1,2,2-四(4-氨基苯基)乙烯（ETTA，正方形）通过交联形成[(TTFB)4(ETTA)3]亚胺，命名为COF-790，该框架通过光谱学、显微学和X射线衍射技术进行了全面表征。COF-790表现出永久的孔隙度和2650 m2 g–1的Brunauer-Emmett-Teller（BET）比表面积。该COF在晶体形式中的形成关键在于预先设计的三角形和正方形单元的构象，以提供75-90°的二面角，否则反应将导致无定形产物的形成。我们通过报道基于其他正方形构建单元的COF-790两种同构形式的合成与表征，展示了该策略的通用性。