Among various chiral compounds, amide derivatives modified from amino acids are attractive chiral synthons in the synthesis of homochiral metal–organic frameworks. Herein, a pair of proline derivatives, (S)-1-(4-carboxybenzoyl) pyrrolidine-2-carboxylic acid ((S)-H₂PCA) and (R)-1-(4-carboxybenzoyl) pyrrolidine-2-carboxylic acid ((R)-H₂PCA), were designed and synthesized through incorporating a proline unit into 1,4-dicarboxybenzene. Under solvothermal conditions, (S)-H₂PCA and (R)-H₂PCA further reacted with 4,4′-bipyridine (4,4′-BIP), Cu(II) and Co(II) ions to obtain four enantiomeric compounds, [Cu((S)-PCA)(4,4′-BIP)]·DEF·H₂O(1-L), [Cu((R)-PCA)(4,4′-BIP)]·DEF·H₂O(1-D), [Co((S)-PCA)(4,4′-BIP)]·1.5H₂O (2-L) and [Co((R)-PCA)(4,4′-BIP)]·1.5H₂O (2-D) (DEF = N,N-diethyl formamide). Although all compounds have pillared-layer frameworks with 6-connected pcu nets, their structural motifs are still very different. The frameworks of 1-L and 1-D are non-interpenetration structures containing two kinds of helical chains, while 2-L and 2-D are 2-fold interpenetration frameworks with only one kind of helical chain. Furthermore, their solid-state CD spectra, semi-conductive properties and photocatalytic behaviors were also investigated. The present work provides a promising method to design and synthesize homochiral MOFs with helical structures through semirigid (S)-H₂PCA and (R)-H₂PCA.

中文翻译：

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基于对映异构脯氨酸衍生物的半螺旋螺旋手性金属-有机骨架

在各种手性化合物中，从氨基酸修饰的酰胺衍生物在同手性金属-有机骨架的合成中是有吸引力的手性合成子。在此，一对脯氨酸衍生物，（S）-1-（4-羧基苯甲酰基）吡咯烷-2-羧酸（（S）-H ₂ PCA）和（R）-1-（4-羧基苯甲酰基）吡咯烷-2-通过将脯氨酸单元掺入1,4-二羧基苯中来设计和合成羧酸（（R）-H ₂ PCA）。在溶剂热条件下，（S）-H ₂ PCA和（R）-H ₂ PCA进一步与4,4'-联吡啶（4,4'-BIP），Cu（II）和Co（II）离子获得四种对映体化合物，[Cu（（S）-PCA）（4,4'-BIP）]·DEF·H ₂ O（1 -L），[Cu（（R）-PCA）（4 ，4'-BIP）]·DEF·H ₂ O（1 -D），[Co（（S）-PCA）（4,4'-BIP）]·1.5H ₂ O（2 -L）和[Co （（R）-PCA）（4,4'-BIP）]·1.5H ₂ O（2- D）（DEF ＝N，N-二乙基甲酰胺）。尽管所有化合物都具有带有6个连接pcu网的柱状层骨架，但它们的结构基序仍然非常不同。1 -L的框架和1 -D是含有两种螺旋形的链的非互穿结构，而2 -L和2 -D是仅具有一种螺旋链的2倍穿插框架。此外，还研究了它们的固态CD光谱，半导体性质和光催化行为。本工作提供了一种通过半刚性（S）-H ₂ PCA和（R）-H ₂ PCA设计和合成具有螺旋结构的同手性MOF的有前途的方法。