Obtaining Chiral Metal–Organic Frameworks via a Prochirality Synthetic Strategy with Achiral Ligands Step-by-Step

Abstract

Although some achievements of constructing chiral metal-organic frameworks (MOFs) with diverse achiral ligands have been made, there is still a lack of full understanding of the origin and formation mechanism of chirality, as well as the reasonable principles for the design and construction of chiral frameworks. The concept of prochirality in organic molecules and complex systems inspires us to explore the synthetic strategy of chiral MOFs based on achiral sources. Here, an achiral compound [Cu(en)][(VO3)2] (1) was isolated in the CuCl2/NH4VO3/en system, while further chiral frameworks [Cu(en)(Im)2][(VO3)2] (2a and 2b) were obtained by the reaction between compound 1 and another achiral ligand Im (ethanediamine = en and imidazole = Im). In the present system, compound 1 has the characteristic of a quasi-plane structure unit. Further reaction of compound 1 and the achiral ligand (Im) induced the formation of chiral Λ/Δ Cu centers, and then a pair of chiral frameworks containing one-dimensional (1D) helical chains was formed. The chiral symmetry breaking phenomenon of compounds 2a and 2b can also be expected and explained based on this kind of prochirality synthetic strategy.

Ion-Directed Synthesis of Indium-Derived 2,5-Thiophenedicarboxylate Metal–Organic Frameworks: Tuning Framework Dimensionality

“…35−39 Template-controlled MOF synthesis has been well studied and reviewed extensively. 40−45 In the synthesis of anionic MOFs, N-centered cations (ammonium ions) are often the template of choice, since they are chemically robust, are easily synthesized, 46−48 have the potential to be chiral, 49 can be strong hydrogen bond donors. Given the potential for diverse impacts of such cations on MOF synthesis, we hypothesized that a series of unique frameworks could be synthesized from the same starting inorganic and organic building blocks in which the structural outcome was controlled by changing the templating cation.…”

“…Since the [In­(O 2 CR) 4 ] − SBU is anionic, it is associated with charge-balancing cations deposited during the synthesis process, which are often themselves products of solvent decomposition. The role of such cations during MOF formation is not yet fully understood, but it is known that the type of cation can have a significant impact on pore architecture and diversity, leading to a potential template effect. − Template-controlled MOF synthesis has been well studied and reviewed extensively. − In the synthesis of anionic MOFs, N -centered cations (ammonium ions) are often the template of choice, since they are chemically robust, are easily synthesized, − have the potential to be chiral, − and can be strong hydrogen bond donors. Given the potential for diverse impacts of such cations on MOF synthesis, we hypothesized that a series of unique frameworks could be synthesized from the same starting inorganic and organic building blocks in which the structural outcome was controlled by changing the templating cation.…”

Monocarboxylic Acid Driven Structural Transformation in Manganese Based Metal–Organic Frameworks

“…Bulk chirality can be created in MOFs which exhibit a network topology that is inherently chiral because of the spatial organization of achiral building blocks. 32 But unfortunately, spontaneous resolution sometimes leads to the formation of racemic mixtures or conglomerates. 33 In the present work two compounds were crystallized with a chiral space group containing a 2 1 screw axis and they are optically inactive.…”

Viedma Ripening of Chiral Coordination Polymers Based on Achiral Molecules

“…Generally, CCPs could be obtained by introducing certain chiral agents to play as components, counterions, templates, or structural directing agents. − The limited species of commercial chiral agents and their high cost have hindered the development of CCPs. On the other hand, people have found that CCPs could also be prepared by adopting normal achiral starting materials, without any chiral agents (named a CCPs in the following discussion). − This phenomenon is usually called “spontaneous resolution”. However, the products of those a CCPs were always racemic mixture (conglomerates) or racemic solid solution, which makes the study of application difficult.…”