Department of Chemistry and Molecular Design Institute, New York University , 100 Washington Square East, New York, New York 10003-6688, United States.
Acc Chem Res. 2016 Dec 20;49(12):2669-2679. doi: 10.1021/acs.accounts.6b00360. Epub 2016 Sep 30.
Low-density molecular host frameworks, whether equipped with persistent molecular-scale pores or virtual pores that are sustainable only when occupied by guest molecules, have emerged as a promising class of materials owing to the ability to tailor the size, geometry, and chemical character of their free space through the versatility of organic synthesis. As such, molecular frameworks are promising candidates for storage, separations of commodity and fine chemicals, heterogeneous catalysis, and optical and electronic materials. Frameworks assembled through hydrogen bonds, though generally not stable toward collapse in the absence of guests, promise significant chemical and structural diversity, with pores that can be tailored for a wide range of guest molecules. The utility of these frameworks, however, depends on the resilience of n-dimensional hydrogen-bonded motifs that serve as reliable building blocks so that the molecular constituents can be manipulated without disruption of the anticipated global solid-state architecture. Though many hydrogen-bonded frameworks have been reported, few exist that are amenable to systematic modification, thus limiting the design of functional materials. This Account reviews discoveries in our laboratory during the past decade related to a series of host frameworks based on guanidinium cations and interchangeable organosulfonate anions, in which the 3-fold symmetry and hydrogen-bonding complementarity of these ions prompt the formation of a two-dimensional (2-D) quasi-hexagonal hydrogen-bonding network that has proven to be remarkably resilient toward the introduction of a wide range of organic pendant groups attached to the sulfonate. Since an earlier report in this journal that focused primarily on organodisulfonate host frameworks with lamellar architectures, this unusually persistent network has afforded an unparalleled range of framework architectures and hundreds of new crystalline materials with predictable solid-state architectures. These range from the surprising discovery of inclusion compounds in organomonosulfonates (GMS), as well as organodisulfonates (GDS), structural isomerism reminiscent of microstructures observed in soft matter, a retrosynthetic approach to the synthesis of polar crystals, separation of molecular isomers, storage of unstable molecules, formation of a zeolite-like hydrogen-bonded framework, and postsynthetic pathways to inclusion compounds through reversible guest swapping in flexible GS frameworks. Collectively, the examples described in this Account illustrate the potential for hydrogen-bonded frameworks in the design of molecular materials, the prediction of solid-state architecture from simple empirical parameters, and the importance of design principles based on robust high dimensional networks. These and other emerging hydrogen-bonded frameworks promise new advanced materials that capitalize fully on the ability of materials chemists to manipulate solid-state structure through molecular design.
低维分子主体框架，无论是具有持久分子尺度孔还是仅在被客体分子占据时可持续的虚拟孔，由于能够通过有机合成的多功能性来调整其自由空间的大小、形状和化学性质，已成为一类很有前途的材料。因此，分子框架是储存、商品和精细化学品的分离、多相催化以及光学和电子材料的有前途的候选材料。尽管通过氢键组装的框架通常在没有客体的情况下不稳定，但它们具有很大的化学和结构多样性，并且可以为广泛的客体分子定制孔。然而，这些框架的实用性取决于作为可靠构建块的 n 维氢键基序的弹性，以便可以在不破坏预期的整体固态结构的情况下操纵分子成分。尽管已经报道了许多氢键框架，但可进行系统修饰的框架很少，从而限制了功能材料的设计。本综述回顾了我们实验室在过去十年中与一系列基于胍阳离子和可互换的有机磺酸盐阴离子的主体框架相关的发现，其中这些离子的 3 重对称性和氢键互补性促使形成二维（2-D）准六边形氢键网络，该网络对引入广泛的附着在磺酸盐上的有机侧基具有很强的抵抗力。自该期刊早些时候的一篇主要关注具有层状结构的有机二磺酸盐主体框架的报道以来，这种异常持久的网络提供了无与伦比的框架结构和数百种具有可预测固态结构的新结晶材料。这些范围从在有机单磺酸盐（GMS）以及有机二磺酸盐（GDS）中发现包含物的惊人发现，到类似于软物质中观察到的微观结构的结构异构体，再到极性晶体合成的反合成方法、分子异构体的分离、不稳定分子的储存、沸石型氢键框架的形成以及通过灵活 GS 框架中可逆客体交换的后合成途径到包含物的形成。总的来说，本综述中描述的例子说明了氢键框架在设计分子材料方面的潜力、从简单经验参数预测固态结构以及基于稳健高维网络的设计原则的重要性。这些和其他新兴的氢键框架有望为充分利用材料化学家通过分子设计来操纵固态结构的能力的新型先进材料铺平道路。
