CAREER: Studies of Chalcogen Bonding-Mediated Assembly towards Porous Crystalline Frameworks, Hierarchical Assemblies, and Multicomponent Materials

Colorado School Of Mines, Golden CO

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Non-Technical Abstract: Discoveries of new materials have led to seismic advances in our societies. These advances typically occur through breakthroughs with one of two key components of materials: the repeating individual molecular or atomic building block or the way individual components are connected. Such materials can be considered analogous to a brick wall, with the bricks as the repeating blocks, and the mortar connecting them together. While an enormous diversity of building blocks is known, only a handful of established modes of connectivity exist. Generally, each different mode of connectivity allows the creation of an entirely new class of materials. Perhaps the best example for this is the field of nanoporous frameworks, which are sponge-like materials containing voids slightly larger than individual molecules. Nanoporous frameworks containing similar bricks, but connected through different mortars, show vastly different behaviors, each type exhibiting a unique combination of properties. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, the principal investigator and their research group develop a new class of nanoporous frameworks enabled by a recently discovered mode of connectivity. In doing so, the principal investigator advances our knowledge of connectivity in materials, particularly by advancing the understanding of this nascent connectivity, realizing unparalleled structural complexities in materials, and developing a class of materials with a hitherto unseen set of properties. To help teach the core concepts of how building blocks assemble into materials, the investigators also develop and disseminate an inexpensive and highly modular model kit exercise. This level-adaptable game uses multi-colored modeling clay and toothpicks to teach students how the bricks and mortar work together to form materials. To reduce inequalities in upper-division chemistry offerings between research universities and primarily undergraduate institutions (PUIs), the principal investigator develops and offers a hybrid upper-division Physical Organic course that is simultaneously taught face-to-face at Colorado School of Mines and remotely to students at institutions across Colorado. Technical Abstract: The manner of bonding between constituent atoms or molecules invariably influences the properties of materials. Perhaps no material family is more emblematic of this than synthetic porous frameworks, wherein the properties, and thus utility, of a given subclass rely heavily on the directionality, dynamic reversibility, and net strength of the intermolecular interactions used. Therefore, the discovery and characterization of alternative modes of intermolecular assembly that may give rise to complementary material classes are of great interest. The primary objective of this project is to explore if chalcogen bonding, a recently defined non-covalent interaction, can deliberately and reliably assemble molecular tectons into low-density crystalline framework materials, towards the realization of a new class of frameworks: Chalcogen-Bonded Organic Frameworks, i.e. ChOFs. Empirical and computational studies of chalcogen bond-mediated assembly in model systems establish a set of quantitative guidelines for the rational design of permanently porous ChOFs with topologies predictively assembled from the molecular tecton structure and crystallization conditions. These insights lead to compositionally hierarchical and ordered multi-component materials, elusive features in established framework classes. Solution-phase association studies, such as NMR spectroscopy and ITC, and DFT-based calculations are used to quantify chalcogen bonding between synthesized tectons; the atomic structure of assembled frameworks is characterized by single-crystal XRD. An inexpensive and highly modular model kit exercise using modeling clay and toothpicks is developed and disseminated to students with the intent to teach core concepts of molecular assembly and crystal engineering. To reduce inequalities in upper-division chemistry offerings between research universities and PUIs, the principal investigator develops and offers a hybrid upper-division Physical Organic course that is simultaneously taught face-to-face at Colorado School of Mines and remotely to students at institutions across Colorado. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.