NSF Center for the Mechanical Control of Chemistry

Overview

What are the rules that govern mechanically driven reactions?  Can we measure them?  Can we control them sufficiently to direct specific reaction outcomes?  These are the basic questions at the heart of the research conducted within the CMCC.

The current state-of-the-art in mechanochemical synthesis is not much more sophisticated than mixing reactants together and hitting them with a hammer.  While it has become apparent from the last few decades that you can hit a surprising amount of things with a hammer to create seemingly limitless chemical products, prediction is significantly limited.  What happens if someone hits the reactants harder or softer, hits them head on or with glancing blows, hits them once or millions of times?  And if these parameters matter, can we even make a hammer that can control them?


The CMCC has set about to begin to answer these questions through two research thrusts: 1) Pericyclic reactions and 2) perovskite synthesis.  Inter-connected with these thrusts is the research and development of a bold suite of experimental and computational tools that are essential to unlocking the secrets of mechanically driven reactivity.

Integrated Toolset Program

The current state-of-the-art in mechanochemical synthesis is not much more sophisticated than mixing reactants together and hitting them with a hammer.

The experimental methods to be employed and developed will involve hybrid surface analytical tools that will have the capacity to exert precisely-controlled forces, measure the influence of force on reaction kinetics, probe atomic-scale through mesoscale structures, and monitor surface chemical changes and product distributions from force-driven reactions. The suite of experimental tools span the length and time scales needed to study force-driven surface chemical reactions in well-controlled environments encompassing vacuum, gas, and liquid, and will enable the design of scaled-up of next generation mechanochemical reactors with control over reaction rates and product selectivity.

Pericyclic Reactions

No predictive guidance exists for reactions under strain or compression.

Peri-cyclic reactions are governed by the Woodward-Hoffmann rules that dictate whether a reaction is thermally or photochemically allowed based on orbital symmetry arguments. No such similar predictive guidance, however, exists for these reactions under strain or compression.  Here, we will explore various reversible pericyclic reactions on surfaces with an initial focus upon two sets of conditions that are designed to disentangle the various mechanisms by which force influences reaction energetics.

The first involves studying bond-forming reactions on atomically-precise membranes, where the substrate bonds will be strained in a controlled fashion and their reactivity studied, where our hypothesis is that the bonds under strain in these materials become more chemically reactive due to their reduced bond-order.

In the second, reactive species (e.g. dienes, dienophiles, azides, alkynes, etc.) are corralled in self-assembled monolayers and their orientation with respect to the external force is controlled.  The ultimate goal of this work is to develop Woodward-Hoffmann style rules that govern mechanochemical selectivity.

Perovskite Synthesis and Phase Transformations


Many minerals take the perovskite structure, formed under high pressure beneath the earth’s surface.

The simplicity of the chemical formula of perovskites, ABX3, belies their astonishing diversity of structures and properties. Many minerals take the perovskite structure, formed under high pressure beneath the earth’s surface, highlighting the promise of mechanochemical synthesis as a driver of perovskite materials design.  Partial occupancy of cation sites (“perovskite alloys”), as well as point and extended defects, lead to dramatic changes in properties, resulting in their exploration as semiconductors for photovoltaic energy conversion, photocatalytic water splitting reactivity, ferroelectricity and piezoelectricity, multiferroicity, and high-temperature superconductivity. Our primary goal is to understand the potential of mechanochemical methods in perovskite synthesis and the discovery of novel perovskite forms.