Science & Technology (Commonwealth Union) – The use of “smart” materials that include thermochromic pigments, medical tools, hydorgels and more show great promise.
Materials that are “smart,” i.e., able to change their physical properties upon an application of external triggers such as light, heat, pressure, or magnetic and electric fields, are attracting increasing attention. Magnetism, which is determined by the electronic spin states of atoms, is one of the important properties that can be tuned in this way. In some metal complexes these spin states can switch between magnetic and non-magnetic states depending on environmental factors like temperature, light or mechanical stress.
In two recent studies, Abhishek Mondal, Associate Professor at the Solid State and Structural Chemistry Unit (SSCU) at the Indian Institute of Science (IISc), and his research group have developed new chemical frameworks made of self-organising metal–organic layers. These highly porous crystalline structures can reversibly switch their magnetic behaviour, offering promising potential for future data storage technologies, quantum computing systems, and high-performance industrial sensors.
The first study, published in Angewandte Chemie, addresses a long-standing issue in materials science: enabling strong, coordinated magnetic switching in three-dimensional, honeycomb-like porous materials commonly used for detecting gases and liquids. When a gas or liquid enters or exits these structures, the crystal framework expands or contracts, triggering changes in the spin states of the atoms. However, in conventional porous materials, this structural response is often weak and localised because the forces generated by individual atoms are absorbed by surrounding pores rather than transmitted through the entire lattice. As a result, the material fails to undergo a unified, system-wide change, reducing its effectiveness in sensing applications.
To solve this, Mondal’s team engineered a new compound that combines high porosity with an elastic structural network. In this design, when atoms undergo spin changes, the mechanical force they generate is efficiently transferred across the flexible lattice. This creates a cascading, domino-like effect that synchronises the entire material into switching its magnetic state—a process known as cooperative behaviour. Importantly, this magnetic transformation is fully reversible, allowing the material to be reused multiple times. The spin-state switching can also be triggered not only by pressure, but by light and heat as well.
Mondal indicated that they are at present engaged in scaling up the complex to design smart gas-capture sensors that have the ability to selectively adsorb industrially critical gases that include CH4, CO and CO2 with supreme sensitivity.
Although these materials show strong promise for environmental and biological sensing, their practical use has been limited by the temperatures required for them to function.
Krishna Kaushik, PhD student at SSCU and first author of both studies indicated that their goal was to synthesise a chemical system that exhibits these transitions near ambient temperatures.
Kaushik further pointed out that contemporary materials often operate only at ultra-low temperatures below 50 K (-223°C) and they are highly volatile and relax back to their ground state with even a slight rise in temperature.
Maintaining such extremely cold environments requires energy-intensive and expensive cooling systems.
To overcome this challenge, in a separate study published in Small, the team developed a two-dimensional hexagonal framework capable of light-, heat- and solvent-driven magnetic transitions close to room temperature. They began by creating a precursor complex which, when left in solution, interacts with surrounding solvent molecules and atmospheric moisture, gradually converting into a new, highly stable structure. The original network undergoes spin and electronic switching at a low temperature of 176 K (about -97°C), but after transformation, the resulting complex displays two distinct transitions at approximately 240 K and 310 K (around -33°C and 37°C). This effectively brings magnetic switching into the room-temperature range. The transition is also accompanied by a noticeable colour change, providing a clear visual signal that can be observed directly with the naked eye.
“Although these discoveries are still at the fundamental research stage, they address important global challenges,” added Mondal.
