Gas-responsive porous magnet distinguishes the electron spin of molecular oxygen

Gas-sensing materials are becoming increasingly important in our society, requiring high sensitivity to differentiate similar gases like N(2) and O(2). For the design of such materials, the driving force of electronic host-guest interaction or host-framework changes during the sorption process has commonly been considered necessary; however, this work demonstrates the use of the magnetic characteristics intrinsic to the guest molecules for distinguishing between diamagnetic N(2) and CO(2) gases from paramagnetic O(2) gas. While the uptake of N(2) and CO(2) leads to an increase in T(C) through ferrimagnetic behavior, the uptake of O(2) results in an O(2) pressure-dependent continuous phase change from a ferrimagnet to an antiferromagnet, eventually leading to a novel ferrimagnet with aligned O(2) spins following application of a magnetic field. This chameleonic material, the first with switchable magnetism that can discriminate between similarly sized N(2) and O(2) gases, provides wide scope for new gas-responsive porous magnets.