Molecules that exhibit bistable physical states, which means they are capable of switching between two distinct states, show potential as elementary binary units for information storage. Transition metal complexes can display magnetic bistability by either spin-crossover or single-molecule magnet behavior.

An international team based in France and the USA and led by Jeffrey Long, University of California, Berkeley, CA, USA, have investigated the molecular salt [Fe(1-propyltetrazole)₆](BF₄)₂, which exhibits magnetic tristability. The complex can switch between two states either by spin-crossover or single-molecule magnet behavior. When the complex was held in a magnetic field incident light reversibly flipped the molecular switch between one of three states.

The team suggest that this phenomenon might be exploited in ternary information storage systems that have the possibility of being 0,1, or 2 in value and so offering much higher information densities than bistable molecules that are either 0 or 1.

• Tristability in a Light-Actuated Single-Molecule Magnet,
  Xiaowen Feng, Corine Mathonière, Ie-Rang Jeon, Mathieu Rouzières, Andrew Ozarowski, Michael L. Aubrey, Miguel I. Gonzalez, Rodolphe Clérac, Jeffrey R. Long,
  J. Am. Chem. Soc. 2013.
  DOI: 10.1021/ja407332y