Nickel Complex’s Magnetic Switch

With a turntable-like design, chemists have developed the first single molecule that can stably switch magnetic properties at room temperature in a homogeneous solution (Science, DOI: 10.1126/ science.1201180). This kind of spin-switching behavior had previously been limited to bulk materials or to very low temperatures, which limits potential applications in areas such as single-molecule magnetic storage. The switchable molecule, designed by Rainer Herges and coworkers at the University of Kiel, in Germany, is a nickel(II) porphyrin complex with a dangling phenylazopyridine group attached to its side. When exposed to green light, the nitrogen-nitrogen double bond in the phenylazopyridine isomerizes from trans to cis, which leaves the pyridine nitrogen hanging above the nickel like a record player needle. As the nitrogen coordinates to nickel, the complex’s geometry transitions from square planar to square pyramidal and its magnetic properties switch from diamagnetic to paramagnetic. The shift can be reversed by blue light. The team notes that the complex may be useful as a contrast agent that can be turned on and off at will for dynamic magnetic resonance imaging.