Taming Reactive Molecular Magnets

The elusive molecular magnet, m-xylylene (bottom, left), was synthesised in-situ and investigated using photoelectron spectroscopy.

Aromatic diradicals possess fascinating properties and offer a wide range of potential applications from quantum chemistry to materials science. Indeed, the high spin character makes these species ideal model systems to study the properties of molecular magnets or magnetic organic frameworks. Among diradicals, meta-xylylene is one of the most interesting, albeit elusive, system thanks to its electronic structure. This is owing to its triplet electronic ground state, which is unique for the meta isomer as the ortho and para ones are closed shell species with singlet character.

Due to the high spin, the reactivity of meta-xylylene is very high, its lifetime short and its preparation at ambient conditions fails completely. Researchers from the VUV beamline at SLS, ETH Zurich, Wollongong and Melbourne, Australia developed an inventive approach to generate and probe m-xylylene diradicals selectively by using flash vacuum pyrolysis of the stable diiodo precursor, m-C8H8I2. The pyrolysis source yielded m-C8H8 isomer-selectively in a molecular beam. Photoelectron photoion coincidence (PEPICO) spectroscopy was utilized to measure the photoelectron spectrum (PES) of the diradical and the fragmentation dynamics of the precursor. Using this approach, they elucidated electronic and vibrational features of m-C8H8, and derived thermochemical data including adiabatic ionization energies and enthalpies of formation.

The experiments suggest that multiplicity change of m-C8H8 in a substrate could dramatically alter the electronic and magnetic properties of a material, without necessarily affecting its structural features.