Thermal and light induced valence tautomerism in a samarium-pyrazine polymer

Valence tautomerism is a stimulated intramolecular electron transfer which allows for switching between two distinct redox isomers. Such compounds,
incorporating a redox-active ligand and a redox-active metal, allow for the realisation of switchable optical and magnetic materials. The first lanthanide containing
coordination polymer to exhibit this behaviour, SmI2(pyz)3, exhibits an abrupt, hysteretic transition between {Sm(II)-pyz} and {Sm(III)-pyz.-} tautomers. Alloying with other halides allows for tuning of the valence tautomeric "switching" temperature. Herein, we will utilise XANES and XMCD at the L2,3 edges of Sm alongside Sm-149 Mössbauer spectroscopy to probe the Sm valency and electronic configuration of the various tautomers formed after temperature change and light irradiation.