Exploring the thermochromism of sulfite-embedded polyoxometalate capsules

Abstract

The Dawson-type polyanion [α-Mo18O54(SO 3)2]4-, with two SO32- templates embedded inside a polyoxomolybdate(vi) cage, exhibits thermochromism over an exceptionally wide temperature range (∼500 K). The temperature dependence of the cluster structure, established from X-ray crystallography, IR and Raman spectroscopy and DFT calculations, is related to a decreasing HOMO-LUMO gap in the near UV with increasing temperature. We postulate this is due to geometrical changes that affect both the occupied and unoccupied frontier molecular orbitals of this cluster anion.