Polyoxometalate Anion-Induced On–Off Spin-Crossover Property in Two Isomeric Cobalt(II) Complexes with Proton Conductivity

The integration of polyoxometalate (POM) anions with functionalized cations within a single molecule remains a challenging task, even though POMs have garnered significant interest over an extended period. Here, we constructed two cobalt(II) complexes by incorporating isomeric POM anions with [Co(pyterpy)2]2+. Intriguingly, a locked high-spin (HS) state and a spin-crossover (SCO) behavior of the 3d7-CoII ion in the identical cation [Co(pyterpy)2]2+ were governed by α-type and β-type [Mo8O26]4- anions, and the HS-Co(II) ion showed field-induced slow magnetic relaxation. Furthermore, both complexes exhibited potential as solid-state proton conductors. This study revealed that POM anions possessed the dual capability of modulating magnetism and synthesizing multifunctional molecular materials.