A Proton Conducting Cobalt(II) Spin Crossover Complex.

Spin crossover (SCO) complexes have been extensively explored as bistable materials and recently used as molecular modules for the development of new multifunctional molecular magnetic materials. Herein, we present the synthesis, crystal structure, magnetic, and electrical properties of a mononuclear cobalt complex constructed by a halogen-functionalized terpyridine derivative and organosulfonate. A complete and gradual spin transition with the T 1/2 =200 K was observed for the Co 2+ ions through both the magnetic measurement and dynamic crystallographic experiments. Interestingly, considerable room temperature proton conductivity of 6.9×10 -5  S cm -1 under 98% relative humidity was evidenced because of the presence of sulfonate-assisted hydrogen-bonded proton hopping pathways. The forgoing results not only provide an unprecedented proton-conducting cobalt(II) SCO complex but also a promising way for the design and construction of bifunctional SCO molecular conductors via the incorporation of SCO transition and proton conduction.