Ferroelectric and Spin Crossover Behavior in a Cobalt(II) Compound Induced by Polar-Ligand-Substituent Motion

Ferroelectric spin crossover (SCO) behavior is demonstrated to occur in the cobalt(II) complex, [Co(FPh-terpy)(2)](BPh4)(2)3ac (13 ac; FPh-terpy=4 '-((3-fluorophenyl)ethynyl)-2,2 ':6 ',2 ''-terpyridine) and is dependent on the degree of 180 degrees flip-flop motion of the ligand's polar fluorophenyl ring. Single crystal X-ray structures at several temperatures confirmed the flip-flop motion of fluorobenzene ring and also gave evidence for the SCO behavior with the latter behavior also confirmed by magnetic susceptibility measurements. The molecular motion of the fluorobenzene ring was also revealed using solid-state F-19 NMR spectroscopy. Thus the SCO behavior is accompanied by the flip-flop motion of the fluorobenzene ring, leading to destabilization of the low spin cobalt(II) state; with the magnitude of rotation able to be controlled by an electric field. This first example of spin-state conversion being dependent on the molecular motion of a ligand-appended fluorobenzene ring in a SCO cobalt(II) compound provides new insight for the design of a new category of molecule-based magnetoelectric materials.

Automated summary

The article investigates the ferroelectric spin crossover behavior in a cobalt(II) complex and finds that the flip-flop motion of the fluorophenyl ring can affect the spin state conversion. Confirmation of this effect is provided through single crystal X-ray structures, magnetic susceptibility measurements, and solid-state NMR spectroscopy.