The cis / trans conformation approach for tuning the magnetic coupling in a diradical: isolation of pure pyridine-based diradical dianions.

Two-electron reductions of 3,3'-bis(2,6-dimesitylpyridin-4-yl)-1,1'-biphenyl 1 with elemental potassium in the absence and presence of 18-c-6 afforded the diradical dianion salts [K + ] 2 ˙[ trans -1]˙˙ 2- and [K(18-c-6)] + 2 ˙[ cis -1]˙˙ 2- , which exhibit trans and cis configurations, respectively. The transoid conformer could be converted to the cisoid one through reacting with 18-c-6.