Tristability Arising from Singlet−Triplet and Quartet Spin States for Dimeric Co^IISalen

The magnetic behavior of <i>N</i>,<i>N</i>′-ethylenebis(salicylideniminato)cobalt(II) (Co^IISalen, <b>1</b>) has been reinvestigated and reveals spin-crossover behavior above 295 K. It has a singlet ground state and a triplet excited state at 30 K (21 cm⁻¹; 60 cal/mol) above the ground state, and at a higher temperature spin crossover to the quartet, a second excited state occurs.