Monitoring the Substrate‐Induced Spin‐State Distribution in a Cobalt(II)‐Salen Complex by EPR and DFT

Ground state changes of (R,R’)‐N,N’‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexane‐diamino Co(II), following coordination of various pyridyl substrate has been examined by CW EPR, pulsed relaxation measurements and DFT. The solution‐based Co(II) complex possesses a low spin (LS) state yz,2A2⟩ (with g‐values of 1.96, 1.895, 3.14). Upon coordination of the pyridyl substrate, the resulting bound adduct reveals a distribution of LS ‘base‐on’ species, possessing a z2,2A1⟩ electronic ground state (with g‐values of 2.008, 2.2145, 2.46) and a high spin (HS) species (with geff=4.6). DFT indicated that the energy gap between the LS and HS state is dramatically lowered (ΔE