Theoretical studies of the effective exchange interactions and photoinduced magnetism in manganese and copper di(4-pyridyl)carbene complexes

UHF, UMPn (n = 2,4), UCC and DFT (UBLYP and UB3LYP) calculations using several basis sets were performed in order to elucidate the sign and magnitudes of the effective exchange interactions (J(ab)) of models of 1:1 complex of Mn(hfac)(2) or Cu(hfac)(2) with (4-pryidyl)methylene. The J(ab) value between Mn(II) and divalent carbon (:C) through 4-pyridyl group by the UMP and UCCSD(T)/triple-zeta basis set was antiferromagnetic, while it was ferromagnetic between Cu(II) and :C. This is wholly consistent with the experiments. The signs of J(ab) values are explained by mechanisms of spin-exchange couplings through the configuration interaction pictures. (C) 1999 Elsevier Science B.V. All rights reserved.