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 seve ral 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 betw een 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 ferromag netic 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 co uplings through the configuration interaction pictures. (C) 1999 Elsevier S cience B.V. All rights reserved.