Quantum chemical study of the geometric and electronic structure of the FeC2 molecule

The FeC2 molecule in its different geometric conformations and electronic s tates has been studied using the DPT (B3LYP) and CASSCF/CASPT2 methods. Bot h approaches predict the cyclic (C-2 upsilon) structure to be more stable t han the linear (C-infinity upsilon) conformation. The ground state has been found to be a quintet, which can be formally regarded as an ionic Fe2+-C-2 (2-) complex, with two 4s electrons of Fe transferred to the C-2 ligand and the remaining six valence electrons distributed among the split d orbitals . For the low-lying excited states of the C-2 upsilon conformation, there i s a good semi-quantitative agreement between the B3LYP and the CASPT2 resul ts. (C) 1999 Elsevier Science B.V. All rights reserved.