Theoretical investigation of iron carbide, FeC (original) (raw)

Accurate ab initio calculations of the ground states of FeC, FeC+, and FeC

Chemical Physics, 2010

For the ground states of the diatomic carbide FeC(X 3Δ) and its ions, FeC+(X 2Δ) and FeC-(X 2Δ), we report on accurate multireference variational ab initio results employing augmented correlation consistent basis sets of quintuple cardinality. The dissociation energies and bond lengths are found to be D00=87+/-1, 95.2, and 84+/-1 kcal/mol at re=1.581, 1.556, and 1.660 A˚ for FeC, FeC+, and FeC-, respectively. All our final numbers are in agreement with the available experimental data.

DFT Study of the Geometry and Energy Order of the Low Singlet and Triplet States of [d 4 -η 5 -CpMo(CO) 2 X] 16-Electron Complexes (X = Halogen, CN, H, and CH 3 )

Inorganic Chemistry, 2004

DFT methods have been used to investigate the dependence of the geometry and energy order of the low energy states of [d(4)-eta(5)-CpMo(CO)(2)X] 16-electron complexes on X (X = halogen, CN, H and CH(3)). The calculations use a double-zeta plus polarization valence basis set on all atoms and utilize relativistic ECPs on Mo and the heavier halogens. In every case two singlet and two triplet electronic states have been considered and minimized at the B3LYP level. For X = Cl, additional calculations were carried out at the BPW91, CCSD(T), and CASSCF levels. In the C(s) point group, the singlet states are from the (1a')(2)(1a'')(2) and (1a')(2)(2a')(2) configurations of the valence d(4) electrons of the metal, and are denoted (1)A'-a and (1)A'-b, respectively. The triplet species are for the lowest (3)A'' and (3)A' states from the (1a')(2)(2a')(1)(1a'')(1) and (1a'')(2)(1a')(1)(2a')(1) d(4) configurations. For all substituents, the geometry of both the singlet and triplet states is found to distort substantially from the uniform 3-leg piano-stool structural motif, a behavior that can be related to Jahn-Teller effects. When X is a halogen or a methyl, (1)A'-b is predicted to be lower than (1)A'-a, while the reverse order of these two singlet states is calculated for X = H and CN. For all substituents (3)A' is substantially higher than (3)A''. In turn, the energy of (3)A'' is calculated to be comparable to the lower singlet state of each complex. Attempts are made to rationalize some of these results using qualitative MO theory.