Electronic structure and stability of transition metal acetylacetonates TM(AcAc)n (TM = Cr, Fe, Co, Ni, Cu; n = 1, 2, 3)

Electronic Structure of the Complete Series of Gas-Phase Manganese Acetylacetonates by X-ray Absorption Spectroscopy

“…Considering the small energy differences, these calculations do not provide a definitive assignment of the structure. In the following, we will discuss the square planar structure, also shown in Figure 1, that is in line with the ground-state structure of isoelectronic Cr(acac) 2 48,49 and proposed planar structure for other 3d 4 metal−ligand complexes. 50 Changes in the electronic structure of both geometries are minor, and results for the distorted structure are shown in the Supporting Information.…”

“…In the Mn(acac) 1 + complex, the orbitals with strong 3d yz , 3 normald z 2 , and 3 normald x 2 − y 2 character group together within 0.2 eV being basically degenerate, while the 3d xy orbital is pushed up in energy by about 0.6 eV. This is expected from a simple CF picture where the 3d xy orbital has the highest density along the metal–oxygen bond. However, within the CF picture we would also expect the 3d xz orbital to group with the 3d yz , 3 normald z 2 , and 3 normald x 2 − y 2 orbitals but instead the DFT calculation predicts a strong hybridization of the 3d xz orbital with a ligand π* orbital resulting in the formation of bonding and antibonding molecular orbitals well separated in energy shifting the transitions related to the bonding and antibonding orbitals symmetrically down and up by about 0.6 eV, respectively.…”

“…The good agreement of calculated and experimental spectra allows us to identify the molecular orbitals involved in the individual transitions represented as sticks in Figure . However, we are focusing only on those molecular orbitals that are hybrids of ligand and metal (manganese) 3d valence states. , From the relative excitation energies into these molecular orbitals, we deduce an energetic ordering of the unoccupied 3d derived states as shown in Figure along with isosurface plots of the respective molecular orbitals. All other transitions shown in Figure are dominated by transitions into ligand type orbitals and are therefore omitted in Figure .…”

“…The molecule adopts a C 2v symmetry identical to the prediction of isoelectronic Cr(acac) 1 . 48 There are, however, slight differences in transition-metal−oxygen bond lengths that become shortened in Mn(acac) 1 + (1.900 Å) compared to Cr(acac) 1 (2.015 Å). Since the transition-metal monoacetylonates have not been stabilized in the condensed phase or as solvated species, there is no experimental data on the structure of Mn(acac) 1 + .…”

“…)) ground state for neutral Cr(acac) 1 . 48 Note that the electronic configuration of Mn(acac) 1 + does not change when adding the 4s orbital to the active space. The mono-configurational nature and the fact that the experimental spectrum can be reasonably well reproduced by a CF simulation only, implies that there is little ligand−metal or metal−ligand charge transfer and hybridization.…”