Photoelectron spectroscopy of bis(2,4-pentanedione)-oxovanadium(IV) [VO(acac)(2)] and derivatives: substituent effects on the 2,4-pentanedione donor

The electronic structure of derivatives of VO(acac)(2) is probed using gas-phase UV-photoelectron spectroscopy [acac = 2,4-pentanedione]. The effect on the metal center of electron-donating and -withdrawing groups on the acac ligands is examined. Ionizations from metal-based, acac-based, and V=O-based orbitals are clearly observed. We find that changes at the ligand periphery lead to equivalent changes in the energies of the metal-based and ligand-based ionizations. Additionally, we find that a linear correlation exists between the ionization energies of the metalated complexes and the pK(a) values of the free ligands, indicating that the pK(a) is a good indication of the overall electron-donating abilities of acac ligands.