Gas phase photoelectron studies of organoplatinum complexes using helium I, helium II and synchrotron radiation.

摘要

Gas-phase He I and He II photoelectron spectra of four series of organoplatinum complexes are reported, together with synchrotron radiation photoelectron spectra of CpPtMe{dollar}sb3{dollar} (Cp = {dollar}etasp5{dollar}-C{dollar}sb5{dollar}H{dollar}sb5{dollar}) and PtMe{dollar}sb2{dollar} (COD) (COD = 1,5-cyclooctadiene). The platinum complexes investigated with both He I and He II sources include square-planar cis-dimethylplatinum(II), square-planar cis-bis(trifluoromethyl)platinum(II), half-sandwich ({dollar}etasp5{dollar}-cyclopentadienyl)trimethylplatinum(IV), and octahedral-like ({dollar}beta{dollar}-diketonato)trimethylplatinum(IV) complexes. The electronic structures of the complexes studied are discussed using the He I and He II spectral information, such as the ionization energy shifts from ligand substitutions and the resolved vibrational splittings from ligand-based orbitals, and using X{dollar}alpha{dollar}-SW calculations on some model compounds. The photo-ionization behaviour of the upper valence orbitals of CpPtMe{dollar}sb3{dollar} and Me{dollar}sb2{dollar}Pt(COD) is discussed in terms of the branching ratios as a function of the photon energies from 21 to 100 eV.; In the complexes cis- (PtMe{dollar}sb2{dollar}L{dollar}sb2{dollar}) and cis- (Pt(CF{dollar}sb3{dollar}){dollar}sb2{dollar}L{dollar}sb2{dollar}), the two molecular orbitals with the lowest ionization energies are assigned to Pt-ligand {dollar}sigma{dollar}-orbitals, and these are followed by four MO's which have mostly nonbonding Pt character. The Me contribution to the Pt-Me {dollar}sigma{dollar} bonds has essentially C 2p character, while the CF{dollar}sb3{dollar} contribution to the Pt-CF{dollar}sb3{dollar} bond is C-F antibonding with a significant C 2s character. The {dollar}sigma{dollar}-donor ability of a ligand L is reflected in its first ionization energy and the {dollar}pi{dollar}-acceptor ability of the ligand is reflected by the energy separation of the Pt 5d{dollar}sb{lcub}pi{rcub}{dollar} orbitals.; In the complexes CpPtMe{dollar}sb3{dollar} and Cp{dollar}sp*{dollar}PtMe{dollar}sb3{dollar} (Cp{dollar}sp*{dollar} = {dollar}etasp5{dollar}-C{dollar}sb5{dollar}Me{dollar}sb5{dollar}), the eight upper filled MO's are composed of three Pt 5d-based MO's unevenly sandwiched between the Pt-ligand orbitals. The ionization energies of the first six valence MO's fall in the order {dollar}pisb3{dollar}, {dollar}<{dollar} n {dollar}<{dollar} Pt-n{dollar}sb{lcub}+{rcub} <{dollar} Pt 5d, Pt-Me in the ({dollar}beta{dollar}-diketonato)trimethylplatinum(IV) complexes.; The differences in orbital character are generally reflected in the experimental branching ratios in the absence of resonance effects. A possible resonance resulting from a Pt-ligand {dollar}sigma{dollar} electron transition to an f-like antibonding orbital is observed in CpPtMe{dollar}sb3{dollar}.