Electronic structure investigations on triphenylphosphine (PPh3) ligated gold clusters are commonly carried out with model phosphine ligands. To explore the validity and the limitations of this approach, we have studied the effects of phosphine substituents in a series of gold(1) compounds: MeAuPR3, R = H, Me, Ph. We used the recently developed scalar-relativistic version of the linear combination of Gaussian-type orbitals (LCGTO) local density functional (LDF) method which allows an all-electron treatment of all systems under study. For structural properties the PH3 ligand provides a satisfactory model of the full PPh3 ligand. But the trimethylphosphine ligated models have to be employed if good agreement is desired for energy properties and for the dipole moment.
Discrete variational local density functional (Xa) calculations on the model complexes [(RN)U(NR,),] ( R = H (l), SiH, (2))have been performed in order to investigate the electronic structure of uranium amido/imido complexes. Special emphasis is placed on the energy ordering of the highest lying levels formed by U 5f orbitals and by out-of-plane N 2p, orbitals. Orbital relaxations are also estimated by studying the fragments N R and NR2 with R = H and R = SiMe, in order to allow a comparison of the model compounds 1 and 2 with the measured photoelectron spectrum of the complex ((Me,SiN)U[N(SiMe,),],). The ionization energies corresponding to the N 2p, MOs are calculated in the order N 2p, (amido) < N 2p, (imido). The calculated level ordering is rationalized by comparing the order of the two types of U-N bonds and the charge distributions of the corresponding ligands. Taking the calculated ordering as well as the character of the molecular orbitals into account, a new assignment of the observed photoelectron spectra is given based on a comparison of He I and He I1 spectra.
IntroductionThis work was carried out in order to investigate the bonding in complexes containing multiple bonds between uranium and the fmt-row elements.'-5 Uranium-xrbon multiple bonds have been described as primarily ionic on the basis of the U-C bond lengths, although thxe is mention of considerable T overlap between uranium and carbon in at least one complex.6 Uranium imido complexes show both and linear's8 U-N-R geometry, and it is not clear whether this is the result of simple crystal packing forces, as is claimed to be the case for linear and bent imido groups in [ O S O~( N C M~~)~] ,~ or whether it has an electronic origin, as in the case of main group imide complexes such as R3P=NR'.'0 In a recent photoelectron study of a number of uranium(V) imido complexes, uranium 5f and nitrogen 2p, ionization potentials were measured, and shifts in the values between different compounds were interpreted in terms of changes in the bonding in the compounds." It was the purpose of the present study to calculate the electronic structure of such complexes to provide further information about the nature of the bonding in them and to check the assignments of peaks in t h e photoelectron spectra.Discrete variational (DV) local density functional (LDF) calculations were carried out on the complexes [(HN)U(NH2),]
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