Moderating the acidity of Pb(II)-water complexes through the coordination of nonaqueous ligands: a computational study.

The metal dication Pb(II) is known to promote catalytic cleavage of the sugar-phosphate backbone in tRNA. The mechanism proposed to achieve this step requires that the [Pb(II)OH(-)](+) moiety act as a nucleophile and alter the local acidity of surrounding water molecules. MP2 calculations investigating the effect that nonaqueous bases have on the stability of dihydrated-Pb(II) show that the height and position of the proton-transfer barrier are sensitive to the presence of a single N- or O-coordinating "spectator" ligand and that, with the addition of two ligands coordinated directly to the Pb(II) center, the equilibrium for the hydrolysis reaction can shift to the left, thus making the Pb(II)-hydrate complex more stable than the Pb(II)-hydroxide complex.

Reductive coupling of carbon monoxide by U(III) complexes--a computational study.

The role of U((η-C(8)H(6){Si(i)Pr(3)-1,4}(2))(η-C(5)Me(5)) and U((η-C(8)H(6){Si(i)Pr(3)-1,4}(2))(η-C(5)Me(4)H) in the reductive di- tri- and tetramerization of CO has been modelled using density functional methods and U(C(8)H(8))(C(5)H(5)) as the metal fragment. The orbital structure of U(C(8)H(8))(C(5)H(5)) is described. CO binding to form a monocarbonyl U(C(8)H(8))(C(5)H(5))(CO) is found, by a variety of methods, to place spin density on the CO ligand via back-bonding from the U5f orbitals.

Mechanistic studies on the reductive cyclooligomerisation of CO by U(III) mixed sandwich complexes; the molecular structure of [(U(eta-C8H6{Si(i)Pr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2).

The stoichiometric reaction of 1 equiv of CO with [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)] affords the linear diuranium ynediolate complex [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2) which does not react with further CO to give the deltate derivative [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta2-C3O3). Spectroscopic and computational studies suggest a plausible mechanism for the formation of the deltate complex, in which a "zig-zag" diuranium ynediolate species is the key intermediate.

Infrared multiphoton spectra from metal dication complexes in the gas phase.

Infrared multiphoton spectra have been recorded for the first time from metal dication complexes held in an ion trap. The photofragmentation of [M(pyridine)4]2+ complexes has been observed in the range 920-1090 cm(-1) and for M=Cu2+, Mg2+ and Zn2+. The narrow absorption features are identified as vibrational modes of the pyridine molecule and comparisons with calculations suggest that the Mg2+ and Zn2+ ion complexes have D2d (compressed tetrahedron) structures, and that the Cu2+ complex is probably square-planar (D4h).

Ligand field spectroscopy of Cu(II) and Ag(II) complexes in the gas phase: theory and experiment.

Ligand field spectra have been recorded in the gas phase for the two series of complexes containing either Cu(II) or Ag(II) in association with pyridine. Where comparisons are possible, the gas phase spectra match those recorded in the condensed phase; however, for Ag(II) systems the results differ in interpretation. The Ag(II) data are attributed to a ligand-to-metal charge transfer process, and the Cu(II) data (spectral region and extinction coefficient) match the characteristics of a d-d transition.