On the structure of lead(II) complexes in aqueous solutions.: II -: Tetranuclear clusters

Using the semiempirical MNDO method of quantum chemistry, optimum geometries and corresponding electronic structures of [Pb-4(OH)(4)](4+) model systems as well as of their hydrated [Pb-4(OH)(4)(H2O)(4)](4+) analogues were investigated. Stable tetranuclear lead(II) complexes present in aqueous solutions correspond to tetrahedro-Pb-4(mu(3)-OH)(4)(4+), cyclo-[Pb(mu(2)-OH)](4)(4+), Pb(mu(2)-OH)Pb(mu(2)-OH)(2)Pb(mu(2)-OH)Pb4+, Pb(mu(2)-OH)(2)Pb(mu(2)-OH)Pb(mu(2)-OH)Pb(mu(2)-OH)Pb4+, Pb(mu(2)-OH)-cyclo-[Pb(mu(2)-OH)](3)(4+) Pb(mu(2)-OH)Pb[(mu(2)-OH)Pb](2)(4+) or Pb(OH)(mu(2)-OH)Pb[(mu (2)-OH)Pb](2)(4+). The key role of mu(2)-OH and mu(3)-OH bridges (due to vanishing direct Pb-Pb bends) for the stability of the isomers is discussed. Our results do not confirm the assumption of preferential tetrahedral configuration of Pb-4(OH)(4)(4+) based on experimental studies. (C) 1999 Elsevier Science Ltd. All rights reserved.