Understanding Lead Chemistry from Topological Insights: The Transition between Holo‐ and Hemidirected Structures within the [Pb(CO)_n]²⁺ Model Series

Abstract

In this contribution, we focus to the currently unknown [Pb(CO)(n)](2+) model series (n=1 to 10), a set of compounds which allows us to investigate in-depth the holo- and hemidirectional character that lead complexes can exhibit. By means of DFT computations performed using either relativistic four-component formalisms coupled to all-electron basis sets for [Pb(CO)](2+), [Pb(OC)](2+) and [Pb(CO)(2)](2+), or scalar relativistic pseudopotentials for higher n values, the structure and the energetics of these species are investigated. The results are complemented by Constrained Space Orbital Variations (CSOV) and Electron Localization Function (ELF) comprehensive analyses in order to get better insights into the poorly documented chemical fundamentals of the Pb(2+) cation. Whereas the discrimination between holo- and hemidirected structures is usually done according to the geometry, we here provide a quantitative indicator grounded on <rho>(V(Pb)), the mean charge density of the valence monosynaptic V(Pb) ELFic basin associated to the metal cation. Free-enthalpy relying discussions show, moreover, that those gas-phase complexes having n=7, 8 or 9 may be experimentally instable and should dissociate into [Pb(CO)(6)](2+) and a number of CO ligands. According to second-order differences in energy, it is anticipated that the n=3 or 6 structures should be the most probable structures in the gas phase. Gathering all data from the present theoretical study allows us to propose some concepts that the versatile structural chemistry of Pb(2+) complexes could rely on.

Structure of trimers of group-2B metal dihalides from relativistic density-functional calculations

“…The electron localisation function (ELF) connects Lewis's theory of valence to quantum chemical topology through the partition of the molecular space into adjacent non-overlapping basins [18][19][20][21]: these are the core basins surrounding the atomic nuclei and the valence basins that are shared by the valence electrons deriving from several atoms. Figure 2 gives as an example in such an empty-core view of the electron distribution in a portion of space occupied by the (ZnCl 2 ) 3 trimer in its twisted-chain ground-state geometry and by the (HgBr 2 ) 3 trimer in its stair-like geometry.…”

Competitive coordination between lead and oligoelements with respect to some therapeutic heavy‐metal chelators

“…The third one is d-penicillamine (␤-thiovaline), which has been designed more recently [20,21]. From this quantum chemistry investigation, which is in line with a systematic work initiated in our group since a few years and dedicated to an in-depth understanding of the Pb 2ϩ cation chemistry [22][23][24][25][26], it is expected that some among the critical chemical parameters governing the chelation selectivity toward Pb 2ϩ can be drawn out and help in designing more selective chelating agents.…”

Enforcing hemidirectionality in Pb(II) complexes: The importance of anionic ligands

“…The aim of this theoretical work is to focus on some characteristics that a chelator must have to be selective. Such an achievement requires a better understanding of the Pb 2+ valence lone pair behavior in various environments since it has been shown in several quantum chemistry studies to be the driving entity governing the chemical physics of lead at a molecular level [10][11][12][13][14][15][16][17]. Indeed, it is well-known that this lone pair can be hemidirected (extending into one hemisphere and being stereochemically active), holodirected (surrounding the Pb 2+ cation and being stereochemically inactive), or even bisdirected (stereochemically active but split into two opposite lobes) [13], as depicted in Figure 1.…”

“…We chose Cl À /HCl in order to have a representative electronegative ligand and SH À /SH 2 as a model of a softer ligand. Following our previous studies, we have resorted to the topological analysis of the Electron Localization Function (ELF) [18,19] to characterize the directionality of the valence lone pair [10][11][12][13][14][15][16][17].…”