The nature of lead–sulfur interaction in [PbII(S2COEt)n]2−n (n = 1,2,3,4) complexes: topological exploration and formation analysis

Abstract

The electronic structure and the nature of Pb–S interaction in the [Pb^II(S₂COEt)_n]²⁻ⁿ (n = 1,2,3,4) complexes are investigated theoretically. The ELF analysis has been performed for qualitative assignment of position, shape and directionality of the valence basin V(Pb) of lead in these chelates. The Pb–S interaction is explored in the light of AIM formalism and NBO analysis. In all these complexes, lead mainly uses its 6p sub-shell to coordinate with the 3p sub-shells of S-atoms. In the [Pb(S₂COEt)₂] (n = 2) and [Pb(S₂COEt)₃]⁻ (n = 3) complexes, significant participation of 6d and 7s orbitals of lead is also observed. As lead mainly uses the 6p orbitals in coordinating with the sulfur atoms of xanthate ligands, the structure becomes more holodirected when the three components of the 6p sub-shell of lead become equally populated. The ELF analysis reveals that the stereochemical activity of the valence lone pair of lead decreases as n increases, leading the lead xanthate structures from hemi to holodirected. The energetics of these chelates in the gas phase show that [Pb(S₂COEt)₃]⁻ (n = 3) is the most stable one while [Pb(S₂COEt)]⁺ (n = 1) is the least, when formation of these complexes are considered from Pb²⁺ and (S₂COEt)⁻ ligands. The complexation of these chelates is also investigated in water using the continuum SMD model which shows that Pb(S₂COEt)₂ is the most stable and the stability decreases successively as n changes from 2 to 4. Thus the reason behind the formation of Pb(S₂COEt)₂ in froth floatation is revealed.