Ultraviolet spectroscopic evidence for polynuclear lead (II) complexes in synthetic Red Sea brines

The Pb complexes in a synthetic brine solution with a composition comparable to that of the Atlantis II Deep 56°C Brine have been identified by UV absorption spectroscopy. The important species at ambient temperatures are PbCl^2?₄ and Pb(OH)BrCl₂^2?. At 56°C the former complex partially dissociates to form lower chloro complexes while the latter undergoes halide exchange reactions forming Pb(OH)Br₂Cl^2?. Evidence has also been found for the following polymeric lead hydroxo complexes: Pb₄(OH)₄Cl₄, Pb₆(OH)₃Cl₁₂ and Pb₃(OH)₁₂Cl₄. The predominant polynuclear complex in the brine, Pb₄(OH)₄Cl₄, tends to dissociate at 56°C to form lower polymeric species. The formulation of the limiting binary chloro complex as PbCl₄^2? rather than PbCl₆^4? is supported by the reflectance spectrum of Cs₄PbCl₆.