Lewis-base adducts of lead(II) complexes. Part 6. X-Ray structural characterisation of adducts of lead(II) bis(perchlorate) with dimethyl sulfoxide

Abstract

Crystallisation of lead(II) perchlorate from aqueous ethanolic solution containing various amounts of dimethyl sulfoxide (dmso) has resulted in the isolation of three distinct solvates of Pb^II: dmso stoichiometry 1:3, 1:5 and (probably) 1:6. Varying degrees of structural authentication have been provided for these materials. The 1:3 compound forms monoclinic crystals, space group P2₁/c, a= 15.722(7), b= 17.18(1), c= 15.032(5)Å, β= 101.78(3)°, Z= 4 dimers; the structure was refined to a residual of 0.055 for 3526 independent, ‘observed’ reflections. The compound is novel, comprising two distinctly different isomeric, centrosymmetric dimers, one half of each comprising the asymmetric unit. In dimer 1, the two lead atoms are bridged by a pair of O,O′-perchlorate groups [Pb–O 2.78(2) and 2.79(2)Å]; the remainder of the lead co-ordination sphere is made up of three dmso and one perchlorate ligand, all unidentate [Pb–O(dmso) 2.30(2)–2.37(1)Å, Pb–O(ClO₄) 3.04(3)Å]. In dimer 2, a compact PbO₂Pb central ring is found with bridging O-dmso ligands [Pb–O 2.42(1) and 2.79(1)Å]; the remainder of the lead co-ordination sphere consists of a pair of unidentate dmso ligands [Pb–O 2.31(1) and 2.25(1)Å] and a pair of bidentate perchlorate ligands [Pb–O 2.81(1)–3.12(2)Å]. A similar single crystal X-ray structural characterisation of the 1:5 compound shows the cell to be triclinic, space group P, a= 11.572(2), b= 11.344(3), c= 11.276(6)Å, α= 91.74(3), β= 102.71(3), γ= 90.48(2)°, Z= 2. The structure was refined to a residual of 0.050 for 4217 independent ‘observed’ reflections. The lead(II) environment comprises five unidentate O-dimethyl sulfoxide ligands and a symmetrically-co-ordinated bidentate perchlorate ligand, the latter equatorial in a quasi-pentagonal-bipyramidal array: Pb–O(dmso, axial) 2.531(7) and 2.433(7); Pb–O(dmso, equatorial) 2.348(7), 2.406(7) and 2.516(7); and Pb–O(ClO₄) 3.08(2) and 3.21(2)Å. For crystals of the material analysing as a 1:6 adduct, the symmetry is trigonal-hexagonal, with a= 20.479(3) and c= 6.777(8)Å. From cell-volume comparisons with the 1:3 and 1:5 phases, it would seem reasonable that this (at present) unresolved phase is a 1:6 complex.