Metal-Complexes of Thiocholinate, -SCH₂CH₂Nme₃⁺. I. Preparation and Crystal-Structure of Pentakis(Thiocholinato)Dilead(II) Hexafluorophosphate

Abstract

Aqueous solutions containing lead(II) and deprotonated thiocholine contain water-soluble homoleptic lead thiolates , which crystallize as yellow needles of [Pb₂(SCH₂CH₂NMe₃)₅] (PF₆)₄ in the presence of PF₆^-, but crystallize [ Pb (SCH₂CH₂NMe₃)₂](ClO₄)₂ with 1 : 2 stoichiometry in the presence of ClO₄^-. Crystalline [Pb²(SCH₂CH₂NMe₃)₅](PF₆)₄ contains almost linear chains composed of end-linked {(SR)₂Pb(μ-SR) Pb (SR)₂} coordination units, within which the primary Pb -S coordination (mean 2.73 Ǻ, sample e.s.d . 0.10 Ǻ) is orthogonal trigonal (S- Pb -S, mean 88.9°, sample e.s.d .3.7°) at each lead atom. Within the {Pb₂(SR)₅} unit there is one double bridge with two rimary bonds, and one double bridge involving one secondary Pb --S connection (mean 3.23 Ǻ, sample e.s.d . 0.12 Ǻ). Three double-bridges involving secondary Pb --S coordination link the ends of the dimetallic units, and consequently bis - and tris -double thiolate bridges alternate along the chain. Overall coordination at each lead atom is pseudo-octahedral, with one non-bonding electron pair and two cis secondary Pb --S bonds. The cationic tails of the ligands radiate from the chains into a matrix of PF₆^- ions, and the chains are approximately hexagonally close-packed with a separation of 14.4 Ǻ. Along the b axis there are homogeneous stacks of the ammonium functions, the anions, and the Pb, S chains, with a pseudo-symmetric repeat of b/3 in each stack, allowing disorder due to stacking faults. This disorder has been adequately modelled in the refinement, which also incorporated back-Fourier-transform techniques to avoid inaccuracies due to spherically disordered PF₆^- ions. Crystal data: Cc, 25.535(8), b 43.13(1), c 15.123(5)Ǻ, β 100.36(9)°, Z 12 (× Pb₂S₅C₂₅H₆₅N₅P₄F₂₄), 3585 observed data, R 0.066.