Atomic absorption spectroscopy of the ionic liquid 1-ethyl-3-methylimidazolium ethanoate ([emim]2[O2CMe]), prepared according to International Patent WO 96/18459, showed it to contain large amounts of lead impurity: (ca. 0.5 M): [emim]2[Pb(O2CMe)4] was isolated and shown crystallographically to contain the first known example of a monomeric, homoleptic pentacoordinate lead(II) carboxylate complex, with a stereochemically active lone-pair.
