Lead-citrate chemistry. Synthesis, spectroscopic and structural studies ofa novel lead(II)-citrate aqueous complex

The interaction of lead with biologically relevant ligands, such as citrate , constitutes a major research thrust relating to toxic effects exerted on humans. Reaction of Pb(NO3)(2) with citric acid in water at pH 2 and variou s ratios (1:1-1:3) yielded the first Pb-citrate species, which was characte rized analytically and spectroscopically (FT-IR). X-ray crystallographic st udies were carried out and showed the novel compound to be [Pb(C6H6O7)](n). nH(2)O. The geometry around Pb2+ appears to be distorted trigonal bipyramid al with Pb-O distances ranging from 2.397(7) to 2.527(6) Angstrom and the l one pair on Pb2+ occupying one of the three basal plane positions. Citrate binds Pb2+ forming rhomboidal Pb2O2 units, while it subtends its terminal c arboxylate onto a proximal Pb2+, thus linking adjacent Pb2O2 units into a c hain along the a axis. The involvement of citrate in hydrogen bonds with wa ter molecules and abutting Pb-citrate moieties leads to a stable structure. The stability of the species formed and eventually isolated from aqueous s olutions as well as its reactivity toward bases present useful information on the chemistry in biological media and its relevance to the known biotoxi city of lead. (C) 2000 Elsevier Science S.A. All rights reserved.