Supramolecular influences on metal ion coordination: Lead(II) under eight-coordination

Crystal structure determinations on the "acid salt" of Pb(II) and dipicolinic acid (pyridine-2,6-dicarboxylic acid, dipicH(2)), regarded as composed of dimer entities, [Pb-2(dipic)(2)(dipicH(2))(2)(OH2)(6)], 1, infinitely cross-linked, and on the complex of 2,4-dinitrophenol (2,4-DNPH), a simpler coordination polymer, [Pb(2,4-DNP)(2)](n), 2, show both solid state structures to be influenced by pi-stacking of the ligands. Although the Pb(II) coordination environment in 1 can be regarded as "hemidirected" and that in 2 as "holodirected", it is argued that inter-dimer stacking interactions, rather than lone pair effects, are responsible for the distorted 9-coordination of Pb in 1. In 2, Pb adopts close-to-cubic 8-coordination.