STRUCTURE OF THE LEAD PICRATE COMPLEXES WITH 18-MEMBERED CROWN ETHERS IN THE CRYSTAL STATE AND IN ORGANIC SOLVENTS. N. K. Dalley¹, J. D. Lamb¹, A. Y. Nazarenko², E. B. Rusanov^{3, 1}Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, USA, ²Analytical Chemistry Department, Taras Shevchenko University, Kiev 252033, Ukraine, ³Institute of Organic Chemistry, NAS of Ukraine, Kiev, Ukraine

Despite the wide use of metal picrates for ion recognition studies, no structural data concerning lead picrate complexes with crown ethers have yet been published. Here we report molecular structures of Pb(18-crown-6)Picr₂ x CH₂Cl₂ (I) and Pb(cis-syn-cis-dicyclohexano-18-crown-6)Picr₂ (II). In both complexes Pb²⁺ is coordinated six O atoms of macrocycle, which has a distorted D_3d geometry (Pb...O separations are 2.64-2.84 Å). Both picrate anions in (I) and only one in (II) are monodentate with Pb...O = 2.47-2.48 Å, while the second one in (II) is bidentate (Pb...O = 2.56 and 2.88 Å). This correlates with the existence of different types of picrate - Pb²⁺ ion pairs in organic solvents in the presence of crown ethers, observed from spectral studies. The structural data together with our previously obtained structures of lead macrocyclic complexes enable us to discuss the features of ion recognition of Pb²⁺ by crown ethers.