INTERACTIONS IN AQUEOUS-SOLUTION AT 25-DEGREES-C OF PALLADIUM(II) AND MERCURY(II) WITH 1,4-DITHIA-18-CROWN-6 AND 1,10-DITHIA-18-CROWN-6 - A THERMODYNAMIC, SPECTRAL, AND X-RAY CRYSTALLOGRAPHIC STUDY

Log K, ΔH, and ΔS values for the interactions of Hg(II) and Pd(II) with l,4-dithia-18-crown-6 (1,4-T218C6) and 1,10-dithia-18-crown-6 (1,10-T218C6) were determined in aqueous solution at 25 °C by polarography and competitive calorimetry. The reaction stoichiometries of either metal ion with 1,4-T218C6 and 1,10-T218C6 are 1:2 and 1:1, respectively. The formation of both metal complexes of 1,10-T218C6 is favored by both °H and °S, while that of both metal complexes of 1,4-T218C6 is favored by °H only. The thermodynamic results have been interpreted in terms of ligand field stabilization energy (LFSE), charge-transfer, and macrocyclic effects. The UV/vis absorption spectra of Pd(Il) complexes with both crown thioethers in 0.5 M HN03show that LFSE and charge-transfer effects make large contributions to the formation of the very stable complex Pd(l,4-T218C6)22+. The molecular structures of Pd(II) complexes with both crown thioethers have been determined by single-crystal X-ray analysis. The complex Pd(l,10-T218C6)(NO3)2crystallizes in the orthorhombic Pna2, space group with ± = 10.508 (4) Å, b = 13.871 (7) Å, c = 13.772 (7) Å, Z = 4, and R = 0.064. The complex Pd(l,4-T218C6)2(N03)2crystallizes in the orthorhombic Pbca space group with a = 8.474 (2) Å, b = 18.349 (5) Å, c = 148.969 (25) Å, Z = 8, and R = 0.083. A cis-square-planar configuration is found for the Pd(l,10-T218C6)2+complex. © 1990, American Chemical Society. All rights reserved.