Synthesis, characterization, spectroscopic, crystal structures and solution studies of two coordination compounds of zinc(II) and iron(III) based on chelidamic acid and acridine

Two new proton transfer compounds, (acrH)(2)[Zn(hypydc)(2)]center dot 10H(2)O 1 and (acrH)[Fe(hypydc)(2)]center dot 4.5H(2)O 2 [where hypydcH(2) = 4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid) and acr = acridine] have been synthesized and characterized by elemental analysis, spectral (UV-Vis, IR), H-1 NMR, C-13 NMR spectroscopy and single crystal X-ray diffraction. The crystallographic analysis revealed that Zn-II and Fe-III atoms are coordinated by two N atoms and four O atoms from the carboxylate groups of (hypydc)(2) ligands, forming a distorted octahedral geometry. In the anions two pyridine rings are inclined to one another by 88.10(5)degrees and 83.95(13)degrees for 1 and 2, respectively. The (H2O)(n) [n = 3-6] cyclic-linear water clusters connected two layers of anionic complexes in 1. The crystal packing of 1 show a 3D network formed through H-bonds involving water molecules, NH groups of acridinium and carboxylate anions. In 2 two types of rubout O-H center dot center dot center dot O hydrogen bond synthons, R-4(4) (16) and R-4(4) (18) link the anions and water molecules to form two-dimensional network parallel to bc plane. In crystal structures of both complexes extensive O-H center dot center dot center dot O, N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds as well as electrostatic forces, C-O center dot center dot center dot pi and pi-pi stacking play important roles in stabilizing structures. The protonation constants of hypydc and acr, in all of probability protonated forms, the equilibrium constants for the hypydc-acr proton transfer system and the stoichiometry and stability of complexation of this system with Zn2+ and Fe3+ ions in 50% dioxane-50% water (V/V) solvent were investigated by potentiometric pH titration method. The stoichiometries of the most complex species in solution were compared with corresponding crystalline metal ion complexes 1 and 2. (C) 2012 Elsevier B. V. All rights reserved.