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

摘要

Two new proton transfer compounds, (acrH) _2[Zn(hypydc) _2]·10H _2O 1 and (acrH)[Fe(hypydc) _2]·4.5H _2O 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), 1H NMR, 13C 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)° and 83.95(13)° for 1 and 2, respectively. The (H _2O) _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?O hydrogen bond synthons, R44 (16) and R44 (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?O, N-H?O and C-H?O hydrogen bonds as well as electrostatic forces, C-O?π and π-π 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 Zn ~(2+) and Fe ~(3+) 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.