Two Zn(II) and Cd(II) compounds derived from 9-aminoacridine: Syntheses, characterizations, crystal structures and solution Studies

The aqueous reactions of zinc(II) and cadmium(II) nitrate and pyridine-2,6-dicarboxylic acid, (pydcH 2 ), with 9-aminoacridine, (AAcr), resulted in the formation of two new proton transfer compounds, (AAcrH) 2 [Zn(pydc) 2 ].3H 2 O ( 1 ) and (AAcrH) 2 [Cd(pydc) 2 ].4H 2 O ( 2 ). The compounds were characterized using IR spectroscopy and single crystal X-ray diffraction. Both compounds crystallized in the triclinic crystal system, space group P1̅ , with two molecules per unit cell. The anions were six-coordinate complexes with distorted octahedral geometries around the Zn(II) and Cd(II) centers. The dihedral angles indicated that the two (pydc) 2− ligands were almost perpendicular to each other. The complex anions of [M(pydc) 2 ] 2- were neutralized with (AAcrH) + cations. These cations formed extended stacks throughout the structures. The water molecules clustered around cyclic tetramers, bridging the anions and forming a link to the aminoacridiunium stacks. A potentiometric pH titration method was used to investigate the protonation constants of AAcr and pydc, the pydc-AAcr proton transfer equilibrium constants, and the stoichiometries and stabilities of complex formation with Zn 2+ and Cd 2+ ions in 50