Structures of six photochromic 3d complexes containing 3,3′-azobis-1,2,4-triazole ligand

Six 3,3'-azobis-1,2,4-triazole (H(2)ABT) complexes [Mn-2 (ABT)(bpy)(4)(H2O)(2)]center dot(ABT)center dot 4H(2)O (1), [Mn(ABT)(H2O)(4)]center dot H2O (2), [Co(ABT)(en)(2)]center dot(H(2)ABT)center dot 2H(2)O (3), [Cd(ABT)(0.5)(en)(2)]center dot(ABT)(0.5)center dot 2H(2)O (4), [Zn(ABT)(0.5)(en)(2)]center dot(ABT)(0.5)center dot 2H(2)O (5), [Cu(ABT)(0.5)(en)(2)]center dot(ABT)(0.5) (6), where en = ethylenediamine, bpy = 2,2-bipyridine, have been synthesized and characterized by single crystal X-ray diffraction analysis. In complexes 1-6, the unusual face-to-face pi-pi stacking interactions among heterocyclic aromatic rings and three kinds of hydrogen bonds C-H center dot center dot center dot O, N-H center dot center dot center dot O and O-H center dot center dot center dot O are observed. The pi-pi stacking, hydrogen bonding and electrostatic interactions are responsible for the stabilization of these 2D and 3D supramolecular structures. The aqueous solutions of 1-6 with the concentration of 6 x 10(-5) mol dm(-3) show photochromism. The fluorescent properties of solid-state samples of 1-6 have been investigated. The pi-pi stacking interaction energies for 1-6 were calculated at MP2 level using Gaussian 09 suite and demonstrated.