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

Abstract

Six 3,3′-azobis-1,2,4-triazole (H₂ABT) complexes [Mn₂ (ABT)(bpy)₄(H₂O)₂]·(ABT)·4H₂O (1), [Mn(ABT)(H₂O)₄]·H₂O (2), [Co(ABT)(en)₂]·(H₂ABT)·2H₂O (3), [Cd(ABT)_0.5(en)₂]·(ABT)_0.5·2H₂O (4), [Zn(ABT)_0.5(en)₂]·(ABT)_0.5·2H₂O (5), [Cu(ABT)_0.5(en)₂]·(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 π–π stacking interactions among heterocyclic aromatic rings and three kinds of hydrogen bonds C–H⋯O, N–H⋯O and O–H⋯O are observed. The π–π 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 × 10⁻⁵ mol dm⁻³ show photochromism. The fluorescent properties of solid-state samples of 1–6 have been investigated. The π–π stacking interaction energies for 1–6 were calculated at MP2 level using Gaussian 09 suite and demonstrated.