Self-assembly of functional macrocyclic metal complexes and 4-(phenylazo)benzoic acid: preparation, structure, and photoluminescence

Two self-assembled compounds [Ni(C18H42N6)(C13H9N2O2)2]·2CH3CN (3) and [Cu(C18H42N6)(H2O)2](C13H9N2O2)2 (4) were obtained by the reaction of 4-(phenylazo)benzoate (pab−) with macrocyclic complexes [Ni(C18H42N6)](ClO4)2 (1) and [Cu(C18H42N6)](ClO4)2 (2), respectively (C18H42N6 = 1,8-dipentyl-1,3,6,8,10,13-hexaazacyclotetradecane, C13H9N2O2 = 4-(phenylazo)benzoate). Compounds 1–4 were characterized by elemental analysis, IR, UV–Vis, photoluminescence and single crystal X-ray diffraction. The nickel(II) ion in 1 has a square planar geometry by coordination with four nitrogens of a macrocyclic ligand with pentyl groups, while the copper(II) ion in 2 has a distorted octahedral geometry by coordination with four nitrogen atoms in a square planar configuration and two oxygens of two perchlorate ions. In 3, the nickel(II) macrocyclic unit binds two pab− ions in axial position. The coordinated pab− ions are involved in hydrogen bonds with adjacent pab− ions, which gives rise to a 1-D ribbonlike structure. The copper(II) ion in 4 coordinates two water molecules axially. In 4, pab− ions as anions in the solid state are involved in hydrogen bonding interactions with coordinated water molecules and offset face-to-face π–π interactions between the benzene rings of pab− ions, which leads to a 2-D sheet structure. Potassium 4-(phenylazo)benzoate and 4 show strong fluorescence bands at 402 and 467 nm, and 397 and 467 nm, respectively. However, no fluorescence bands in 3 are observed due to the coordination of pab− ion to nickel(II) ion.