Azocalixarenes. 6: Synthesis, complexation, extraction and thermal behaviour of four new azocalix[4]arenes

Four new azocalix4]arenes {5,11,17,23-tetrakis(2-hydroxy-5-tert-butylphenylazo)]-25,26,27,28-tetrahydroxycalix4]arene (1), 5,11,17,23-tetrakis(2-hydroxy-5-nitro phenylazo)]-25,26,27,28-tetrahydroxycalix4]arene (2), 5,11,17,23-tetrakis(2-amino-5-carboxylphenylazo)]-25,26,27,28-tetrahydroxycalix4]arene (3) and 5,11,17,23-tetrakis(1-amino-2-hydroxy-4-sulfonicacidnapthylazo)]-25,26,27,28-tetrahydroxycalix4]arene (4)} have been synthesized from p-tert-butylphenol, p-nitrophenol, p-aminobenzoic acid and 1-amino-2-hydroxy-4-sulphonic acid by diazo coupling reaction with p-aminocalix4]arene. The resulting ligands (1–4) were treated with three transition metal salts (e.g., CuCl₂·2H₂O, NiCl₂·6H₂O or CoCl₂·6H₂O). Cu(II), Ni(II) and Co(II) complexes of the azocalix4]arene derivatives were obtained and characterized by UV-vis, IR, ¹H-NMR spectroscopic techniques and elemental analysis. All the complexes have a metal:ligand ratio of 2:1. The Cu(II) and Ni(II) complexes of azocalix4]arenes are square-planar, while the Co(II) complexes of azocalix4]arenes are octahedral with water molecules as axial ligands. The solvent extraction of various transition metal cations from the aqueous phase to the organic phase was carried out by using azocalix4]arenes (1–4). It was found that, azocalix4]arenes 1, 2 and 3 examined selectivity for transition metal cations such as Ag⁺, Hg⁺ and Hg²⁺. In addition, the thermal stability of metal:azocalix4]arene complexes were also reported. Dedicated to Prof. Dr. Mustafa Yılmaz on the occasion of his 50th birthday