Synthesis, metal binding and spectral properties of novel bis-1,3-diketone calix[4]arenes

New bis-1,3-diketone derivatives of calix[4] arene (3-5) have been synthesized with good yields by the addition of a sodium salt of acetylacetone, 1-benzoylacetone and dibenzoylmethane to 5,17-bis-(bromomethyl)25,26,27,28- tetrahydroxycalix[4] arenes. The structural properties of the obtained compounds and their complexes have been established by means of IR, UV-Vis, NMR spectroscopy and quantum-chemical calculations. The complex ability of bis-1,3-diketones towards Al3+, Ni2+, Cu2+ and lanthanide ions (Nd3+, Eu3+, Tb3+) has been investigated by using a liquid-liquid extraction method. The UV-Vis data indicate thermodynamically favorable 1 : 1 complex formation of the ligands with Tb3+ in alkaline DMF, although the time required for the equilibration reveals the difference between calix[4] arenes bearing acetylaceton-, benzoylaceton-and dibenzoylmethane-substituents. The steric hindrance effect on ketoenol transformation is the reason for the difference. The ligand-centered emissions of Gd3+ complexes with benzoylaceton- and acetylaceton-substituted calix[4] arenes reveal them both as more convenient antennae for red and infra-red than for green lanthanide luminescence. Indeed, the benzoylaceton-substituted counterpart sensitizes Yb3+-centered luminescence to a good extent. Nevertheless, the luminescence of Tb3+ is sensitized by the acetylaceton-substituted counterpart to a better extent than that of Yb3+, while only poor red Eu3+ emission is observed under sensitization by both the ligands.