Lanthanoid Coordination with a Tetrazole-Substituted Calix[4]diquinone and Calix[4]dihydroquinone

The tetrazole-functionalised calixdiquinone 5,17-di-tert-butyl-26,28-bis-(tetrazol-5-ylmethoxy)- calix[4]-25,27-diquinone Q was synthesised by chemical oxidation of the bis-tetrazole calix[4]arene precursor using PbO2/HClO4. The single crystal X-ray structure determination of Q confirmed the structure and showed binding of a water molecule in the solid state. Chemical reduction of Q to the dihydroquinone QR was achieved using N,N-diethylhydroxylamine. Comparison of the solution phase photophysical properties of Q or QR in the presence of terbium ions showed significant excitation only with QR, suggesting redox switching of the photophysical response may be possible with this or similar receptors.