Actinide complexes of the calixarenes. Part 1. Syntheses and crystal structures of bis(homo-oxa)-p-tert-butylcalix[4]arene and its uranyl ion complex
Abstract
Interaction of the uranyl ion with the potentially quinquedentate calixarene bis(homo-oxa)-p-tert-butylcalix[4]arene, C45H58O5(H4L), in the presence of amine bases results in the formation of the red-brown, anionic complex [UO2(L)]2–. Crystal-structure determinations of the hydrated triethylammonium salt of this complex [monoclinic, space group C2/c(C2h6, no. 15), a= 29.81(2), b= 16.653(7), c= 26.38(2)Å, β= 115.47(4)°, Z= 8, R= 0.049 for 6608 ‘observed’ reflections] and of the dimethylformamide adduct of the free ligand [monolinic, space group P21/m(C2h2, no. 11), a= 9.701(1), b= 25.108(9), c= 9.230(3)Å, β= 95.97(2)°, Z= 2, R= 0.067 for 1749 ‘observed’ reflections] show that the ligand adopts a very similar ‘cone’ conformation in both instances, and that the uranium–ligand interaction is primarily through the four phenoxide donor atoms, with only a remote (and presumably weak) contact between the uranium and ether-oxygen atoms. One of the triethylammonium counter cations is included within the cone of the co-ordinated ligand in a very similar way to the inclusion of dimethylformamide by the free ligand, and 1H NMR spectroscopy indicates that this inclusion persists in solution. Uranyl ion luminescence is quenched completely in solutions of the complex at room temperature.