Synthesis of a para-tert-octylcalix[4]arene fitted with phosphinoyl pendant arms and its complexation properties towards f-elements

A new functionalised calixarene, para-tert-octylcalix[4]arene, fitted with phosphinoyl pendant arms (B4boctL4) 1, was synthesised and fully characterised. The procedure using xylene via a Williamson reaction between the tetra sodium derivative of the calixarene and dimethyl-chloromethyl-phosphine oxide decreased the reaction time from 96 to 15 h and increased the reaction yield from 46% to 89% with respect to a reported procedure using toluene for the synthesis of a phosphinoylated calixarene with para-tert-butyl substituents. Spectrophotometric titrations of B4boctL4 with La(III), Lu(III), Th(IV) and UO22+ and luminescence titrations of Tb(III) and UO22+ were performed in CH3CN in the presence of 0.01 M (CH3CH2)4NCl. The results suggest the formation of two predominant species with 1:1 and 1:2 metal:ligand ratios. The former had a log β11 values of 8.4 and 4.5 for La(III) and UO22+ ions, respectively, and the latter had a log β12 values of 13.8 and 7.4, respectively. Based on this result, a 1 M:2 L molar ratio was used with the aim of isolating Eu(III) and UO22+ complexes with 1 M:2 L stoichiometry. However, the characterisation of the complexes indicated 1 M:1 L stoichiometry. The luminescence properties, such as emission and excitation spectra, lifetimes and quantum yields, of the UO22+ (2) and Eu(III) (3) isolated complexes were analysed. The molecular modelling of the europium complex molecule based on the experimental results suggested a coordination number equal to 9 and a distorted tri-capped trigonal prismatic geometry as the most probable structure. The extraction ability of the titled calixarene in CHCl3 towards UO22+, Th(IV), La(III) and Eu(III) ions from 1 M HNO3/3.5 M NaNO3 aqueous medium was investigated. Tributylphosphate (TBP) (2.4 × 10−4 M) added to the calixarene ligand (2.4 × 10−4 M) (v/v) both in CHCl3 caused a significant synergistic effect on the uranyl extraction, increasing the extraction from 48% to 96%. Under our conditions, TBP in CHCl3 extracted only 11%. The capability and loading capacity of B4boctL4 towards Th (IV) ions were studied.

Para-tert-octylcalix[4]arene fitted with phosphinoyl pendant arms (B4boctL4) was synthesised, characterised and modelled. Spectrophotometric titrations of B4boctL4 with actinides and lanthanides, and luminescence titrations of UO22+, which were performed in CH3CN in the presence of 0.01 M (CH3CH2)4NCl, indicated the formation of two predominant species with 1:1 and 1:2 metal:ligand ratios. Europium and uranyl complexes were obtained in 1 M:1 L stoichiometry and their photophysical properties were studied. The extraction ability of B4boctL4 in CHCl3 towards actinides and lanthanides from acidic-salty aqueous medium was investigated. A significant synergistic effect on the uranyl extraction of tributylphosphate added to B4boctL4 both in CHCl3 was observed. The capability and loading capacity of B4boctL4 towards Th (IV) ions were analysed.Figure optionsDownload as PowerPoint slide