NMR spectroscopic study of adduct formation of neptunium(IV) β-diketonates

Neptunium(IV) pivaloyltrifluoroacetonate Np(PTFA)4, its adduct with trimethylphosphine oxide (TMPO), neptunium(IV) hexafluoroacetylacetonate Np(HFA)4, and its adducts with TMPO and trimethyl phosphate (TMP) were synthesized. It was shown by NMR spectroscopy that adducts of Np(PTFA)4 with TMPO and Np(HFA)4 with TMP have a 1:1 composition; moreover, there is no coordination of subsequent molecules of the neutral ligand when it is present in excess. In the system Np(HFA)4=TMPO, on the contrary, the formation of 1:1, 1:2, and 1:3 adducts is observed; moreover, in the last two cases there is an opening of the chelate rings with maintenance of a coordination number of 9 for neptunium. Thus, the ability of NP(IV) β-diketonates for adduct formation increases sharply as the basicity of the β-diketonates anion is weakened [the previously studied perfluorinated chelate - neptunium(IV)dipivaloylmethanate - does not form adducts at all]