Adduct formation between U(TTA)4 and neutral donors triphenyl phosphine oxide (TPPO), tri-n-butyl phosphate (TBP) and methyl-isobutyl ketone (MIBK) in benzene was studied by absorption spectra. All the three donors form 1∶1 adduct with U(TTA)4. The adduct formation constants calculated from the spectral changes were 5·2×104, 1·1×103 and ∼0·8 for the adducts with TPPO, TBP and MIBK respectively. The adduct formation apparently increases the coordination number of U(IV) from 8, in the U(TTA)4 to 9 in the adduct formed.
