Study of complexes of f-block elements-hydroxypyridinone systems: Pt. 1

The solution chemistry of Th(IV) with several hydroxypyridinones, 1-hydroxy-2 (1H) -pyridinone (1,2-HOPO) and 3-hydroxy-2 (1H) -pyridinone (3,2-HOPO) has been studied using potentiometric and spectrophotometric methods. The potentiometric measurements are described for the solution containing different ratios of hydroxypyridinones to Th(IV) in 0.10 mol/l KNO3 solution at 25 deg C. Several complexes of Th(IV) and hydroxypyridinones are formed in the solutions at different systems and pH values. The complexes of Th(1,2-OPO)3+,Th(1,2-OPO)22+,Th(1,2-OPO)3+ and Th(1,2-OPO)4 are formed at pH3.4, 4.0, 4.7, and 5.8, respectively. It is found that similar complexes are also formed for the system of 3, 2-HOPO and Th(IV), but the buffer region of metal complexation for 1,2-HOPO is lower in pH. The formation constants of the complexes are calculated using a non-linear least wquare program to refine potentiometric titration data by CDC CYBER 170/825 computer. It is found that the formation constants are as follows: logβ110=9.3(1), logβ120=17.2(4), logβ130=23.4(5) and logβ140=29.0(1) for Th(IV)-1,2-HOPO system and logβ110=10.4(2), logβ120=19.2(2), logβ130=26.6(6) and logβ140=32.4 for Th(IV)-3,2-HOPO system. The pM values of 1,2-HOPO and 3,2-HOPO for Th(IV) are 14.1(2) and 12.5(8) at pH 7.4, [M]T=1μmol/l and [L]T=10μmol/l respectively. These results are to be used in the design and refinement of actinide-specific macro-chelate sequestering agents