Complexation of the [99Tc(CO)3(H2O)3]+ Ion with Phosphoric Acid Anions in Aqueous Solution: A 99Тс NMR Study

The complexation of the [99Tc(CO)3(H2O)3]+ ion with phosphoric acid anions in aqueous solution was studied by 99Тс NMR. In acid solutions, 1 : 1, 1 : 2, and 1 : 3 complexes with the H2PO4– anion are formed; their stepwise stability constants are 1.0 ± 0.2, 0.20 ± 0.03, and 0.07 ± 0.03 L/mol, respectively. The complexation with the HPO42– anion at pH 6–7 is complicated by the hydrolysis of the triaqua complex to form the stable tetramer [99Tc(OH)(CO)3]4. The stability constant of the 1 : 1 complex with the HPO42– ion is estimated at 102 L/mol. Higher-field signals assignable to the 1 : 2 and 1 : 3 complexes with the HPO42– and H2PO4– anions are also observed.