Carboxylate anions in aqueous solutions coordinate with the Tc(CO) ₃ ⁺ ion mainly in the monodentate fashion to form weak 1 : 1, 1 : 2, and 1 : 3 complexes. The stability of the complexes decreases with increasing size of the alkyl radical. In the series of halo-substituted acetates, all the stability constants decrease with a decrease in the basicity of the anion.