FT-IR Characterization of Metal Acetates in Aqueous Solution

A correlation has been developed between antisymmetric and symmetric carboxylate group infrared absorption frequencies, cationic radii, and acetate group types that can be used to differentiate between ionic, unidentate, bidentate, and bridging acetate groups in aqueous metal acetate solutions. In solutions containing the alkali metal, alkaline earth, and Mn(II), Co(II), and Ni(II) ions, the acetate group is primarily ionic. The bound acetate groups in Ce(III), Pb(II), Sm(III), Y(III), and Yb(III) systems are bidentate. A solution of Cr(III) acetate has bridging acetate groups. Cu(II), Zn(II), and Cd(II) appear to form H-bonded unidentate structures in which an acetate oxygen not coordinated to the metal is hydrogen bonded to a coordinated water molecule. Hg(II) acetate has bridging acetate groups and might also have unidentate acetate groups.