The complexation abilities of 2,2'-bipyridine (bipy) and 2,2'-bipyridyl-N,N'-dioxide (bipydiox) toward zinc(II) and the influence of these ligands on the properties and reactivities of the investigated complexes are compared by means of mass spectrometry, IR multiphoton dissociation spectroscopy, and theoretical calculations. The binding energy of bipydiox to zinc is slightly smaller than that of bipy, namely, by 0.1 eV in the mixed complex [(bipy)(bipydiox)ZnCl](+). Accordingly, the differences in the properties and reactivities of the complexes of zinc(II)/bipydiox and zinc(II)/bipy are only minor. The mechanism of decarboxylation of [(L)Zn(CH3COO)](+) (L = bipy or bipydiox) is investigated in detail. The substantial difference between the ligands stems only from the possibility of oxygen transfer from bipydiox, which is here, however, observed only as a high-energy channel in the fragmentation of complexes [(bipydiox)Zn(CH3COO)](+).