Structures of (oxodimethylenemethane)palladium and -platinum complexes in solution and in crystalline states were investigated by H-1 NMR, IR, and X-ray crystallographical analyses. The following features are disclosed: the structures consisted of contributions from pi-allylic and metallacyclobutanone canonical forms; the palladium complex has a larger contribution of pi-allylic character than the platinum complex in both states; the degree of contribution of pi-allylic character increased upon the increment of solvent polarity and the addition of protic solvent.