Structural characterization of a Pd₃(bitmb)₄Cl₆·Pd₂(bitmb)₄Cl₄·18H₂O·2CH₃OH (1) (bitmb = 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene) complex shows that it is a unique example of a co-crystal that includes both a M₃L₄ metallocage, Pd₃(bitmb)₄Cl₆, and a M₂L₄ metallocage, Pd₂(bitmb)₄Cl₄, in a 1 : 1 ratio. Single crystal analysis indicates that the structures of M₃L₄ and M₂L₄ in co-crystal 1 are almost identical to those of the free metallocages. However, both the M₃L₄ and M₂L₄ metallocages are flexible and their sizes and shapes can be mediated in co-crystal 1 by strong π⋯π interactions between the M₃L₄ and M₂L₄ metallocages, CH⋯Cl H-bonds between the M₃L₄ metallocages and so on. Such a packing mode may govern the formation of the M₂L₄ and M₃L₄ co-crystal complex in a 1 : 1 ratio. Furthermore, the combined reaction procedures allow the formation of 1 + 1 M₂L₄ and M₃L₄ co-crystal complex 1 in the solid state.