A Cu(II)-methylmalonate complex, (C 3 H 7 N 6 ) 4 [Cu(II)(C 4 H 4 O 4 ) 2 ](H 2 O) 4 Cl 2 ( 1 ) (where C 3 H 7 N 6 = protonated melamine, C 4 H 4 O 4 = methylmalonic acid), has been synthesized from aqueous media and its crystal structure was determined by single-crystal X-ray diffraction. The anionic Cu(II)-methylmalonate complex mediated formation of interesting supramolecular assemblies in the solid state by means of ionic interactions with protonated melamine. Moreover, other forces such as antielectrostatic H-bonding and π + – π + interactions also play a crucial role in defining the final 3-D architecture of 1 . An interesting stacking among protonated melamine molecules is studied by DFT calculations. Lattice water molecules and chlorides form various hydrogen bonds to take part in the self-assembly processes.