Robust anionic building blocks [M(malonate)2(H2O)2]2− for crystal engineering of inorganic–organic hybrid materials

One-pot reactions of transition metal (CuII, NiII, CoII, or CdII) salt with malonic acid (H2mal) in the presence of mesocyclic diamine generate three supramolecular complexes and a coordination polymer. [Cu(mal)2(H2O)2](H2O)2(H2DACH) (1) and [M(mal)2(H2O)2](H2DACO) (M = Ni for 2, and Co for 3) are ion-pair products and managed by charge-assistant noncovalent interactions (DACO = 1,5-diazacyclooctane, and DACH = 1,4-diazacycloheptane). In these structures, the similar mononuclear [M(mal)2(H2O)2]2− building blocks are connected by hydrogen bonds to form 2D networks (with the aid of one lattice water in the case of 1), which are further extended by the cationic diamine components to yield 3D pillar-layered solids. While [Cd(mal)(H2O)2]n (4) is a neutral polymeric complex, in which the similar [Cd(mal)2(H2O)2]2− subunits are propagated by additional Cd–O coordinative forces to result in the final 2D layer.