1D and 3D supramolecular structures exhibiting weak ferromagnetism in three Cu(II) complexes based on malonato and di-alkyl-2,2’-bipyridines

<p>Three new Cu(II) complexes composed of malonato (mal), methylmalonato (memal), 4,4′-di-tert-butyl-2,2′-bipyridine (tbpy) and 5,5′-dimethyl-2,2′-bipyridine (mebpy) ligands, Cu(H<sub>2</sub>O)(mal)(tbpy) (<b>1</b>), Cu(H<sub>2</sub>O)(memal)(tbpy) (<b>2</b>) and Cu<sub>4</sub>(H<sub>2</sub>O)<sub>4</sub>(memal)<sub>4</sub>(mebpy)<sub>4</sub>·11H<sub>2</sub>O (<b>3</b>) were synthesized by simple one-pot solution reactions at ambient conditions. Single-crystal X-ray diffraction analyses reveal that the Cu(II) ions exhibit a distorted five-coordinate square pyramidal geometry. These three complexes display supramolecular arrays due to hydrogen-bonding interactions. Complexes <b>1</b> and <b>2</b> show 1-D supramolecular structures; <b>1</b> forms a double-ion chain, unlike <b>2</b>, which only generates a single-ion chain. In <b>3</b>, there are two identical monomers in the asymmetric unit with <i>Z″</i> = 2; its high number of noncoordinated water molecules, along with hydrogen-bonding interactions between aqua ligand and memal ligand, generate a supramolecular tetramer, which mimics to produce a 3-D supramolecular framework. Besides this fascinating and yet uncommon crystallographic phenomenon in <b>3</b>, the structural differences found in these complexes arise from the substituted groups in the malonato dianion and in the bipyridine ligands. These compounds exhibit weak ferromagnetic-exchange interactions.</p>