Crystal structure and magnetic properties of the flexible self-assembled two-dimensional square network complex [Cu2(mal)2(H2O)2(4,4′-bpy)] (H2mal=malonic acid and 4,4′-bpy=4,4′-bipyridine)

The copper(II) complex [Cu2(mal)2(H2O)2(4,4′-bpy)] (1) (H2mal=malonic acid and 4,4′-bpy=4,4′-bipyridine) has been prepared and its structure determined by single crystal X-diffraction methods. Compound 1 has a two-dimensional square grid network structure. The square grids are stacked parallel but in a staggered manner on each other along the c-axis, with an interlayer separation of 3.850(1) Å. Each layer contains a large cavity of 15.784(1)×15.784(1) Å with each edge shared by one malonate group and one 4,4′-bpy ligand and a small planar square of 4.644(1)×4.644(1) Å with Cu(II) ions and malonate groups at each corner and side, respectively. Each copper atom is in a distorted square-pyramidal surrounding with three carboxylate-oxygen atoms from two malonate groups and one nitrogen atom from a 4,4′-bpy ligand building the equatorial plane and a water molecule in the axial position. Each 4,4′-bpy molecule exhibits the bis-monodentate bridging mode whereas the malonate simultaneously adopts the bidentate (at one copper atom) and monodentate (at the adjacent copper atom) coordination modes. The bridging carboxylato exhibits the anti–syn coordination mode. The magnetic properties of 1 have been investigated in the temperature range 1.9–300 K and they correspond to a dominant ferromagnetic coupling through bridging malonato within the small square defined by four copper(II) ions (J=+12.4(1) cm−1) and much weaker intrasheet antiferromagnetic coupling between copper(II) ions through bridging 4,4′-bpy (jeff=−0.052(1) cm−1).