Crystal engineering of 3-D coordination polymers by pillaring ferromagnetic copper(ii)-methylmalonate layers

Abstract

Three new copper(II) complexes of formula [Cu(Memal)(H₂O)]_n (1), [Cu₂(pyz)(Memal)₂] (2) and [Cu₂(4,4′-bpy)(Memal)₂(H₂O)₂] (3) (Memal = methylmalonate, pyz = pyrazine and 4,4′-bpy = 4,4′-bipyridine) were obtained and structurally characterized by X-ray diffraction. Complex 1 is a square grid of aquacopper(II) units which are linked by carboxylate-methylmalonate groups in the anti–syn (equatorial–equatorial) coordination mode. The crystal structures of 2 and 3 consist of corrugated layers of copper(II) (2) and aquacopper(II) (3) units with intralayer carboxylate-methylmalonate bridges in the anti–syn (equatorial–apical) coordination mode which are linked through pyrazine (2) and 4,4′-bipyridine (3) ligands; to build up a 3-D network. Magnetic susceptibility measurements of complexes 1–3 in the temperature range 2–300 K show the occurrence of an overall ferromagnetic behaviour with a weak intralayer ferromagnetic coupling (J = +1.61(1) cm⁻¹) in 1 whereas two opposite magnetic interactions occur in 2 and 3, one ferromagnetic through the anti–syn carboxylate (2 and 3) and the other antiferromagnetic through pyz (2) and 4,4′-bpy) (3).