Hydrogencyanamido bridged multinuclear copper(ii) complexes: from strong antiferromagnetic couplings to weak ferromagnetic couplings

Abstract

In the presence of ammonia, the reactions of cyanamide and Cu^II ions with different organic blocking ligands afford three hydrogencyanamido bridged dinuclear complexes: [(dmbpy)₄Cu₂(HNCN)](ClO₄)₃·H₂O (1, dmbpy = 4,4′-dimethyl-2,2′-bipyridine), [(phen)₄Cu₂(HNCN)](ClO₄)₃·2H₂O (2, phen = 1,10-phenanthroline) and [(bpy)₂Cu₂(HNCN)₂(ClO₄)₂] (3, bpy = 2,2′-bipyridine), respectively. However, using the di(2-pyridyl)ketone (dpk) ligand in similar experimental conditions, an interesting reaction between the hydrogencyanamido anion and dpk is observed. Using Cu(ClO₄)·6H₂O or Co(ClO₄)·6H₂O as the metal source, it gives the mixed bridged hexanuclear complex [(dpk·OMe)₄(dpk·NCN)₂Cu₆(H₂O)₂](ClO₄)₄ (4), or the mononuclear complex [(dpk·OMe)(dpk·HNCN)Co](ClO₄)·2H₂O (5), respectively. Their structures are characterized by single crystal X-ray diffraction analyses. Magnetic measurements reveal moderate antiferromagnetic interaction between the Cu^II ions in complex 1, weak ferromagnetic coupling in complex 2, and strong antiferromagnetic interactions for complexes 3 and 4. The magnetostructural correlations of these complexes are discussed.