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

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)(4)Cu(2)(HNCN)](ClO(4))(3)·H(2)O (1, dmbpy = 4,4'-dimethyl-2,2'-bipyridine), [(phen)(4)Cu(2)(HNCN)](ClO(4))(3)·2H(2)O (2, phen = 1,10-phenanthroline) and [(bpy)(2)Cu(2)(HNCN)(2)(ClO(4))(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(ClO(4))·6H(2)O or Co(ClO(4))·6H(2)O as the metal source, it gives the mixed bridged hexanuclear complex [(dpk·OMe)(4)(dpk·NCN)(2)Cu(6)(H(2)O)(2)](ClO(4))(4) (4), or the mononuclear complex [(dpk·OMe)(dpk·HNCN)Co](ClO(4))·2H(2)O (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.