The first structural evidence of a polymeric Cu(II) compound with a bridging dicyanamide anion: X-ray structure, spectroscopy and magnetism of catena-[polybis(2-aminopyrimidine)copper(II)bis(μ-dicyanamido)]

The new Cu(II) coordination compound, catena-[Cu(N(CN)2)2(ampym)2] (in which ampym=2-aminopyrimidine) has been synthesized and investigated by X-ray analysis, ligand field, EPR spectroscopy and magnetic susceptibility. The first compound crystallizes in the monoclinic space group C2/c with a=13.579(6), b=15.453(5), c=7.570(7) Å, β=92.03(5)° and refines to an R value of 0.0322. The geometry around the copper(II) atom is axially elongated octahedral with the basal plane formed by the nitrogen of two monodentate coordinating ligands and two (N2) nitrogens of the bridging dicyanamide anions with distances which vary from 1.972(3) to 2.078 Å forming an almost perfect square planar geometry. The apical positions are occupied by the other nitrogens (N3) of the bridging dicyanamide anions with a distance of 2.416(3) Å. The bridging dicyanamide forms a one-dimensional polymeric chain with the other copper units. The CuCu separation is 7.570 Å. Hydrogen bonding (3.1231 Å) between the hydrogen atoms of the amino nitrogen and the uncoordinated nitrogen of the ligand forming pairs of ligands stabilizes the lattice, and bridges the chain in 2D-sheets. A Ligand field maximum occurs at 14.3×103 cm−1 and the EPR values, measured as a solid, are g⊥=2.08 and g//=2.29. Magnetic susceptibility of the powdered sample was measured from 4 to 300 K. The inverse susceptibility versus temperature shows that the curve follows the Curie–Weiss law. The μeff versus temperature gives a negligible rise at lower temperature and stays constant at about 1.80–1.84. The characteristic infrared vibrations for the dicyanamide anion are the νs+νas(CN), found as one strong band at 2301 cm−1, and the ν(CN), found as two strong bands at 2254 and 2188 cm−1.