Crystal structure and magnetic behavior of a copper(II)-(pyrazine 2,3-dicarboxylate) coordination polymer: 3D architecture stabilized by H-bonding

Reaction of Cu(ClO4)2 · 6H2O and pyrazine 2,3-dicarboxylate (pzdc) in aqueous ammonia medium results [Cu(pyrazine 2,3-dicarboxylate)(H2O)2] · H2O (1). The X-ray single crystal structure reveals that the compound is a 1D polymeric sinusoidal infinite chain which through intra- and inter-molecular hydrogen bonding interactions, involving lattice and coordinated water molecules with dicarboxylate oxygens and pyrazine nitrogens, gives rise to a 3D architecture. The variable temperature magnetic measurements show weak antiferromagnetic interactions between the Cu(II) centers. The best fit parameters through the typical equation for a uniform copper (II) chain are: J=−0.25 cm−1, g=2.17, R=1.3×10−6. The EPR spectrum does not alter with temperature (from r.t. to 4 K). The spectra are typical for square-pyramidal geometry of copper(II) ions, g∥=2.24 and g⊥=2.10 (average g=2.15, in good agreement to the value obtained by susceptibility fit).