Magnetic properties and crystal structure of a one-dimensional phase of tetrakis(μ2-benzoato-O,O′)-bis(dimethyl sulfoxide)dicopper(II)

A new crystalline polymorphic phase of tetrakis(μ₂-benzoato- O,O′)-bis(dimethyl sulfoxide)dicopper(II) was obtained by direct synthesis, in space group P2₁/n. The copper coordination is in a slightly distorted square pyramidal geometry with an intramolecular Cu⋯Cu distance of 2.6494(8) Å. The Cu-O distances of the two copper in a dimer are different, giving different chemical environments for each Cu ion. The crystal structure is built up of well-separated stacking columns oriented along the b-axis, with units uniformly spaced, producing a one-dimensional (1-D) zigzag chain through Cu(II)-S⋯S-Cu(II) interdimer interactions [S⋯S separation: 3.975(2) Å]. Magnetization measurements in the range 2-300 K indicate two magnetic orderings, at low temperature (T < 10 K) a weak ferromagnetic ordering is observed, and above this temperature an antiferromagnetic behavior takes place. ESR spectra at 300 and 77 K of a polycrystalline sample show the characteristic signal of zero-field with D = 0.354 cm^-1, consistent with a ferromagnetic Cu⋯Cu exchange interaction at low temperature.