Structure and magnetic exchange in poly-bis(pyrazine)bis(methanesulfonato-O)-copper(II). One-dimensional exchange in a two-dimensional polymer

Crystals of poly-bis(pyrazine)bis(methanesulfonato-O)copper(II) are orthorhombic, a = 8.199(1), b = 13.130(1), c = 6.913(1) Å, Z = 2, space group Pnnm. The structure was solved by conventional heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.025 and Rw = 0.033 for 1226 reflections with I ≥ 3σ(I). The complex contains parallel sheets, each sheet consisting of a square array of copper(II) ions bridged by two types of bidentate pyrazine ligands. The CuN4O2 chromophore is tetragonally elongated; the equatorial plane contains two pyrazine nitrogen atoms (Cu—N(1) = 2.058(2) Å) and two oxygen atoms from monodentate methanesulfonate ligands (Cu—O(1) = 1.956(1) Å); the axial sites are occupied by bridging pyrazine groups with significantly longer Cu—N bond lengths (Cu—N(2) = 2.692(2) Å) Magnetic susceptibility studies (82 to 4.2 K) reveal antiferromagnetic behaviour with a susceptibility maximum at about 6.2 K. Exchange coupling in the complex is considered to take place primarily via the more strongly bound, equatorially coordinated pyrazine ligands. Analysis of the magnetic susceptibility data according to a Heisenberg linear chain of interacting S = 1/2 spins yields best fit values of J = −3.82 cm−1 and g = 2.13. Vibrational and electronic spectroscopic and differential scanning calorimetric studies on the title compound and, for comparison, on the related mononuclear pyridine complex, bis(methanesulfonato)-tetrakis(pyridine)copper(II), are also reported.