Crystal structure, spectroscopic and magnetic properties of the complex [Cu(paphy)(NCS)(SCN)](paphy = pyridine-2-carbaldehyde 2′-pyridylhydrazone). An unusual di-µ-thiocyanato-N bridged copper( II ) dimer

The crystal and molecular structure of [Cu(paphy)(NCS)(SCN)](paphy = pyridine-2-carbaldehyde 2′-pyridylhydrazone) has been determined from three-dimensional X-ray data. It crystallizes in the monoclinic space group P21/a with four formula units in a cell of dimensions a= 15.778(3), b= 9.937(2), c= 9.795(3)Å, and β= 91.31(2)°. Least-squares refinement of 1 163 reflections with I 2.5σ(I) gave a final R= 0.073 (R′= 0.073). The structure consists of isolated centrosymmetric [Cu(paphy)(NCS)(SCN)]2 dimeric units where the two copper(II) ions are linked in an unusual way through the N end of two N-thiocyanate bridging groups. The resulting co-ordination geometry around each copper(II) ion is elongated tetragonal octahedral. The N bridging atoms occupy simultaneously an equatorial position in the co-ordination sphere of one of the copper atoms and an axial one in the other. The remaining axial positions are occupied by sulphur atoms of the S-bonded thiocyanate groups. Magnetic susceptibility measurements down to 2.8 K and e.s.r. spectra provide evidence of the existence of very weak exchange coupling. These results are discussed on the basis of the structural features. A comparison is made with previously published data on related copper(II) thiocyanate complexes.