Synthesis, crystal structure and magnetic properties of a polymeric copper(II) Schiff-base complex having binuclear units covalently linked by isonicotinate ligands

The polynuclear copper(II) complex [{Cu2L(O2CC5H4N)}. C2H5OH](x) (1), where H3L is a 1∶2 Schiff base derived from 1,3-diaminopropan-2-ol and sal icylaldehyde, has been prepared and structurally characterized. The structu re consists of a one-dimensional zigzag chain in which the binuclear [Cu2L] (+) units are covalently linked by isonicotinate ligands to give a syndiota ctic arrangement of the copper ions protruding outside the chain. In the ba sic unit, the copper(II) centres are bridged by an alkoxo and a carboxylato ligand, giving a Cu ... Cu distance of 3.492(3) Angstrom and a Cu-O-Cu ang le of 130.9(2)degrees. While one copper centre has a square-planar geometry , the other copper is square-pyramidal with the pyridine nitrogen being the axial ligand. The visible electronic spectrum of 1 shows a broad d-d band at 615 nm. The complex shows a rhombic X-band EPR spectral pattern in the p olycrystalline phase at 77 K. Magnetic susceptibility measurements in the t emperature range 22 to 295 K demonstrate the antiferromagnetic behaviour of 1. A theoretical fit to the magnetic data is based on a model assuming 1 a s an equimolar mixture of copper atoms belonging to an antiferromagneticall y coupled one-dimensional Heisenberg chain with the other copper atoms outs ide the chain behaving like paramagnetic centres.