Three-Dimensional Mixed-Ligand Coordination Polymers with Ferromagnetically Coupled Cyclic Tetranuclear Copper(II) Units Bonded by Weak Interactions

The complexes {[Cu (HGLYO)(NO3)(bpy)]center dot H2O}(4) (1), {[Cu(HGLYO)(NO3)(phen)]center dot H2O}(4) (2), and [Cu(HLACO)(ClO4)(phen)](4) (3) (bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, HGLYO is monoanionic glycolate, and HLACO is monoanionic lactate) have been synthesized and their crystal structures were determined by X-ray diffraction analysis. The thermal behavior and IR, electronic and electron paramagnetic resonance (EPR) spectra are also reported. The structures of compounds 1-3 consist of cyclic tetrameric units in which the copper(II) ions are connected by carboxylate groups in an anti-syn conformation. The hydroxycarboxylates, diimine ancillary ligancls, and crystallization water molecules when have a significant influence on the crystal structures through weak interactions such as hydrogen bonding and pi-pi stacking. These interactions mainly contribute to the stabilization of the overall supramolecular structures, which contain rectangular voids of different dimensionality. Magnetic measurements in the temperature range 1.8-300 K showed that compounds 1 and 2 are ferromagnetic. The J values obtained were 3.2 cm(-1) for 1 and 3.3 cm(-1) for 2. An electrochemical study for complexes 1 and 2 by cyclic voltammetry in dimethylformamide solutions showed the irreversible nature of the electrode process.