SYNTHESIS, STRUCTURAL CHARACTERIZATION AND STUDIES OF OCTANUCLEAR COPPER-COMPLEXES OF PYRIDONATE AND CARBOXYLATE LIGANDS

A series of octanuclear copper(II) complexes has been prepared which f eatures carboxylate and 2-pyridonate ligands. These compounds have the general formula [CU8(O)(2)(O(2)CR)(4)L(8)] (where R = Me, Ph or CF3, and L = 6-chloro-. 6-bromo- or 6-methyl-2-pyridonate). X-Ray structura l analyses of the acetate complexes indicate that the compounds contai n an edge-sharing Cu,O, bitetrahedral core, surrounded by two [CuL(4)] units. The Cu ...Cu contacts within the core vary from 2.92 to 3.58 A ngstrom, depending on the ligand bridging the metal-metal vector. Two routes to these complexes have been investigated, one involving reacti on of preformed copper pyridonate complexes with copper carboxylates, the second involving reaction of copper carboxylates with molten HL. D ifferential scanning calorimetry and thermogravimetric analysis studie s of the latter route show it proceeds via formation of copper pyridon ate complexes. The FAB mass spectral results show interesting fragment ation patterns, consistent with the observed structures, and NMR spect ra of the octanuclear complexes show paramagnetically shifted resonanc es due to both the pyridonate and carboxylate ligands. Magnetic studie s of [Cu-8(O)(2)(O(2)CMe)(4)L(8)] (L = 6-chloro- or 6-bromo-2-pyridona te) show largely antiferromagnetic exchange coupling within the Cu6O2 core. The structure of the complexes and the magnitude of the coupling s lead to spin-frustrated systems, with subtle differences between the two complexes studied.