Synthesis, structural characterisation, electron paramagnetic resonance and magnetic studies of homoleptic copper complexes of pyridonate ligands

Three homoleptic copper(II) complexes have been prepared which feature 6-halogen-substituted 2-pyridonate ligands [{Cu2(xhp)4}n](n= 1, xhp = 6-chloro- or 6-bromo-2-pyridonate; n= 2, xhp = 6-fluoro-2-pyridonate). X-ray structural analysis of the complexes showed that for the chlorine- and bromine-substituted derivatives a dinuclear complex forms where the xhp ligands are arranged to give a dimeric unit with idealised D2d symmetry. For the fluorine-substituted ligand smaller steric requirements allow rearrangement to occur to give dinuclear units with approximate C4v symmetry, which can then dimerise giving tetrametallic molecules. The Cu ⋯ Cu contacts within these species are around 2.5 A, and to investigate the nature of the Cu ⋯ Cu interaction variable-temperature EPR and magnetic studies were carried out. These revealed strong antiferromagnetic exchange between the S=½ centres; EPR also revealed a weak interdimer exchange which was not evident from susceptibility measurements.

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