Pentanuclear copper(II) complexes with the novel 6-(phenylethynyl)-2-pyridonate ligand: synthesis, structures and magnetic properties

Abstract

Three pentanuclear copper(II) complexes, [Cu ₅ (OMe) ₂ (CF ₃ CO ₂ )(pehp) ₆ (Cl)] 1, [Cu ₅ (OMe) ₂ (CF ₃ CO ₂ )(pehp) ₆ (NO ₃ )] 2 and [Cu ₅ (OH)(CF ₃ CO ₂ ) ₃ (pehp) ₆ ] 3, have been prepared via the solid-state reaction of hydrated copper(II) nitrate with the sodium salt of the novel ligand, 6-(phenylethynyl)-2-pyridone (Hpehp) in the presence of sodium trifluoroacetate. Crystal structural analysis at 220 K of 1–3 reveals capped-butterfly arrangements of the five copper atoms with the two shortest Cu · · · Cu vectors in 1 and 2 [3.024(6)–3.050(3) Å] occurring between the caps and the wingtips while in 3 the wingtip–cap distances are more asymmetric with one short [3.042(7) Å] and one long [3.638(7) Å] Cu · · · Cu vector. Mass spectroscopic studies of 1–3 show fragmentation patterns consistent with the observed structures, while magnetic studies of the complexes indicate antiferromagnetic exchange coupling within the Cu ₅ cores and S = ½ ground states for all compounds. The trifluoroacetate adduct of Hpehp, Hpehp·0.5CF ₃ CO ₂ H was synthesised in three steps from 2-bromo-6-benzyloxypyridine via 2-benzyloxy-6-(phenylethynyl)pyridine and the single crystal X-ray structure of Hpehp was also determined.