A tris-imidazolecarboxyaldehyde copper(II) complex with unusual carbonyl co-ordination: structure and reactivity

4-Methyl-5-imidazolecarboxyaldehyde (HL) reacts with copper() perchlorate to give the complex [Cu(HL)3](ClO4)2. Its X-ray structure reveals that three ligands are bonded to the copper() ion in a bidentate chelate fashion through the imidazole nitrogens and aldehyde oxygen atoms, leading to a CuN3O3 chromophore. Carbonyl co-ordination to copper() is not usual, in fact there are very few reported examples of structurally characterised complexes of this type. When [Cu(HL)3](ClO4)2 is dissolved in a KOH-containing methanol solution, the polymer [Cu(L)2]n precipitates. The magnetic properties of [Cu(L )2]n are typical of an imidazolate-bridged copper() system in which the bridge involves equatorial positions on the copper() co-ordination polyhedra. A J value of 58.1 cm 1 was calculated by application to the experimental data of the theoretical equation for a uniform one-dimensional infinite chain system. Additionally, the co-ordinated carbonyl groups of [Cu(HL)3](ClO4)2 react with 1,3-diaminopropane, leading to a new monomeric Schiff-base copper() complex. However, this reaction does not take place when the diamine is 1,2-diaminopropane, which is likely due to the sterically promoted low reactivity for imine bond formation with the –NH2 group close to the methyl substituent in 1,2-diaminopropane.