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

4-Methyl-5-imidazolecarboxyaldehyde (HL1) reacts with copper(II) perchlorate to give the complex [Cu(HL1)(3)](ClO4)(2). Its X-ray structure reveals that three ligands are bonded to the copper(II) ion in a bidentate chelate fashion through the imidazole nitrogens and aldehyde oxygen atoms, leading to a CuN3O3 chromophore. Carbonyl co-ordination to copper(II) is not usual, in fact there are very few reported examples of structurally characterised complexes of this type. When [Cu(HL1)(3)](ClO4)(2) is dissolved in a KOH-containing methanol solution, the polymer [Cu(L-1)(2)](n) precipitates. The magnetic properties of [Cu(L-1)(2)](n) are typical of an imidazolate-bridged copper(II) system in which the bridge involves equatorial positions on the copper(II) 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(HL1)(3)](ClO4)(2) react with 1,3-diaminopropane, leading to a new monomeric Schiff-base copper(II) 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.