Preparation and characterization of azaindolyl-azaindole and structure of its halogen-free dicationic cluster containing the µ4-oxotetracopper(II) core

Abstract

Refluxing NbCl5 and excess 7-azaindole (Haza) in benzene yielded a solid mixture containing NbCl5(Haza), NbCl4(Haza)2, the azaindolium ion (H2aza)+, and the azaindolyl-azaindolium ion (H2aza-aza)+. The neutral (Haza-aza) molecule was obtained from the hydrolysed mixture and shown by X-ray diffraction (monoclinic, P21/c, a = 10.025, b = 13.758, c = 8.416 Å, β = 102.89°, Z = 4, R = 0.035) to result from the coupling of two azaindole units via N7—C6′. This compound was the only oxidation product detected, but concurrent formation of other niobium- and (or) azaindole-containing products keeps the yield of Haza-aza low. Dark green crystals of [Cu4O(aza-aza)4]Cl2•6.5H2O were obtained from (Haza-aza) and CuCl2 in wet methanol. The crystal structure (monoclinic, C2/c, a = 17.704, b = 25.240, c = 14.457 Å, β = 116.14°, Z = 4, R = 0.051) shows the presence of a tetranuclear dicationic cluster consisting of a µ4-oxide ion surrounded by a tetrahedron of Cu(II) atoms. A distorted square-planar coordination is achieved about each copper atom by (aza-aza)− ligands each bridging two copper atoms and providing a third nitrogen donor to one of them. For each such cation, the unit cell also includes two chloride ions and 6.5 disordered lattice water molecules. The 1H NMR and infrared spectroscopy data are discussed.