Preparation and characterization of azaindolyl-azaindole and structure of its halogen-free dicationic cluster containing the µ 4 -oxotetracopper(II) core

Refluxing NbCl 5 and excess 7-azaindole (Haza) in benzene yielded a solid mixture containing NbCl 5 (Haza), NbCl 4 (Haza) 2 , the azaindolium ion (H 2 aza) + , and the azaindolyl-azaindolium ion (H 2 aza-aza) + . The neutral (Haza-aza) molecule was obtained from the hydrolysed mixture and shown by X-ray diffraction (monoclinic, P2 1 /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 [Cu 4 O(aza-aza) 4 ]Cl 2 • 6.5H 2 O were obtained from (Haza-aza) and CuCl 2 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 µ 4 -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 1 H NMR and infrared spectroscopy data are discussed.