Preparation and structure of 7-azaindolium salts containing unusual chloro-copper(II) anionic units

Abstract

Dark-red crystals of (H2aza)5[Cu5Cl14(H2O)4]Cl were obtained by addition of HCl to equimolar amounts of 7-azaindole (Haza) and CuCl2•2H2O in methanol. They were shown by X-ray diffraction (triclinic, [Formula: see text] a = 9.396(1), b = 9.894(1), c = 15.958(1), Å, α = 106.10(1)°, β = 98.25(1)°, γ = 105.56(1)°, Z = 1, R = 0.031) to contain infinite chains in which the basic [Cu5Cl14(H2O)4]4− pattern is built up from trans-CuCl2(H2O)2, [CuCl3(H2O)]−, and dichlorobridged [Cu2Cl6]2− species. In the idealized chain, these units occur in the 1:2:1 ratio, but disorder is present and some of the CuCl2(H2O)2 units are randomly replaced by [CuCl3(H2O)]−. The Cu atoms have a roughly square-planar primary coordination, and connection along the chain is achieved by weaker apical Cu–Cl bridging interactions. All azaindole molecules are present as uncoordinated N7-protonated monocations. A related (H2aza)3[Cu3Cl8(H2O)3]Cl salt was obtained as a side-product of the reaction of 7-azaindole with excess CuCl2•2H2O in methanol without acid. In these brown crystals (triclinic, [Formula: see text] a = 9.308(1), b = 9.964(1), c = 19.212(4) Å, α = 76.67(1)°, β = 79.35(1)°, γ = 75.27(1)°, Z = 2, R = 0.046), the [Cu6Cl16(H2O)6]4− pattern of the chain contains the same three building units as above, but in the 2:2:1 ratio. In both salts, the polymeric chloro-copper chains are parallel and separated by azaindolium cations stacked along the same direction. The structures are stabilized by networks of hydrogen bonds involving the azaindolium cations, the chlorine atoms, and water molecules in the chloro-copper chain, and a noncoordinated Cl− ion. Most of the azaindolium cations are disordered. The influence of N7-protonation on the infrared spectrum of azaindole is discussed.