Zwitterionic π-coordination compounds of copper(I) with monosubstituted alkynes: synthesis, crystal and electronic structure of two copper(I) halide π-complexes with 4-amino-1-propargylpyridinium

Abstract

Crystals of two mononuclear π-coordination compounds of copper(I) halide with 4-amino-1-propargylpyridinium cation – [(HC≡CCH2NC5H4NH2)CuBr2] (1) and [(HC≡CCH2NC5H4NH2)CuCl1.61 Br0.39] (2) – were obtained in the CuX–H2O–(HC≡CCH2NC5H4 NH2)Br system (HC≡CCH2N+C5H4NH2 is 4-amino-1-propargylpyridinium cation (app +), X=Cl or Br). The purity and identity of the synthesized compounds were verified by elemental analysis and IR spectroscopy. The compounds were structurally characterized using X-ray single crystal method and are isostructural. Both crystals are built of zwitterionic appCuX 2 units, in which triple C≡C bond is coordinated to only one copper(I) ion. The Cu–m distance (m is the middle of the C≡C bond) is 1.933(5) and 1.917(3) Å for 1 and 2, respectively. The predisposition of copper(I) halides to coordination polymer self-assembly through Cu–X···Cu bridge formation is not realized in 1 and 2. However, the ≡C–H···Х and N–H···Х hydrogen bonds along with π–π stacking of 4-aminopyridinium groups compensate an absence of the structure-forming interaction Cu–X···Cu. DFT calculations of an electron structure of [(app)CuCl2] were carried out (the restricted Hartree–Fock (RHF) method with a 6–31 G* orbital basis set). Calculated values of the charge density distribution on atoms as well as the constructed molecular orbitals (MOs) are in agreement with stereochemical parameters of the (Cu(I)–(C≡C))-core of both coordination compounds.