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)CuCl_1.61 Br_0.39] (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 appCuX₂ 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.

Keywords:

• Synthesis
• alkyne copper(I) π-coordination compounds
• XRD analysis
• DFT studies
• π–π stacking
• hydrogen bonds

Acknowledgements

We thank Professor T. Lis, a colleague from Wroclaw University, for his great help in obtaining and analyzing X-ray diffraction data.

Disclosure statement

No potential conflict of interest was reported by the authors.