New copper carboxyl-ate pyrene dimers: synthesis, crystal structure, Hirshfeld surface analysis and electrochemical characterization

Abstract

Two new copper dimers, namely, bis-(dimethyl sulfoxide)-tetra-kis-(μ-pyrene-1-carboxyl-ato)dicopper(Cu-Cu), [Cu₂(C₁₇H₉O₂)₄(C₂H₆OS)₂] or [Cu₂(pyr-COO^-)₄(DMSO)₂] (1), and bis-(di-methyl-formamide)-tetra-kis-(μ-pyrene-1-carboxyl-ato)dicopper(Cu-Cu), [Cu₂(C₁₇H₉O₂)₄(C₃H₇NO)₂] or [Cu₂(pyr-COO^-)₄(DMF)₂] (2) (pyr = pyrene), were synthesized from the reaction of pyrene-1-carb-oxy-lic acid, copper(II) nitrate and tri-ethyl-amine from solvents DMSO and DMF, respectively. While 1 crystallized in the space group P , the crystal structure of 2 is in space group P2₁/n. The Cu atoms have octa-hedral geometries, with four oxygen atoms from carboxyl-ate pyrene ligands occupying the equatorial positions, a solvent mol-ecule coordinating at one of the axial positions, and a Cu⋯Cu contact in the opposite position. The packing in the crystal structures exhibits π-π stacking inter-actions and short contacts through the solvent mol-ecules. The Hirshfeld surfaces and two-dimensional fingerprint plots were generated for both compounds to better understand the inter-molecular inter-actions and the contribution of heteroatoms from the solvent ligands to the crystal packing. In addition, a Cu²⁺/Cu¹⁺ quasi-reversible redox process was identified for compound 2 using cyclic voltammetry that accounts for a diffusion-controlled electron-donation process to the Cu dimer.

Keywords: carboxyl­ate; crystal structure; dicopper; pyrene; π–π stacking.