Alkyl pyridinium iodocyanocuprate(i) chains (RPy)2[Cu2I3(CN)]: insight into structural, electronic and spectroscopic properties

Abstract

Equimolar mixtures of copper(I) iodide (CuI) and copper(I) cyanide (CuCN) react with N-alkyl pyridinium iodides (RPy⁺I⁻, R = Me, Et, n-propyl = Pr, and n-butyl = Bu) to produce pyridinium iodocyanocuprate(I) salts, (RPy)₂[Cu₂I₃CN]. Crystal structures reveal isostructural anionic chains consisting of trigonal pyramidal Cu₂(μ₂-I)₃ clusters bridged by C/N-disordered cyano units. The 1-D chains are nearly linear but vary with respect to whether adjacent clusters are staggered or eclipsed. A detailed investigation via Hirshfeld surface analysis reveals that hydrogen bonding between the triiodide group and pyridinium cation are the driver for assembly in these systems. Interestingly, spectroscopic investigations of absorption edge and emission energies show a general red shift with increasing hydrogen bonding. DFT and TD-DFT calculations were used to determine the electronic structure and band assignment of these materials to elucidate the nature behind this structure/function relationship.