Alkyl Pyridinium Iodocuprate(I) Clusters: Structural Types and Charge Transfer Behavior

The reaction of copper(I) iodide (CuI) and N-alkyl pyridinium (RPy⁺, R = H, Me, Et, n-propyl = Pr, n-butyl = Bu, n-pentyl = Pn, and n-hexyl = Hx) or N-butyl-3-substituted pyridinium (N-Bu-3-PyX⁺, X = I, Br, Cl, CN, and OMe) iodide salts yielded pyridinium iodocuprate(I) salts. Crystal structures of iodocuprate ions coupled with RPy⁺ include {Cu₃I₆ ^3-} (R = H), {Cu₂I₃ ^-} (R = Me), {Cu₃I₄ ^-} (R = Et), {Cu₆I₈ ^2-} (R = Pr), and {Cu₅I₇ ^2-} (R = Bu, Pn, Hx). The [N-Bu-3-PyX]⁺ ions were typically paired with the 1-D chain {Cu₅I₇ ^2-} . Diffuse reflectance spectroscopy performed on the [N-Bu-3-PyX]⁺ iodocuprate salts revealed that increasing the electron withdrawing capacity of the [N-Bu-3-PyX]⁺ system reduced the absorption edge of the iodocuprate salt. Variable temperature emission spectra of several [N-Bu-3-PyX]⁺ compounds revealed two emission peaks, one consistent with a cluster-centered halide to metal charge transfer and the other consistent with an intermolecular mixed halide/metal charge transfer to the organic cation. The emission intensity and emission wavelength of the mixed halide/metal to cation charge transfer depends on the organic cation substitution.