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 {Cu 3 I 6 3- } n (R = H), {Cu 2 I 3 - } n (R = Me), {Cu 3 I 4 - } n (R = Et), {Cu 6 I 8 2- } n (R = Pr), and {Cu 5 I 7 2- } n (R = Bu, Pn, Hx). The [N-Bu-3-PyX] + ions were typically paired with the 1-D chain {Cu 5 I 7 2- } n . 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.