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 {Cu3I63–}n (R = H), {Cu2I3–}n (R = Me), {Cu3I4–}n (R = Et), {Cu6I82–}n (R = Pr), and {Cu5I72–}n (R = Bu, Pn, Hx).
The [N-Bu-3-PyX]+ ions were typically paired with the 1-D
chain {Cu5I72–}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.