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.

The structures of three tetramethylammonium cyanocuprate(I) 3D networks [NMe4]2[Cu(CN)2]2•0.25H2O (1), [NMe4][Cu3(CN)4] (2), and [NMe4][Cu2(CN)3] (3), (Me4N = tetramethylammonium), and the photophysics of 1 and 2 are reported. These complexes are prepared by combining aqueous solutions of the simple salts tetramethylammonium chloride and potassium dicyanocuprate. Single-crystal X-ray diffraction analysis of complex 1 reveals {Cu2(CN)2(μ2-CN)4} rhomboids crosslinked by cyano ligands and D3h {Cu(CN)3} metal clusters into a 3D coordination polymer, while 2 features independent 2D layers of fused hexagonal {Cu8(CN)8} rings where two Cu(I) centers reside in a linear C∞v coordination sphere. Metallophilic interactions are observed in 1 as close Cu⋯Cu distances, but are noticeably absent in 2. Complex 3 is a simple honeycomb sheet composed of trigonal planar Cu(I) centers with no Cu…Cu interactions. Temperature and time-dependent luminescence of 1 and 2 have been performed between 298 K and 78 K and demonstrate that 1 is a dual singlet/triplet emitter at low temperatures while 2 is a triplet-only emitter. DFT and TD-DFT calculations were used to help interpret the experimental findings. Optical memory experiments show that 1 and 2 are both optical memory active. These complexes undergo a reduction of emission intensity upon laser irradiation at 255 nm although this loss is much faster in 2. The loss of emission intensity is reversible in both cases by applying heat to the sample. We propose a light-induced electron transfer mechanism for the optical memory behavior observed.

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