Dinuclear and tetranuclear copper(I) iodide complexes with P and P^N donor ligands: Structural and photoluminescence studies

In order to investigate photophysical properties and crystallization medium effects, three Cu complexes, [CuI(PCy3)]2 (1), [Cu(I)(PPh2Me)]4 (2), and [Cu4(I)4(PPh2py)2] (3) were prepared and characterized using single crystal X-ray crystallography, solid state NMR, UV–Vis, and IR spectroscopy. In 1, as previously reported, Cu2I2 core is a square dimer with alternating copper and iodides positioned in the corners. Each copper atom is surrounded by two bridging iodides and a terminal tricyclohexylphosphine ligand. The cluster 2 adopts a cubane-like Cu4I4 core, while in cluster 3 (as thf solvate) a Cu4I2 distorted octahedral core is decorated with two bridging iodides and two chelating P^N ligands. The solid state 31P NMR analysis showed the presence in the powder of several polymorphs, the most abundant of which being, in the case of 2, the cubane-like structure resolved by XRD methods, and in the case of 3, a butterfly structure, different from that found for 3·thf. The solid state blue photoluminescence intensity in 1 is dependent upon its poly- or single-crystallinity. While dimer 1 in polycrystalline form is a stronger blue light emitter under 254 nm light irradiation than in 365 nm, in single crystalline phase it shows a similar higher intensity blue luminescence under lower energy light (365 nm) irradiation. On the other hand, clusters 2 and 3 do not show phase-dependent luminescence intensity variation. Time-dependent Density Functional Theory (TD-DFT) showed that the emission in 1 and 3 is assigned to a mixed metal to ligand and halide to ligand charge transfer, (X + M)LCT. In 2, a dual emission band at low temperature was observed which was attributed to 3CC (LE band) and 3XLCT (HE band). Thermochromism and mechanochromism of complexes 1–3 were also investigated.