Pentafluorophenyl Copper–Pyridine Complexes: Synthesis, Supramolecular Structures via Cuprophilic and π-Stacking Interactions, and Solid-State Luminescence

The effect of the binding of pyridine ligands to pentafluorophenyl copper, [C6F5Cu]4 (1), on structural features and photophysical properties has been investigated through a combined multinuclear NMR, X-ray crystallography, and photoluminescence study. Reaction of 1 with 2 equiv of pyridine yields a novel pyridine complex, 3, in which the tetranuclear framework of 1 is retained. Complex 3 features a rhombus-shaped tetracopper core with a short diagonal Cu···Cu distance of 2.5941(6) Å between the dicoordinate copper centers and a longer distance between the pyridine-coordinated copper centers of 4.178(1) Å. In contrast, treatment of 1 with 4 equiv of pyridine results in complete breakdown of the tetranuclear aggregate to give the formally dicoordinate species C6F5Cu(py) (4-H). Reaction of 1 with 2,2′-bipyridine results in formation of the tricoordinate complex C6F5Cu(2,2′-bipy) (5). Aggregate breakdown in species 4 and 5 is reflected in a significantly reduced chemical shift difference Δδ(19Fmeta/para) and a strong downfield shift of the copper-bound carbon atoms in the 13C NMR spectra in comparison to 3. A dynamic equilibrium is established at ratios of py/C6F5Cu ranging from 0 to 2. The solid-state structures of all compounds have been determined by single-crystal X-ray crystallography. The supramolecular assembly of complex 3 via arene–arene π-interactions leads to a network structure with solvent-filled channels propagating through the lattice along the crystallographic c axis. The 2,2′-bipyridine complex 5 also shows π-stacking as the dominant feature in the extended solid-state structure. In contrast, a different mode of supramolecular assembly is found for 4-H in that cuprophilic interactions lead to assembly into one-dimensional copper chains with equidistant Cu···Cu contacts of 2.8924(3) Å. However, the closely related complexes 4-R with methyl or chloro substituents in either the ortho or the para position form supramolecular stacks with structural features that, again, are dominated by offset perfluoroarene–arene interactions with intermolecular plane-to-plane separations of ca. 3.3–3.6 Å. The dicoordinate copper atoms are aligned in one-dimensional chains with alternating short and long Cu(I)···Cu(I) distances of 3.531(1)/3.698(1) Å in 4-pMe, 3.2454(5)/4.2970(5) Å in 4-oMe, 3.521(1)/3.784(1) Å in 4-pCl, and 3.4797(6)/3.8363(6) Å in 4-oCl. Compound 4-H is strongly blue fluorescent at 460 nm in the solid state, but yellow-green fluorescent at 77 K