Subtle Modulation of Cu<sub>4</sub>X<sub>4</sub>L<sub>2</sub> Phosphine
Cluster Cores Leads to Changes in Luminescence
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Abstract
A series
of Cu<sub>4</sub>X<sub>4</sub>(PPh<sub>2</sub>py)<sub>2</sub> compounds
(X = Cl (<b>1</b>), Br (<b>2</b>), I (<b>3</b>),
PPh<sub>2</sub>py = 2-(diphenylphosphino)pyridine) were prepared and
characterized using X-ray crystallography, NMR, UV–vis, and
luminescence spectroscopy. The copper chloride and bromide clusters
have Cu<sub>4</sub>X<sub>4</sub> octahedral cores while the copper
iodide clusters contain an unprecedented butterfly shaped core. Crystallization
of the copper bromide and iodide clusters from the appropriate solvent
produced the solvates <b>2</b>·2CH<sub>2</sub>Cl<sub>2</sub>, <b>2</b>·2CHCl<sub>3</sub>, and <b>3</b>·0.5CH<sub>2</sub>Cl<sub>2</sub> where the presence of the lattice solvate influences
the overall structural properties. Using TD-DFT calculations, the
emission was assigned to a mixed metal- and halide-to-ligand charge
transfer, (M + X)LCT. Subtle differences in the copper core geometry
and μ-halide bonding perturb the emissions of these copper(I)
halide clusters
