Trinuclear copper(<scp>i</scp>) furanyl <i>ortho</i>-diphosphine halide clusters: structure, photophysical and photocatalytic hydrogen production properties

In recent years, mono- and di-nuclear copper(I) <i>ortho</i>-diphosphine halide complexes have attracted much attention due to their excellent emissive properties. However, trinuclear copper(I) <i>ortho</i>-diphosphine halide clusters have not been reported so far. Herein, three trinuclear Cu(I) furanyl <i>ortho</i>-diphosphine halide clusters Cu₃X₃(dppf)₂ [X = I (1), Br (2), Cl(3), dppf = 3,4-bis(diphenylphosphino)furan] were successfully synthesized, and their molecular structures and photophysical properties were systematically studied. The structures of complexes 1-3 reveal that three Cu(I) and two μ₃-X ions form a trigonal bipyramid, in which three Cu(I) ions form a plane, with two μ₃-X ions above and below the plane, respectively. One side of the triangle is bridged by one μ₂-X ion, while each of the other two sides is bridged by one dppf ligand. At 297 K, complexes 1 and 2 in the powder state emit yellowish orange light with broad bands (1: <i>λ</i>_em = 644 nm, <i>τ</i> = 1.3 μs, <i>Φ</i> = 7.79%; 2: <i>λ</i>_em = 614 nm, <i>τ</i> = 14.0 μs, <i>Φ</i> = 9.27%) and complex 3 in the powder state shows greenish blue delayed fluorescence (<i>λ</i>_em = 472 nm; <i>τ</i> = 9.4 μs; <i>Φ</i> = 10.63%). The broad emission bands of complexes 1 and 2 at 297 K are due to ³XLCT (halogen-to-ligand charge transfer) and cluster-centered phosphorescence (³CC). The emission of complex 3 at 297 K mainly originates from MLCT (metal-to-ligand charge transfer) and ILCT (intraligand charge transfer). Under visible-light irradiation, complexes 1-3 displayed photocatalytic H₂ evolution activity. Complex 3 showed the highest hydrogen production rate of 223.2 μmol g^-1 h^-1 and good photostability.