Synthesis and structural characterization of luminescent gold( i ) derivatives with an unsymmetric diphosphine

We have synthesised a series of mono-bridged digold(I) derivatives with an unsymmetric diphosphine, namely, [(AuX)2(μ-PiPr2CH2PPh2)] (X = Cl, Br, I, C6F5, S2CN(CH2Ph)2) and the mononuclear gold(III) complex [Au(C6F5)3(PiPr2CH2PPh2)]. X-ray diffraction studies show intramolecular gold(I)–gold(I) interactions of 3.4179(2), 3.1660(2) and 3.0926(3) Å, respectively, for X = Cl, Br and C6F5. The pentafluorophenyl derivative emits at 445 nm at room temperature in the solid state; this compound and the halo-derivatives are emissive at low temperature in the range 440–486 nm. We have also prepared doubly-bridged diauracycles, namely, [Au2X2(μ-PiPr2CH2PPh2)2] (X = Cl, Br, I) and [Au2(μ-PiPr2CH2PPh2)2]A2 (A = CF3SO3, ClO4). The crystal structure of the iodo derivative displays three-coordinated gold centres in a T-shaped geometry, with a gold–gold distance of 2.9931(6) Å and a gold–iodo distance of 3.0999(6) Å, whilst the triflate derivative displays di-coordinated gold centres and a gold–gold distance of 2.9838(5) Å. All the derivatives are intensely photoluminescent in the visible range, with the emission maxima between 480 and 513 nm at 298 K and 459–508 nm at 77 K. The emission energies and the gold–gold distances are not directly related.