A Molecular Planetarium: Evidence for an Iodide Ligand Orbiting Two Gold(I) Ions in the Luminescent Cation, [Au₂(μ-1,2-Bis(diphenylphosphino)methane)₂I]⁺

Four new crystalline gold(I) complexes, [Au₂(μ-dppm)₂I][Au₂(μ-dppm)₂(μ-I)](AsF₆)₄·4CH₂Cl₂ (<b>1</b>), [Au₂(μ-dppm)₂(μ-I)]I·2CH₂Cl₂ (<b>2</b>), [Au₂(μ-dppm)₂(μ-I)](PF₆)·CH₂Cl₂ (<b>3</b>), and [Au₂(μ-dppm)₂](AsF₆)₂·CH₂Cl₂ (<b>4</b>) where dppm is bis(diphenylphosphino)methane) have been prepared and structurally characterized by single crystal X-ray diffraction and nuclear magnetic resonance spectroscopy (NMR). Yellow crystals of [Au₂(μ-dppm)₂(μ-I)]I·2CH₂Cl₂ (<b>2</b>) and [Au₂(μ-dppm)₂(μ-I)](PF₆)·CH₂Cl₂ (<b>3</b>) have a structure with two three-coordinate gold(I) ions held in close proximity by the dppm and bridging iodide ligands. Crystals of [Au₂(μ-dppm)₂I][Au₂(μ-dppm)₂(μ-I)](AsF₆)₄·4CH₂Cl₂ (<b>1</b>) have two different cations: one similar to complexes <b>2</b> and <b>3</b> and the other cation with a terminal iodide ligand in an unusual arrangement that binds a two-coordinate gold(I) ion to a three-coordinate gold(I) ion through an aurophilic interaction. In contrast, [Au₂(μ-dppm)₂](AsF₆)₂·CH₂Cl₂ (<b>4</b>) has no anion bound and only has the gold ions as two-coordinate centers. Each complex displays luminescence under UV irradiation in the solid and solution states. Remarkably, the NMR spectra of solutions of the iodide complexes (<b>1</b>), (<b>2</b>), and (<b>3</b>) suggest that the iodide ion is bound to the [Au₂(μ-dppm)₂]²⁺ core but is able to circulate around this core.