[Au4(dppb)3]2+ - A Planar Gold Cluster with Bright Excitation Wavelength Dependent Emission.

The reaction of dppb(AuCl)2 and InCl gives the [Au4(dppb)3]2+ cluster where the four gold atoms are arranged in a deltoid. This contrasts all known [Au4]2+ clusters which exclusively form tetrahedral structures. Single crystals of the title compound luminesce with a high quantum yield in the near infrared at room temperature. The excitation wavelength dictates the emission wavelength which ranges from 680 to 918 nm at 77 K. Comprehensive studies of the excitation-dependent emission and luminescence lifetimes in both polycrystalline and single-crystalline samples provide a unique and detailed optical profile of the cluster, uncovering distinct photophysical behavior central to its emissive properties.