Probing the electronic structure and Au–C bonding in AuC2nH (n = 4–7) using photoelectron imaging spectroscopy and quantum chemical calculations

We report a combined experimental and theoretical study on the structures and chemical bonding of AuC2nH (n = 4–7) using photoelectron imaging and quantum chemical calculations. All the ground states of anions and neutral AuC2nH have a linear geometry. The electron affinities (EAs) are measured to be 2.063(5), 2.157(5), 2.220(5), and 2.267(5) eV for AuC2nH, n = 4–7, respectively. The photoelectron imaging data of AuC8H− and AuC10H− reveal major vibrational progressions in the Au–C stretching modes. The ground state stretching frequencies of the titled neutral molecules are 226, 193, 177, and 128 cm−1, respectively. By comparing the experimental β value and theoretical molecular orbital analysis, we confirm that the CAM-B3LYP method is more suitable for describing the properties of such unsaturated long chains organogold clusters. The experimental and CAM-B3LYP methods give a big picture of the trend in EAs of AuC2nH. This shows that the EA value becomes larger with an increase in the carbon chain length, and it also shows a slow increment for larger n. The NRT analysis shows that the change of the Au–C bond order is not obvious as the number of carbon atoms increases, and the covalent character dominates the Au–C chemical bonds in these neutral species. The current study provides a wealth of electronic structure information about long-chain AuC2nH− (n = 4–7) and their corresponding neutral counterparts.