Atomically-precise gold nanoclusters have generated tremendous interest in recent years due their physicochemical properties and potential applications in chemical sensing, catalysis, and nanomedicine. Many structurally determined gold nanoclusters with defined elemental compositions have been synthesized and characterized in the recent decades, with phosphine-based ligands used for stabilization.1 One of the peculiar gold nanoclusters is the triphenylphosphine-stabilized nonagold ([Au9(PPh3)8]3+) cluster that exhibits fluxional behavior between two isomers with D2 and C4 cores. The crystal form was structurally determined to be the D2 isomer, whereas the C4 isomer is the dominant species in solutions. Both D2 and C4 isomers are present in water suspensions. In this presentation, we will demonstrate how we determined the D2 & C4 isomeric forms of this nanocluster using spectroscopic techniques and theoretical calculations.2 Likewise, the results of molecular dynamics simulations of the two isomers with solvent molecules show that lateral Au-Au bonds of the D2 isomer tend to be more fluxional than those of C4. Finally, we will reveal the mechanistic insights into how the cluster isomerizes by finding low-lying transition states computationally.