Jahn–Teller effects in Au25(SR)18† †Electronic supplementary information (ESI) available: The supplemental information contains additional details about the syntheses and characterization of these compounds. It includes SQUID magnetometry, electrochemical methods, X-ray crystallography information, 

Jahn–Teller distortions are observed in Au25(SR)18 by single crystal X-ray crystallography. SQUID magnetometry, DFT theory, and linear optical spectroscopy corroborate the finding.

This product can also be made through bulk electrolysis in a solution of 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF 6 ) in DCM at a potential of 20 mV vs SCE.
[Au 25 (PET) 18 ] + [PF 6 ] -: Au 25 (PET) 18 + was synthesized by bulk electrolysis from the two times crystallized Au 25 (PET) 18 -. Au 25 (PET) 18was dissolved in a solution containing 0.1M TBAPF 6 in DCM. Bulk electrolysis was preformed at a constant potential in a three-compartment cell at 300 mV vs SCE. Immediately after the bulk electrolysis was complete, the solution was prepared for crystallization, as this compound appears to be unstable in solution for short periods of time. Ethanol was added to the DCM solution used in bulk electrolysis until a precipitate formed. This was than centrifuged and the solution was decanted. This was repeated until the precipitate appears to contain Au 25 (PET) 18 +1 , as judged by UV/Vis. Once this Au 25 (PET) 18 +1 is sufficiently pure the solution will appear green instead of yellow or orange. At this point the Au 25 (PET) 18 +1 was put into a freezer at -20 °C with no insulation.

Electrochemical methods
Electrochemistry was preformed using a BAS 100 B potentiostat. All electrochemical techniques were preformed in a DCM solution containing 0.1M TBAPF 6 using a standard calomel electrode. Cyclic voltammetry, differential potential voltammetry, and square wave voltammetry were performed using a glassy carbon electrode. Bulk electrolysis was performed using a platinum wire for both the working and counter electrode. 85.5 mg, 96.3 mg and 23.6 mg of crystalline Au 25 (PET) 18 in the -1, 0 and +1 charge state, respectively, were powdered and loaded into a gel capsule and placed into a straw. These samples were than measured using a DC head. Temperature dependent susceptibility measurements were made using a magnetic field of 1000 Oe.

Additional Crystal Packing Analysis of Au 25 (PET) 18 +1
The DCM-PF 6 -PF 6 -DCM complex is composed of a coordinating DCM solvent molecule to two fluoride atoms of the PF 6  anion via CHF (2.394 Å) intermolecular interactions ( Figure S8). The PF 6  anion then coordinates to the second PF 6  anion imposed by the P-1 symmetry element via two FF (2.681 Å) intermolecular halidehalide interactions, which seems to be quite typical interaction of PF 6  anions in close proximity in the crystal lattice. 4 Due to the P-1 symmetry of the structure, only the interactions of the DCM-PF 6 complex have been considered in the following. The DCM-PF 6 complex is surrounded by 3 neighboring Au 25 clusters (or 6 when considering full symmetry) and intermolecular interactions are formed to the closest PET ligands ( Figure S7). PET1 and PET2 ligands from one Au 25 cluster coordinate to the DCM solvent molecule via ArHCl (2.621 Å) interactions. PET3' ligand of a second neighboring Au 25 cluster forms ArHCl (2.941 Å) and ArHF (2.590 Å) interactions to both the DCM solvent and the PF 6  anion in a similar manner to PET1'' and PET9'' ligands of the third neighboring Au 25 cluster that likewise form CHF (2.596 Å) and ArHF (2.602 Å) interactions but only to the PF 6  anion. The structure contains numerous organized packing interactions, which are most likely due to the coordinating solvent and anion in the crystal lattice that allow the formation of the organized and directional weak intercluster interactions to be formed instead of mere closest packing of the Au 25 clusters.   Figure S8. Role of the DCM-PF 6 -PF 6 -DCM complex in the crystal packing of Au 25 (PET) 18 +1 : a) Intermolecular CH-halide and halide-halide interactions between the DCM solvent molecule and PF 6  anions and b) space occupied by the DCM-PF 6 -PF 6 -DCM complex in the crystal lattice.  Table S6. Bader charges of the atomic layers (in |e|) for Au 25 (PET) 18 q cluster with different charge states q = -1, 0, +1. Figure S10. Solutions of Au 25 (PET) 18 in the +1(left), 0 (middle) and -1 (right) charge states in dichloromethane.

X-Ray crystallography
X-ray diffraction data from crystals of Au 25 (PET) 18 0 and Au 25 (PET) 18 +1 were recorded on a Bruker Nonius SMART CCD diffractometer employing MoK  radiation (graphite monochromator). Selected details related to the crystallographic experiment are listed in Table S2. Unit cell parameters were obtained from a leastsquares fit to the angular coordinates of all reflections, and intensities were integrated from a series of frames (0.3º ω rotation) covering more than a hemisphere of reciprocal space. Absorption and other corrections were applied by using SADABS. 2 The structure was solved by using direct methods and refined (on F 2 , using all data) by a full-matrix, weighted least-squares process. All non-hydrogen atoms were refined by using anisotropic displacement parameters. Hydrogen atoms were placed in idealized positions and refined by using a riding model. Standard Bruker Nonius control (SMART) and integration (SAINT) software was employed, and Bruker Nonius SHELXTL 3 software was used for structure solution, refinement, and graphics.
Definitions of R 1 and wR2.