Electron paramagnetic resonance in positively charged Au25 molecular nanoclusters

Abstract

In this study, we investigated the unpaired electrons and singly occupied molecular orbitals (SOMO) of positively charged Au(25) molecular clusters using solid-state electron paramagnetic resonance (EPR). The EPR powder spectra of the positively charged (Au(25) (+)) and neutral (Au(25) (0)) species of Au(25) are discussed and compared. Our study demonstrates that Au(25) (+) is paramagnetic with a SOMO that is mostly localized about the central gold atom in the core of the molecule and possesses a strong p-type atomic character. The unpaired electron spin is demonstrated to strongly interact with the nuclear spins from other (197)Au nuclei in the core of Au(25) (+) molecules and the hyperfine tensor describing such interaction was extracted from the comparison of the EPR spectra with quantum mechanical simulations assuming an anisotropic structure of the core. Our simulations suggest that the core of Au(25) (+) molecular clusters is more distorted than in the corresponding neutral counterpart. They also confirm previous hypotheses suggesting that the icosahedral core of Au(25) (+) experiences contraction with decreasing temperature.

Jahn–Teller effects in Au25(SR)18

“…We performed density functional theory (DFT) calculations using the GPAW package that implements projector augmented-wave (PAW) method in a real-space grid. 25 Electronic structure, charge distribution, magnetic states and optical absorption of the clusters in all charge states were analyzed. Crystal structure coordinates including the full ligand layer were used as such without structural relaxation to the theoretical minimum.…”

“…There are conflicting reports, however, regarding the nature of the +1 cluster, with two studies concluding diamagnetism and one study concluding paramagnetism. 21 , 23 – 25 …”

Chemically Modified Gold Superatoms and Superatomic Molecules

“…Interestingly, however, the Au 13 core with different charge states, such as Au 13 6+ and Au 13 7+ , can be isolated by electrochemical and/or chemical oxidation because the ligands can act as a capacitive layer. Various properties of Au 13 5+ superatoms, including photoexcited dynamics, photocatalytic, electrocatalytic, catalytic, and magnetic properties, have been studied extensively by taking advantage of the remarkably high stability of [Au 25 (SR) 18 ] − . The intrinsic properties of Au 13 5+ superatoms are not crucially affected by the R moiety, but can be tuned by proper choice of the ligand .…”

Charge Redistribution Effects on the UV–Vis Spectra of Small Ligated Gold Clusters: a Computational Study

“…In ref. 50 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 16 assuming a partial charge of -0.05|e|, while the Au 25 core carries a positive charge of 3.89|e|, as reported in Table 3. Figure 7b shows that, also in this case, the charge depletion from the gold core correlates with a shift of the optical spectrum toward higher energies.…”