Magnetically induced currents and aromaticity in ligand-stabilized Au and AuPt superatoms

Abstract

Understanding magnetically induced currents (MICs) in aromatic or metallic nanostructures is crucial for interpreting local magnetic shielding and NMR data. Direct measurements of the induced currents have been successful only in a few planar molecules but their indirect effects are seen in NMR shifts of probe nuclei. Here, we have implemented a numerically efficient method to calculate gauge-including MICs in the formalism of auxiliary density functional theory. We analyze the currents in two experimentally synthesized gold-based, hydrogen-containing ligand-stabilized nanoclusters [HAu9(PPh3)8]2+ and [PtHAu8(PPh3)8]+. Both clusters have a similar octet configuration of Au(6s)-derived delocalized “superatomic” electrons. Surprisingly, Pt-doping in gold increases the diatropic response of the superatomic electrons to an external magnetic field and enhances the aromaticity of [PtHAu8(PPh3)8]+. This is manifested by a stronger shielding of the hydrogen proton in the metal core of the cluster as compared to [HAu9(PPh3)8]2+, causing a significant upfield shift in agreement with experimental proton NMR data measured for these two clusters. Our method allows the determination of local magnetic shielding properties for any component in large 3D nanostructures, opening the door for detailed interpretation of complex NMR spectra.

Z-Contrast Enhancement in Au–Pt Nanocatalysts by Correlative X-ray Absorption Spectroscopy and Electron Microscopy: Implications for Composition Determination

“…We have chosen peptide-capped PtAu BNPs for this study based upon their wide range of potential applications. , To fabricate the BNPs in water, a multistep coreduction process was developed to generate the final materials. They were passivated on the surface using the AuBP2 peptide (WALRRSIRRQSY), previously identified with an affinity for Au .…”

1H NMR global diatropicity in copper hydride complexes

“…Therefore, we studied the magnetically induced current density J (1) (r) obtained by the gauge-including magnetically induced currents (GIMIC). 53,54,57 Within the computations a magnetic field in the z-direction B = (0, 0, 1 T) was imposed for both clusters 1 and 2. The magnetically induced current density at J (1) (r) = 0.01 nA T −1 is shown in Fig.…”

“…70 The 1 H chemical shifts for the hydrides were referenced against the 1 H chemical shift of TMS computed at the same level of theory. The magnetically induced current densities were computed employing our recent implementation 53,54 of the electronic structure method for the gauge-including magnetically induced currents (GIMIC) theory. 57 All computations were performed with the quantum chemistry code deMon2k.…”

“…We perform asystematic analysis of the chemical bonding in these clusters, 1 H NMR chemical shifts, dynamic effects on the Cu-μ 3 -H distances, and thermal contributions to the NMR peaks. Finally, we use our recent implementation of gauge-including magnetically induced currents (GIMIC) 53,54 to analyse the diatropic and paratropic currents generated by the external magnetic field in the NMR probe. We observe a global diatropic current around a chain of six Cu atoms that form (111)-like facets but also a highly localized diatropic current around the μ 3 -H hydrides shielding for the nuclei and thus causing an upfield negative shift in the NMR spectrum.…”

Magnetically induced ring currents in naphthalene-fused heteroporphyrinoids

“…To this end, we have derived magnetically induced current densities using the GIMIC method 60,[67][68][69] to elucidate the aromatic nature of the two synthesized novel porphyrinoids, and an analogous compound, in which the naphthalene moiety is replaced with a quinoline. The GIMIC method has been successfully used for assessing the degree of aromaticity in a number of molecules with complex molecular structures, including several porphyrinoids, 24,28,[30][31][32]36,[70][71][72][73][74][75][76][77] which have been recently reviewed. [78][79][80] The current pathways and ringcurrent strengths calculated using GIMIC yield unambiguous pictures of the aromatic character of complex molecules with many annelated molecular rings.…”