Insight Into the Stability and Electronic and Optical Properties of N-Heterocyclic Carbene Analogues of Halogen/Phosphine-Protected Au₁₃Superatomic Clusters

Abstract

Atomically-precise gold nanoclusters (AuNCs) belong to a relevant area offering useful templates with tunable properties towards functional nanostructures. In this work, we explored the feasible incorporation of N-heterocyclic carbenes (NHCs), as part of the protecting-ligand shell in AuNCs. Our results based on the substitution of phosphine ligands in experimentally characterized AuNCs by NHCs in various 8-electron superatoms Au 13 and M 4 Au 9 (M = Cu, Ag) indicate similar electronic structure and stability, but somewhat different optical properties. These findings support the feasible obtention of novel targets for explorative synthetic efforts featuring NHC-ligands on medium-sized species based on the recurrent Au 13 icosahedral core. The hypothetical species appear to be interesting templates for building blocks in nanostructured materials with tuned properties, which encourage experimental exploration of ligand-versatility in homo and heterometallic superatomic clusters.

Ligand-Induced Cuboctahedral versus Icosahedral Core Isomerism within Eight-Electron Heterocyclic-Carbene-Protected Gold Nanoclusters

“…The shape of the calculated UV–vis spectrum of [Au 13 (PMePh 2 ) 8 Br 4 ] + is in a good agreement with the available experimental spectra. , The computed lowest absorption energy wavelength (427 nm) is close to the corresponding experimental value (440 nm). The absorption spectrum of its related NHC counterpart, [Au 13 ( i PrIm) 8 Br 4 ] + (ico), exhibits a red-shifted lowest-energy band (518 nm) but a blue-shifted highest-energy band, which is in line with our previous studies . As expected, the [Au 13 ( i PrIm) 8 Br 4 ] + (cubo) isomer shows an intrinsically different UV–vis spectrum.…”

“…The absorption spectrum of its related NHC counterpart, [Au 13 (iPrIm) 8 Br 4 ] + (ico), exhibits a red-shifted lowest-energy band (518 nm) but a blue-shifted highest-energy band, which is in line with our previous studies. 24 As expected, the [Au 13 (iPrIm) 8 Br 4 ] + (cubo) isomer shows an intrinsically different UV−vis spectrum. In comparison to its icosahedral isomer, its lowest-energy band is blue-shifted to 425 nm, which is in agreement with its larger HOMO−LUMO gap.…”

“…It turns out that, within the framework of our general investigations on the stabilization of AuNCs by N-heterocyclic carbenes (NHCs), − we found that some NHCs can, in certain circumstances, stabilize cuboctahedral cluster cores, suggesting rational control of the core structure with respect to the nature of the ligand shell. NHCs have been recently introduced in AuNC chemistry as alternative neutral two-electron ligands of phosphines and appear to favor promising photoemissive properties. − This is why we recently investigated, by means of density functional theory (DFT) calculations (see the Supporting Information for Computational Details), hypothetical NHC analogues of the eight-electron phosphine/halogenide heteroleptic clusters [Au 13 (PR 3 ) n X 12– n ] ( n −7)+ (X = halogen). ,− Interestingly, our calculations show that, at least in the tetrabromide case, the cuboctahedral [Au 13 (NHC) 8 Br 4 ] + species can be stabilized, as described below.…”

N-Heterocyclic carbene derivatives to modify gold superatom characteristics. Tailorable electronic and optical properties of [Au11(PPh3)7LCl2]+ as a cluster from relativistic DFT

“…All optimized singlet ground state structures were confirmed as genuine minima on their potential energy surface using vibrational frequency calculations, as in previous works. 97 Electronic excitation energies were calculated via TD-DFT considering the van Leeuwen–Baerends (LB94) xc-functional as in previous similar studies. 94,98,99…”

Understanding a ligand's effects on intra-cluster and inter-cluster assembly

“…[8][9][10][11][12][13] With the rapid development of thiolate-protected NCs, other types of ligands ( phosphine ligands, alkyne ligands, selenium ligands, carbene ligands, or their combinations) that protect NCs have quickly emerged as new and prominentalternatives. [13][14][15][16][17][18] In previous studies, researchers have explored in-depth the precise structures of nanoclusters and understood the effects of different ligands on their overall properties. For instance, para-, meta-, and ortho-methylbenzenethiols (MBTs) would prefer to generate Au 130 ( p-MBT) 50 , Au 104 (m-MBT) 41 , and Au 40 (o-MBT) 24 , respectively.…”