Size Effect on Aurophilic Interaction in Gold-Chloride Cluster Anions of Au n Cl n+1 - (2 ≤ n ≤ 7)

Structures and growth pathways of AunCln+3- (n ≤ 7) cluster anions

Gold chloride clusters play an important role in catalysis and materials chemistry. Due to the diversity of their species and isomers, there is still a dearth of structural studies at the molecular level. In this work, anions of AunCln+3 - and AunCln+5 - (n = 2-4) clusters were obtained by laser desorption/ionization mass spectrometry (LDI MS), and the most stable isomers of AunCln+3 - were determined after a thorough search and optimization at the TPSSh/aug-cc-pVTZ/ECP60MDF level. The results indicate that all isomers with the lowest energy have a planar zigzag skeleton. In each species, there is one Au(III) atom at the edge connected with four Cl atoms, which sets it from the other Au(I) atoms. Four growth pathways for AunCln+3 - (n = 2-7) clusters are proposed (labelled R1, R2, R3 and R4). They are all associated with an aurophilic contact and are exothermic. The binding energies tend to stabilize at ∼ -41 kcal/mol when the size of the cluster increases in all pathways. The pathway R1, which connects all the most stable isomers of the respective clusters, is characterized by cluster growth due to aurophilic interactions at the terminal atom of Au(I) in the zigzag chains. In the pathway of R4 involving Au-Au bonding in its initial structures (n ≤ 3), the distance between intermediate gold atoms grows with cluster size, ultimately resulting in the transfer of the intermediate Au-Au bonding into aurophilic interaction. The size effect on the structure and aurophilic interactions of these clusters will be better understood based on these discoveries, potentially providing new insights into the active but elusive chemical species involved in the corresponding catalytic reactions or nanoparticle synthesis processes.

Bond-bending isomerism and metallophilicity in metal-halogen anions (Cu,Ag,Au)2X3 -, X = F, Cl, Br, I, At

In the framework of DFT (ABINIT package), we have performed atomic relaxations on the (Cu,Ag,Au)₂X₃ ^-, X = F, Cl, Br, I, At anion series. Opposite to linear (MX₂)^- anions, all (M₂X₃)^- systems are triangular (C _2v symmetry). According to the system, we classified these anions in three categories according to the relative strength of electronegativity, chemical hardness, metallophilicity and van der Waals interaction. We found two bond-bending isomers: (Au₂I₃)^- and (Au₂At₃)^-.

The Covalent AuI-AuI Bond in (AuF)n (n = 2∼4): A Perspective to Understand the Closed-Shell AuI···AuI Interaction

The nature of closed-shell Au^I···Au^I attraction is still a conundrum in theoretical chemistry. However, for Au₂F₂ with a zigzag conformation, the d¹⁰-d¹⁰ closed-shell interaction between the AuF monomers is demonstrated as a coordinate covalent bond. Chemical bonding analysis reveals that the strong Au^I···Au^I attraction is caused by the participation of the extraordinary active 5d orbital of Au. Based on our study, one of the 5d orbitals of the Au atom is activated to hybridize with its 6s and 6p orbitals to form hybridized dsp² orbitals, where each Au atom is both an electron donor (Lewis base) and acceptor (Lewis Acid) in dimerization. Actually, the closed-shell Au^I···Au^I interaction in the zigzag conformation of Au₂X₂ (X = F, Cl, Br, I, or NH₂) is covalent. Our results provide a rather simple but clear-cut example, where mysterious Au^I···Au^I attractions can be possibly explained by the covalent bond theory.

Gas-phase generation of dinuclear Au(I)-Au(II) complexes by laser desorption ionization mass spectrometry

Alkali metal chloroaurates(III) were analysed by laser desorption ionization mass spectrometry. Among a number of generated gas-phase ionic clusters, the unusual ions [MAu₂Cl₅]^- (were M stands for Na, K, Rb, Cs) were detected. The spectra of metastable ions and quantum mechanics calculations show the presence of unprecedented Au(I)-Au(II) interactions in the clusters.

Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions

Excimers and exciplexes are defined as assemblies of atoms or molecules A/A' where interatomic/intermolecular bonding appears only in excited states such as [A2 ]* (for excimers) and [AA']* (for exciplexes). Their formation has become widely known because of their role in gas-phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration AuI (5d10 )) through aurophilic contacts. In the corresponding excimers, a new type of Au⋅⋅⋅Au bonding arises, with bond energies and lengths approaching those of ground-state Au-Au bonds between metal atoms in the Au0 (5d10 6s1 ) and AuII (5d9 ) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis.

Reaction of chloroauric acid with histidine in microdroplets yields a catalytic Au-(His)2 complex

An aqueous solution containing histidine (His, 100 μM) and chloroauric acid (HAuCl4, 10 μM) is electrosprayed (-4.5 kV) from a capillary (50 μm in diameter) with N2 nebulizing gas (120 psi). The resulting microdroplets entered a mass spectrometer with a 2 cm flight path. The mass spectrum recorded in negative ion mode showed several peaks including the Au5 nanocluster with the major one being [Au + 2His-2H]-, which is a catalytically active species. The reaction time was less 1 ms, and the yield of [Au + 2His-2H]- was 76%. In contrast, the bulk reaction for the same concentration run at room temperature for 2 h did not produce this species but instead formed Au10 nanocluster. When a solution of water and acetonitrile (1 : 1) containing indoline (100 mM) and the phenylacetylene (200 mM) as well as histidine and chloroauric acid at the same concentrations as above was electrosprayed, the mass spectrum showed the formation of the intermediate [Au + 2His + phenylacetylene + H]+. Upon collecting the microdroplets, the 4-methyl-4,6-diphenyl-1,2-dihydro-4H-pyrrolo[3,2,1-ij] quinolone product was observed by 1H nuclear magnetic resonance and liquid chromatography with a yield of 44%. The microdroplet synthesis using the Au-(His)2 complex as a catalyst was scaled up using room-temperature ultrasonic nebulization to produce the product at the rate of 35 mg min-1, which is semi-preparative and demonstrates the promise of using microdroplet reactions for chemical synthesis.

Greatly Enhanced Electron Affinities of Au2n Cl Clusters (n = 1-4): Effects of Chlorine Doping

Au2n Cl- (n = 1-4) clusters are investigated by both laser ablation mass spectrometry and theoretical calculations. It is interesting to find that the electron affinities of neutral Au2n Cl (n = 1-4) clusters are much larger than those of corresponding pure Au2n clusters. Among them, the electron affinity of Au2Cl is 4.02 eV, which can be defined as a very unique superhalogen that is quite different from classical ones of M n X m (M = metal, X = halogen, and n < m). Natural bond orbital and highest occupied molecular orbital analyses indicate that the extra electron is predominantly delocalized over the positively charged metal moiety in these anionic Au2n Cl- clusters, which is the main reason for the large electron affinities of the corresponding neutral species.