A Surfaced-Enhanced Raman Spectroscopy and Density Functional Theory Study of [Au(CN)₂]⁻/[Au(CN)₄]⁻ Adsorbed on Gold Nanoparticles

Abstract

Surface-enhanced Raman spectroscopy (SERS) can be used to study chemical reactions on metal surfaces. Its detection limit makes it possible to observe long-lived intermediates and conformational changes to reactants and products. However, the interaction between the surface and the adsorbate makes interpretation of SERS spectra difficult. A case in point is provided by our studies of gold nanoparticles exposed to aqueous cyanide solution. These systems are characterized by time-dependent SERS spectra, suggesting either conformational or chemical changes to gold adsorbed cyanide species. Though there has been conjecture as to the nature of the process responsible for the evolving spectra, there is no definitive answer. Herein, we report the results of first-principles studies that, when combined with the SERS data, suggest that the observed shift of the SERS signals is attributable to the transformation of dicyanoaurate ions ([Au(CN) 2 ] À ) to tetracyanoaurate ions ([Au(CN) 4 ] À ) adsorbed to the metal. In the former case, we argue that the C ∞ axis of the ion is oriented parallel to the surface, and in the latter, the 4-fold axis is normal to the gold (111) surface. Further, the [Au(CN) 4 ] À complex is slightly distorted from its D 4h symmetry to enhance surface bonding.

Formation of cyanide compounds during preparation of gold surfaces evidenced by surface‐enhanced Raman spectroscopy

“…It appears clearly that the molecule remains linear when it is free whereas it is bended when it bends when interacting with the gold surface. This point has already been reported and is confirmed by our calculations. In this study, Jacobs et al have also reported the transformation of dicyanoaurate ions to tetracyanoaurate ions Au(CN) 4 − .…”

“…These various compounds with nitrogen atoms can react with the gold surface to form specific molecules. It has already been shown that the CN functional group can react with gold and the SERS signature of cyanide compounds has already been extensively studied, in particular the dicyanoaurate Au(CN) 2 − molecules . In Figure , we compare the DFT calculations of this molecule with our experimental Raman measurements.…”

Radical-Involved Photosynthesis of AuCN Oligomers from Au Nanoparticles and Acetonitrile

“…To date, seldom reports contain data for the low-frequency region below 200 cm −1 for AuCN and its derivatives. 7 The new strong mode displayed here is possibly attributed to the AuAu stretch vibrational frequency, ν(AuAu), due to the 5dσ*− 6pσ electronic transition. 23 The other three neighboring signals at 196, 242, and 312 cm −1 could thus be designated as 2ν(Au Au), 3ν(AuAu), and 4ν(AuAu), respectively.…”

New Understanding on an Old Compound: Insights on the Origin of Chain Sequence Defects and Their Impact on the Electronic Structure of AuCN

“…[7] In ordered AuCN, the gold atom is linked at C, and N ends. [8] Gold cyanide, AuCN, has found application in catalysis, [4,9] sensors, [10] adsorption, [11] SERS (surface-enhanced Raman spectroscopy), [12] and photoluminescence. [13] The understanding of the crystal structure of that solid has been the subject of progressive elucidation for about two decades.…”