DFT insights into the adsorption, sensing, and electronic response of toxic cyanide species XC≡N (X = H, F, Cl, and Br) on coinage metals

The adsorption of highly toxic cyanide-based warfare-agent analogues, XC≡N (X = H, F, Cl, and Br), on coinage metal clusters M₆ (M = Cu, Ag, and Au) was systematically investigated using density functional theory. Geometry optimization, adsorption energy analysis, conceptual DFT descriptors, molecular electrostatic potential maps, density of states, UV–Vis spectra, Raman shifts, and noncovalent interaction analyses were employed to clarify the binding behavior and sensing potential of these metal clusters. The results reveal that adsorption is strongly controlled by the nature of both the metal cluster and the XC≡N substituent. In the gas phase, halogenated cyanides, particularly BrCN, generally show stronger adsorption due to enhanced polarizability, dispersion interactions, and interfacial charge redistribution. In aqueous media, solvent polarization further stabilizes the complexes and can modify the adsorption order, highlighting the important role of environmental effects. Frontier orbital and DOS analyses confirm strong metal-ligand electronic coupling, reduced energy gaps, and improved charge-transfer characteristics after adsorption. UV–Vis simulations show pronounced bathochromic shifts from the deep ultraviolet region to the visible range upon complexation, while Raman spectral changes indicate surface-enhanced Raman scattering behavior. NCI and RDG analyses further confirm that the adsorption process is mainly governed by van der Waals forces, electrostatic interactions, and halogen-dependent polarization effects. The Ag-, Au-, and Cu-based nanoclusters have exceptional reusability and rapid desorption kinetics, as shown by the computed recovery durations, underscoring their potential as highly recyclable sensors. Overall, the findings suggest that Cu₆, Ag₆, and Au₆ clusters, especially toward halogenated XC≡N species, are promising candidates for molecular recognition, optical sensing, and capture of cyanide-based toxic agents.