Probing the Formation, Structure, and Reactivity of Zn(II), Ag(I), and Fe(II) Complexes with 2,2′:6′,2″-Terpyridine on Ag Nanoparticles Surfaces by Time Evolution of SERS Spectra, Factor Analysis, and DFT Calculations

The adsorption and surface reactivity of 2,2′:6′,2″-terpyridine (tpy) and its metal (M = Zn²⁺, Fe²⁺, Ag⁺) complexes on Ag nanoparticle surfaces together with the structure of the resulting M_s^X+-tpy surface species and the mechanism of their formation have been investigated. The process was elucidated by time-dependent surface-enhanced Raman scattering (SERS) spectra, their treatment by factor analysis (FA), density functional theory (DFT) calculations of Raman spectra, and comparison of the SERS spectra of the surface species (obtained by FA) with the Raman spectra of their synthetic analogues (characterized by X-ray diffraction). SERS spectral time evolution revealed surface-induced decomposition of the [Zn­(tpy)₂]²⁺ complex and formation of Zn_s²⁺-tpy and Ag_s⁺-tpy surface species, accompanied by a ligand exchange of one tpy ligand for chloride anions on the Zn²⁺ center. The inhibition of Ag_s⁺-tpy surface species formation was achieved by addition of Zn²⁺ cations prior to the addition of the [Zn­(tpy)₂]²⁺ complex. The [Fe­(tpy)₂]²⁺ complex exhibited no surface decomposition and was identical to the Fe_s²⁺-tpy surface species. Additionally, generation of M_s^X+-tpy species on the Ag nanoparticle surfaces by reaction of tpy and M^<i>x</i>+ cations was monitored by SERS and evaluated by FA. Determination of the Zn_s²⁺-tpy and Ag_s⁺-tpy structures was supported by DFT calculations of the Raman spectra of Zn-tpy and Ag-tpy fragments