Precise Fingerprint Determination of Vibrational Infrared Spectra in a Series of Co(II) Clathrochelates through Experimental and Theoretical Analyses

The energetic demands of modern society for clean energy vectors, such as H2, have caused a surge in research associated with homogeneous and immobilized electrocatalysts that may replace Pt. In particular, clathrochelates have shown excellent electrocatalytic properties for the hydrogen evolution reaction (HER). However, the actual mechanism for the HER catalyzed by these d-metal complexes remains an open debate, which may be addressed via Operando spectroelectrochemistry. The prediction of electrochemical properties via density functional theory (DFT) needs access to thermodynamic functions, which are only available after Hessian calculations. Unfortunately, there is a notable lack in the current literature regarding the precise evaluation of vibrational spectra of such complexes, given their structural complexity and the associated tangled IR spectra. In this work, we have performed a detailed theoretical and experimental analysis in a family of Co-(II) clathrochelates, in order to establish univocally their IR pattern, and also the calculation methodology that is adequate for such predictions. In summary, we have observed the presence of multiple common bands shared by this clathrochelate family, using the B3LYP functional, the LANL2DZ basis, and effective core potentials (ECP) for heavy atoms. The most important issue addressed in this article was therefore related to the detailed assignment of the fingerprint associated with cobalt-(II) clathrochelates, which is a challenging endeavor due to the crowded nature of their spectra.