Theoretical DFT Investigation of Structure and Electronic Properties of η⁵-Cyclopentadienyl Half-Sandwich Organochalcogenide Complexes

For the first time, an extensive theoretical comparative study of the electronic structure and spectra of the η⁵-cyclopentadienyl half-sandwich [(Cp)(EPh₃)], E = Se, Te) organochalcogenides was carried out using direct space electronic structure calculations within hybrid, meta, and meta-hybrid DFT GGA functionals coupled with double-ζ polarized 6-31G* and correlation-consistent triple-zeta cc-pVTZ-pp basis sets. The absence of covalent bonding between the cyclopentadienyl (Cp) ligands and Te/Se coordination centers was revealed. It was found that the chalcogens are partially positively charged and Cp ligands are partially negatively charged, which directly indicates a visible ionic contribution to Te/Se-Cp chemical bonding. Simulated UV–Vis absorption spectra show that all complexes have a UV-active nature, with a considerable shift in their visible light absorption due to the addition of methyl groups. The highest occupied molecular orbitals exhibit π-bonding between the Te/Se centers and Cp rings, although the majority of the orbital density is localized inside the Cp π-system. The presence of the chalcogen atoms and the extension of π-bonds across the chalcogen-ligand interface make the species promising for advanced photovoltaic and light-emitting applications.