Fe(dppe)(η5-C5Me5)-Based Phenylalkynyl Complexes Featuring an NO2 End Group: A Theoretical Analysis

Electronic structures and optical properties of a series of compounds Fe(dppe)(η5-C5Me5){[C≡C(1,4-C6H4)]nNO2} (1–3; n = 1–3, dppe = 1,2-bis(diphenylphosphino)ethane) were investigated with the aid of density functional theory and time-dependent density functional theory computations. The results reveal that the extension of the carbon-rich chain has a moderate influence on the electronic properties of the studied compounds in their ground state, but affects notably their spectroscopic properties, with some unexpected hypsochromic shift of the lower energy absorption bands upon carbon chain lengthening. The appropriate excitations responsible for the low-energy absorption bands involve mainly HOMO–LUMO transitions dominated by important metal-to-ligand charge transfer. A functional including long-range corrections is necessary to reproduce the experimental results.