Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange
Year: 2017
Type: article
Abstract: Three ferric dipyrromethene complexes featuring different ancillary ligands were synthesized by one electron oxidation of ferrous precursors. Four-coordinate iron complexes of the type ( Ar L)FeX 2 [ Ar L = 1,9-(2,4,6-Ph 3 C 6 H 2 ) 2 -5-mesityldipyrromethene] with X = Cl or t BuO were prepared and found to be high-spin ( S = 5 / 2 ), as determined by superconducting quantum interference device magnetometry, electron paramagnetic resonance, and 57 Fe Mössbauer spectroscopy. The ancillary ligand substitution was found to affect both ground state and excited properties of the ferric complexes examined. While each ferric complex displays reversible reduction and oxidation events, each alkoxide for chloride substitution results in a nearly 600 mV cathodic shift of the Fe III/II couple. The oxidation event remains largely unaffected by the ancillary ligand substitution and is likely dipyrrin-centered. While the alkoxide substituted ferric species largely retain the color of their ferrous precursors, characteristic of dipyrrin-based ligand-to-ligand charge transfer (LLCT), the dichloride ferric complex loses the prominent dipyrrin chromophore, taking on a deep green color. Time-dependent density functional theory analyses indicate the weaker-field chloride ligands allow substantial configuration mixing of ligand-to-metal charge transfer into the LLCT bands, giving rise to the color changes observed. Furthermore, the higher degree of covalency between the alkoxide ferric centers is manifest in the observed reactivity. Delocalization of spin density onto the tert -butoxide ligand in ( Ar L)FeCl(O t Bu) is evidenced by hydrogen atom abstraction to yield ( Ar L)FeCl and HO t Bu in the presence of substrates containing weak C–H bonds, whereas the chloride ( Ar L)FeCl 2 analogue does not react under these conditions.
Source: Inorganic Chemistry
Institution: Harvard University
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2609467608