Abstract
The research projects presented in this dissertation were focused on the physical and spectroscopic characterization of iron(II) complexes of biomedical and catalytic interest. To investigate the compounds of interest, we have employed a large variety of spectroscopic and theoretical techniques, mainly infrared and Mössbauer spectroscopies, augmented by Density Functional Theory (DFT) and ab-initio Complete Active Space (CAS) calculations.We have probed the mechanism of CO-release and the electrochemistry of low-spin iron(II) carbon-monoxide releasing molecules which have a Fe(CO)2(S2CNR2)2 general formula. Using frozen-matrix photolysis techniques we have found that these complexes undergo intramolecular cis- to trans-CO isomerization followed by loss of a CO ligand. We have also determined using cyclic voltammetry and spectroelectrochemistry that the electrochemical behavior of these complexes is ligand-centered, in stark contrast to that of the related homoleptic iron(III) complexes Fe(S2CNR2)3, which exhibit exclusively metal-centered redox events.
We have elucidated the electronic structure of a series of heterobimetallic [FePt] lantern complexes which incorporate a four-fold symmetric, square-planar [FeO4] structural motif. Analogous moieties have been found at the active sites of catalytically active iron-doped zeolites and of unusual square-planar iron(II) complexes supported by non-macrocyclic ligands. Our Mössbauer spectroscopic study has revealed these compounds exhibit an unprecedented variability in their quadrupole splitting values which, for some complexes, show a marked time-dependent change. Additionally, some of these complexes were found to exhibit a large zero field splitting characterized by a positive D value. Utilizing a crystal field approach, we have determined that the observed spectroscopic parameters originate from the spin-orbit coupling of the orbital ground state to two low-lying excited orbital states. Furthermore, the geometries of the iron sites are modulated by the coupling of the pseudo Jahn-Teller interactions at the iron(II) site to the rotation of the pyridine co-ligand.
Lastly, we describe our efforts to characterize a high-spin iron(II) complex featuring redox-active indigo ligands. Our synthetic studies have yielded insight into the complex’s formation and have provided a basis for future catalytic studies. While the structure of the iron bisindigocomplex remains elusive, our Mössbauer studies indicate that this compound likely incorporates either a discrete tetrahedral iron site or an extended, 1 D chain of octahedral units.