title: Chasing the Evasive Fe═O Stretch and the Spin State of the Iron(IV)-Oxo Complexes by Photodissociation Spectroscopy.
abstract: We demonstrate the application of infrared photodissocation spectroscopy for determination of the Fe═O stretching frequencies of high-valent iron(IV)-oxo complexes [(L)Fe(O)(X)]2+/+(L = TMC, N4Py, PyTACN, and X = CH3CN, CF3SO3, ClO4, CF3COO, NO3, N3). We show that the values determined by resonance Raman spectroscopy in acetonitrile solutions are on average 9 cm-1red-shifted with respect to unbiased gas-phase values. Furthermore, we show the assignment of the spin state of the complexes based on the vibrational modes of a coordinated anion and compare reactivities of various iron(IV)-oxo complexes generated as dications or monocations (bearing an anionic ligand). The coordinated anions can drastically affect the reactivity of the complex and should be taken into account when comparing reactivities of complexes bearing different ligands. Comparison of reactivities of [(PyTACN)Fe(O)(X)]+generated in different spin states and bearing different anionic ligands X revealed that the nature of anion influences the reactivity more than the spin state. The triflate and perchlorate ligands tend to stabilize the quintet state of [(PyTACN)Fe(O)(X)]+, whereas trifluoroacetate and nitrate stabilize the triplet state of the complex.
authors.affiliation: Department of Organic Chemistry, Faculty of Science, Charles University , Hlavova 2030/8, 12843 Prague 2, Czech Republic.
authors.forename: Erik
authors.initials: E
authors.lastname: Andris
authors.affiliation: Department of Organic Chemistry, Faculty of Science, Charles University , Hlavova 2030/8, 12843 Prague 2, Czech Republic.
authors.forename: Rafael
authors.initials: R
authors.lastname: Navrátil
authors.affiliation: Department of Organic Chemistry, Faculty of Science, Charles University , Hlavova 2030/8, 12843 Prague 2, Czech Republic.
authors.forename: Juraj
authors.initials: J
authors.lastname: Jašík
authors.affiliation: Department of Organic Chemistry, Faculty of Science, Charles University , Hlavova 2030/8, 12843 Prague 2, Czech Republic.
authors.forename: Thibault
authors.initials: T
authors.lastname: Terencio
authors.affiliation: J. Heyrovsky Institute of Physical Chemistry of the CAS , v.v i., Dolejškova 2155/3, 182 23 Prague 8, Czech Republic.
authors.forename: Martin
authors.identifier: 0000-0001-5118-141X
authors.initials: M
authors.lastname: Srnec
authors.affiliation: Departament de Quimica and Institute of Computational Chemistry and Catalysis (IQCC), University of Girona , Campus Montilivi, Girona 17071, Spain.
authors.forename: Miquel
authors.identifier: 0000-0001-6326-8299
authors.initials: M
authors.lastname: Costas
authors.affiliation: Department of Organic Chemistry, Faculty of Science, Charles University , Hlavova 2030/8, 12843 Prague 2, Czech Republic.
authors.forename: Jana
authors.identifier: 0000-0001-5144-0688
authors.initials: J
authors.lastname: Roithová