title: Observation of the Strong Electronic Coupling in Near-Infrared-Absorbing Tetraferrocene aza-Dipyrromethene and aza-BODIPY with Direct Ferrocene-α- and Ferrocene-β-Pyrrole Bonds: Toward Molecular Machinery with Four-Bit Information Storage Capacity.
abstract: The 1,3,7,9-tetraferrocenylazadipyrromethene (3) and the corresponding 1,3,5,7-tetraferrocene aza-BODIPY (4) were prepared via three and four synthetic steps, respectively, starting from ferrocenecarbaldehyde using the chalcone-type synthetic methodology. The novel tetra-iron compounds have ferrocene groups directly attached to both the α- and the β-pyrrolic positions, and the shortest Fe-Fe distance determined by X-ray crystallography for 3 was found to be ∼6.98 Å. These new compounds were characterized by UV-vis, nuclear magnetic resonance, and high-resolution electrospray ionization mass spectrometry methods, while metal-metal couplings in these systems were probed by electro- and spectroelectrochemistry, chemical oxidations, and Mössbauer spectroscopy. Electrochemical data are suggestive of the well-separated stepwise oxidations of all four ferrocene groups in 3 and 4, while spectroelectrochemical and chemical oxidation experiments allowed for characterization of the mixed-valence forms in the target compounds. Intervalence charge-transfer band analyses indicate that the mixed-valence [3]+and [4]+complexes belong to the weakly coupled class II systems in the Robin-Day classification. This interpretation was further supported by Mössbauer spectroscopy in which two individual doublets for Fe(II) and Fe(III) centers were observed in room-temperature experiments for the mixed-valence [3]n+and [4]n+species (n = 1-3). The electronic structure, redox properties, and UV-vis spectra of new systems were correlated with Density Functional Theory (DFT) and time-dependent DFT calculations (TDDFT), which are suggestive of a ferrocene-centered highest occupied molecular orbital and chromophore-centered lowest unoccupied molecular orbital in 3 and 4 as well as predominant spin localization at the ferrocene fragment attached to the α-pyrrolic positions in [3]+and [4]+.
authors.affiliation: Department of Chemistry & Biochemistry, University of Minnesota Duluth , Duluth, Minnesota 55812, United States.|Department of Chemistry, University of Manitoba , Winnipeg, Manitoba R3T 2N2, Canada.
authors.forename: Yuriy V
authors.initials: YV
authors.lastname: Zatsikha
authors.affiliation: Department of Chemistry & Biochemistry, University of Minnesota Duluth , Duluth, Minnesota 55812, United States.
authors.forename: Cole D
authors.initials: CD
authors.lastname: Holstrom
authors.affiliation: Department of Chemistry, Faculty of Science, Chiang Mai University , Chiang Mai 50200, Thailand.
authors.forename: Kullapa
authors.initials: K
authors.lastname: Chanawanno
authors.affiliation: Department of Chemistry, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Allen J
authors.initials: AJ
authors.lastname: Osinski
authors.affiliation: Department of Chemistry, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Christopher J
authors.identifier: http://orcid.org/0000-0002-0142-5161
authors.initials: CJ
authors.lastname: Ziegler
authors.affiliation: Department of Chemistry & Biochemistry, University of Minnesota Duluth , Duluth, Minnesota 55812, United States.|Department of Chemistry, University of Manitoba , Winnipeg, Manitoba R3T 2N2, Canada.
authors.forename: Victor N
authors.identifier: http://orcid.org/0000-0003-4345-0848
authors.initials: VN
authors.lastname: Nemykin