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

The 1,3,7,9-tetraferrocenylazadipyrromethene (<b>3</b>) and the corresponding 1,3,5,7-tetraferrocene aza-BODIPY (<b>4</b>) 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 <b>3</b> 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 <b>3</b> and <b>4</b>, 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 [<b>3</b>]⁺ and [<b>4</b>]⁺ 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 [<b>3</b>]^<i>n</i>+ and [<b>4</b>]^<i>n</i>+ species (<i>n</i> = 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 <b>3</b> and <b>4</b> as well as predominant spin localization at the ferrocene fragment attached to the α-pyrrolic positions in [<b>3</b>]⁺ and [<b>4</b>]⁺

Tuning Electron-Transfer Properties in 5,10,15,20-Tetra(1′-hexanoylferrocenyl)porphyrins as Prospective Systems for Quantum Cellular Automata and Platforms for Four-Bit Information Storage

Metal-free (<b>1</b>) and zinc (<b>2</b>) 5,10,15,20-tetra­(1′-hexanoylferrocenyl)­porphyrins were prepared using an acid-catalyzed tetramerization reaction between pyrrole and 1′-(1-hexanoyl)­ferrocencarboxaldehyde. New organometallic compounds were characterized by combination of ¹H, ¹³C, and variable-temperature NMR, UV–vis, magnetic circular dichroism, and high-resolution electrospray ionization mass spectrometry methods. The redox properties of <b>1</b> and <b>2</b> were probed by electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation approaches coupled with UV–vis–near-IR and Mössbauer spectroscopy. Electrochemical data recorded in the dichloromethane/TBA­[B­(C₆F₅)₄] system (TBA­[B­(C₆F₅)₄] is a weakly coordinating tetrabutylammonium tetrakis­(pentafluorophenyl)­borate electrolyte) are suggestive of “1e^– + 1e^– + 2e^–” oxidation sequence for four ferrocene groups in <b>1</b> and <b>2</b>, which followed by oxidation process centered at the porphyrin core. The separation between all ferrocene-centered oxidation electrochemical waves is very large (510–660 mV). The nature of mixed-valence [<b>1</b>]^<i>n</i>+ and [<b>2</b>]^<i>n</i>+ (<i>n</i> = 1 or 2) complexes was probed by the spectroelectrochemical and chemical oxidation methods. Analysis of the intervalence charge-transfer band in [<b>1</b>]⁺ and [<b>2</b>]⁺ is suggestive of the Class II (in Robin–Day classification) behavior of all mixed-valence species, which correlate well with Mössbauer data. Density functional theory–polarized continuum model (DFT-PCM) and time-dependent (TD) DFT-PCM methods were applied to correlate redox and optical properties of organometallic complexes <b>1</b> and <b>2</b> with their electronic structures

Preparation, X‑ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron–Zirconium and Iron–Hafnium Porphyrinoclathrochelates

The first hybrid di- and trinuclear iron­(II)–zirconium­(IV) and iron­(II)–hafnium­(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between <i>n</i>-butylboron-triethylantimony-capped or bis­(triethylantimony)-capped iron­(II) clathrochelate precursors and dichlorozirconium­(IV)- or dichlorohafnium­(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx₃((B<i>n</i>-Bu)­(MTPP)) and FeNx₃(MTPP)₂ [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato­(2-); Nx = nioximo­(2-)] were characterized by one-dimensional (¹H and ¹³C­{¹H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV–visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx₃(MTPP)₂ complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures

Preparation, X‑ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron–Zirconium and Iron–Hafnium Porphyrinoclathrochelates

The first hybrid di- and trinuclear iron­(II)–zirconium­(IV) and iron­(II)–hafnium­(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between <i>n</i>-butylboron-triethylantimony-capped or bis­(triethylantimony)-capped iron­(II) clathrochelate precursors and dichlorozirconium­(IV)- or dichlorohafnium­(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx₃((B<i>n</i>-Bu)­(MTPP)) and FeNx₃(MTPP)₂ [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato­(2-); Nx = nioximo­(2-)] were characterized by one-dimensional (¹H and ¹³C­{¹H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV–visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx₃(MTPP)₂ complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures