Tuning Copper Active Site Composition in Cu-MOR through Co-Cation Modification for Methane Activation

The industrial implementation of a direct methane-to-methanol process would lead to environmental and economic benefits. Copper zeolites successfully execute this reaction at relatively low temperatures, and mordenite zeolites in particular enable high methanol production. When loaded to a Cu/Al ratio of 0.45, mordenite (Si/Al 5–9) has been shown to host three active sites: two [CuOCu]2+ sites labeled MOR1 and MOR2 and a mononuclear [CuOH]+ site. Also at low copper loadings (Cu/Al < 0.20), mordenite has been demonstrated to activate methane, but its active site has never been reported. Here, we investigate Na+ mordenite with varying copper loadings to better understand copper speciation in mordenite. At low copper loadings, we uncover an unidentified active site (“MOR3”) with a strong overlap with the [CuOH]+ site’s spectroscopic signal. By changing the co-cation, we selectively speciate more MOR3 relative to [CuOH]+, allowing its identification as a [CuOCu]2+ site. Active site identification in heterogeneous catalysts is a frequent problem due to signal overlap. By changing cation composition, we introduce an innovative method for simplifying a material to allow better analysis. This has implications for the study of Cu zeolites for methane-to-methanol and NOx catalysis, but also for studying and tuning heterogeneous catalysts in general

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

Probing Electronic Communications in Heterotrinuclear Fe–Ru–Fe Molecular Wires Formed by Ruthenium(II) Tetraphenylporphyrin and Isocyanoferrocene or 1,1′-Diisocyanoferrocene Ligands

Two new heterotrinuclear Fe–Ru–Fe complexes of ruthenium­(II) tetraphenylporphyrin axially coordinated with a pair of isocyanoferrocene ((FcNC)₂­RuTPP, <b>1</b>) or 1,1′-diisocyanoferrocene (([C₅H₄NC]₂­Fe)₂­RuTPP, <b>2</b>) ligands [Fc = ferrocenyl, TPP = 5,10,15,20-tetraphenylporphyrinato(2−) anion] were synthesized and characterized by UV–vis, magnetic circular dichroism, NMR, and FTIR spectroscopies as well as by electrospray ionization mass spectrometry and single-crystal X-ray diffraction. Isolation of insoluble polymeric {([C₅H₄NC]₂­Fe)­RuTPP}<i>_n</i> molecular wires (<b>3</b>) was also achieved for the first time. The redox properties of the new trinuclear complexes <b>1</b> and <b>2</b> were probed using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation methods and correlated to those of the bis­(<i>tert</i>-butylisocyano)­ruthenium­(II) tetraphenylporphyrin reference compound, (<i>t</i>-BuNC)₂­RuTPP (<b>4</b>). In all cases, the first oxidation process was attributed to the reversible oxidation of the Ru^II center. The second and third reversible oxidation processes in <b>1</b> are separated by ∼100 mV and were assigned to two single-electron Fe^II/Fe^III couples, suggesting a weak long-range iron–iron coupling in this complex. Electrochemical data acquired for <b>2</b> are complicated by the interaction between the axial η¹-1,1′-diisocyanoferrocene ligand and the electrode surface as well as by axial ligand dissociation in solution. Spectroelectrochemical and chemical oxidation methods were used to elucidate the spectroscopic signatures of the [<b>1</b>]^<i>n</i>+, [<b>2</b>]^<i>n</i>+, and [<b>4</b>]^<i>n</i>+ species in solution. DFT and time-dependent DFT calculations aided in correlating the spectroscopic and redox properties of complexes <b>1</b>, <b>2</b>, and <b>4</b> with their electronic structures

Tuning Up an Electronic Structure of the Subphthalocyanine Derivatives toward Electron-Transfer Process in Noncovalent Complexes with C₆₀ and C₇₀ Fullerenes: Experimental and Theoretical Studies

Noncovalent π–π interactions between chloroboron subphthalocyanine (<b>1</b>), 2,3-subnaphthalocyanine (<b>3</b>), 1,4,8,11,15,18-(hexathiophenyl)­subphthalocyanine (<b>4</b>), or 4-<i>tert</i>-butylphenoxyboron subphthalocyanine (<b>2</b>) with C₆₀ and C₇₀ fullerenes were studied by UV–vis and steady-state fluorescence spectroscopy, as well as mass (APCI, ESI, and CSI) spectrometry. Mass spectrometry experiments were suggestive of relatively weak interaction energies between compounds <b>1</b>–<b>4</b> and fullerenes. The formation of a new weak charge-transfer band in the NIR region was observed in solution only for subphthalocyanine <b>4</b> when titrated with C₆₀ and C₇₀ fullerenes. Molecular structures of the subphthalocyanines <b>2</b> and <b>4</b> as well as cocrystallite of <b>4</b> with C₆₀ fullerene (<b>4···C</b>_<b>60</b>) were studied using X-ray crystallography. One of the C₆₀ fullerenes in the crystal structure of <b>4···C</b>_<b>60</b> was found in the concave region between two subphthalocyanine cores, while the other three fullerenes are aligned above individual isoindole fragments of the aromatic subphthalocyanine. The excited-state dynamics in noncovalent assemblies were studied by transient absorption spectroscopy. The time-resolved photophysics data suggest that only electron-rich subphthalocyanine <b>4</b> can facilitate an electron-transfer to C₆₀ or C₇₀ fullerenes, while no electron-transfer from the photoexcited receptors <b>1</b>–<b>3</b> to fullerenes was observed in UV–vis and transient spectroscopy experiments. DFT calculations using the CAM-B3LYP exchange-correlation functional and the 6-31+G­(d) basis set allowed an estimation of interaction energies for the noncovalent 1:1 and 1:2 (fullerene:subphthalocyanine) complexes. Theoretical data suggest that the weak (∼3.5–10.5 kcal/mol) van der Waals-type interaction energies tend to increase with an increase of the electron density at the subphthalocyanine core with compound <b>4</b> being the best platform for noncovalent interactions with fullerenes. DFT calculations also indicate that 1:2 (fullerene:subphthalocyanine) noncovalent complexes are more stable than the corresponding 1:1 assemblies

Initial Report on Molecular and Electronic Structure of Spherical Multiferrocenyl/tin(IV) (Hydr)oxide [(FcSn)₁₂O₁₄(OH)₆]X₂ Clusters

Two spherical organic–inorganic ferrocene-tin (hydr)­oxide clusters of general formula [(FcSn)₁₂O₁₄­(OH)₆]­X₂ (Fc = ferrocenyl, X = nitroso-dicyanmethanide, DCO^– and benzoylcyanoxime, PCO^– anions) were prepared by the direct hydrolysis of Fc₂SnCl₂ or FcSnCl₃ precursors in the presence of light- and thermally stable Ag­(DCO) or Ag­(PCO) salts. Molecular structures of FcSnCl₃Py₂ (<b>1</b>), Fc₂SnCl₂Py₂ (<b>2</b>), [(FcSn)₁₂O₁₄­(OH)₆]­(DCO)₂ (<b>3</b>), and [(FcSn)₁₂O₁₄­(OH)₆]­(PCO)₂ (<b>4</b>) were investigated by X-ray crystallography. Density function theory (DFT) and time-dependent density functional theory (TDDFT) calculations were conducted on FcSnCl₃Py₂, Fc₂SnCl₂Py₂, and [(FcSn)₁₂O₁₄­(OH)₆]²⁺ compounds in order to elaborate electronic structures and assign transitions in UV–vis spectra of these systems. The DFT and TDDFT calculations suggest that the organometallic substituents in the [(FcSn)₁₂O₁₄­(OH)₆]²⁺ core are rather isolated from each other

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