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Optical spectroscopy of the Au4+ cluster: Resolved vibronic structure indicates an unexpected isomer**
摘要： The knowledge of the geometric and electronic structure of gold clusters and nanoparticles is vital for understanding their catalytic and photochemical properties at the molecular level. Herein, we report the vibronic optical photodissociation spectrum of cold and mass-selected Au4+ clusters measured at a resolution high enough to allow for comparison with Franck-Condon simulations of the excited state transitions based on time-dependent density functional theory calculations. The three vibrational frequencies identified for the lowest-lying optically accessible excited state at 2.17 eV stem from the Y-shaped isomer (C2v) and not from the rhombic isomer (D2h) that is considered to be the ground state structure of Au4+. This study demonstrates that an analysis of low-resolution electronic spectra by calculations of vertical transitions alone is not sufficient for a reliable isomer assignment of such metal clusters.
关键词： gold,UV/Vis spectroscopy,structure elucidation,cluster compounds,electronic structure
更新于2025-09-23 15:23:52
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IR photodissociation spectra of SixH4x-4+ (x?=?4–8): Evidence for Si H Si proton bridges
摘要： Although silane-type cations of the form SixHy+ are thought to play a significant role in plasma chemistry and astrochemistry, their structural and energetic properties are largely unexplored in the size range x ≥ 3. Herein, infrared photodissociation (IRPD) spectra of mass-selected SixHy+ with x = 4–8, specifically SixH4x-4+, are recorded in the Si–H stretch range and analyzed by dispersion-corrected density functional calculations at the B3LYP-D3/aug-cc-pVDZ level. The SixH4x-4+ ions are produced in a SiH4/H2/He plasma molecular beam expansion. The IRPD process leads to the loss of SiH4 ligands, which corresponds to the lowest-energy fragment channel. Spectral analysis of the IRPD spectra reveals that all SixH4x-4+ ions have at least one Si–H–Si bridge. The characteristic fingerprint of these three-center two-electron (3c-2e) bonds is the highly IR active antisymmetric stretch fundamental of the Si–H–Si bridge (νSiHSi) occurring in the 1600–2100 cm?1 range, whose frequency strongly depends on the structural and energetic details of the Si–H–Si bridge. Although the investigated SixH4x-4+ ions can formally be described by the formula Si2H4+(SiH4)x-2, the cluster growth is more complex. The appearance of the νSiHSi bands confirms that all considered SixH4x-4+ ions with x ≤ 5 are formed by polymerization reactions. Larger clusters (x ≥ 6) show evidence for the additional presence of weakly-bonded SiH4 ligands attached to smaller chemically-bonded core ions. Correlations of the properties of the Si–H–Si bridges (bond distances, bond angles, binding energies, Si–H stretch frequencies), which vary between strong symmetric 3c-2e chemical bonds and weak hydrogen bonds, are discussed.
关键词： Silane ions,IR spectroscopy,Structure elucidation,3c-2e bond,Si H Si bridge
更新于2025-09-23 15:23:52
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Single Au Atom Doping of Silver Nanoclusters
摘要： Ag29 nanoclusters capped with lipoic acid (LA) can be doped with Au. The doped clusters show enhanced stability and increased luminescence efficiency. We attribute the higher quantum yield to an increase in the rate of radiative decay. With mass spectrometry, the Au-doped clusters were found to consist predominantly of Au1Ag28(LA)12 3 – . The clusters were characterized using X-ray absorption spectroscopy at the Au L3-edge. Both the extended absorption fine structure (EXAFS) and the near edge structure (XANES) in combination with electronic structure calculations confirm that the Au dopant is preferentially located in the center of the cluster. A useful XANES spectrum can be recorded for lower concentrations, or in shorter time, than the more commonly used EXAFS. This makes XANES a valuable tool for structural characterization.
关键词： x-ray spectroscopy,structure elucidation,doping,Au1Ag28,Ag29,luminescence,bimetallic nanocluster
更新于2025-09-23 15:21:01
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Comparison of 1-Propyl-5H-tetrazole and 1-Azidopropyl-5H-tetrazole as Ligands for Laser Ignitable Energetic Materials
摘要： Laser ignitable explosives are potential candidates in future applications for replacing toxic and very sensitive primary explosives, which are used in current devices. In this study, the literature unknown ligand 1-azidopropyl-5H-tetrazole (APT, 1) was synthesized for the first time and applied in energetic coordination compounds (ECC). The complexes are based on different 3d transition metals (Mn2+, Fe2+, Cu2+, and Zn2+) as well as various oxidizing anions (NO3?, ClO4?, ClO3?) and were tested towards their capability as laser ignitable explosives. Furthermore, analogous complexes based on the literature known ligand 1-propyl-5H-tetrazole (PT, 2) were investigated, for comparing the influence of the additional azide group towards the performance of the ECC. Toxicity measurements using Vibrio fischeri and the decreased sensitivities prove their usability as safer laser ignitable explosive with lower toxicities compared to currently used explosives.
关键词： tetrazole ligands,laser ignition,nitrogen heterocycles,structure elucidation,energetic coordination compounds
更新于2025-09-23 15:19:57
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Synthesis of RE6?xCa1.5xSi11N20O (RE = Yb, Lu; x ≈ 2.2) with Lu6?xCa1.5xSi11N20O:Ce3+ Offering Interesting Spectral Properties ?for Yellow-Emitting Phosphors in 1pcLEDs
摘要： The oxonitridosilicates RE6?xCa1.5xSi11N20O (RE = Yb, Lu; x ≈ 2.2) were synthesized starting from REF3, CaH2, and “Si(NH)2” in a radiofrequency furnace at 1600 or 1400 °C, respectively. The crystal structure was solved and refined from single-crystal X-ray diffraction data of dark red Yb6?xCa1.5xSi11N20O crystals in the trigonal space group P31c (no. 159) with a = 9.8281(10), c = 10.5968(13) ? and Z = 2. The structure represents a filled variant of the Er6Si11N20O structure type, in which the charge difference caused by substitution of trivalent Yb3+ with bivalent Ca2+ is balanced by occupation of an additional third cation site. Synthesis of Lu6?xCa1.5xSi11N20O:Ce3+ resulted in a yellow powder with yellow luminescence. Powder X-ray data were analyzed by Rietveld refinement based on the crystal data obtained from Yb6?xCa1.5xSi11N20O. The Ce3+ doped compound exhibits a broad emission (fwhm ≈ 168 nm / ≈ 5100 cm?1) with a maximum at λem ≈ 565 nm. The emission extends more in the red spectral range compared to YAG:Ce3+, thus making it an interesting phosphor for warm-white single phosphor converted light emitting diodes (1pcLED) with an improved color rendering index.
关键词： Structure elucidation,Solid-state reactions,X-ray diffraction,Luminescence,High-temperature chemistry
更新于2025-09-11 14:15:04
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Aromatic Charge Resonance Interaction Probed by Infrared Spectroscopy
摘要： Charge resonance is a strong attractive intermolecular force in aromatic dimer radical ions. For cations, this stabilization arises from sharing a positive charge between two identical or different molecules (A2 + or AB+) with comparable ionization energies within the π-stacked dimer. Despite its importance, this fundamental interaction has not been characterized at high resolution by spectroscopy of isolated dimers. Herein, we employ vibrational infrared spectroscopy of cold aromatic pyrrole dimer cations to precisely probe the charge distribution by measuring the frequency of the isolated NH stretch mode (νNH). We observe a linear correlation between νNH and the partial charge q on the pyrrole molecule in different environments. Subtle effects of symmetry reduction, such as substitution of functional groups (here pyrrole → N-methylpyrrole) or asymmetric solvation (here by an inert N2 ligand), sensitively shifts the charge distribution toward the moiety with lower ionization energy. This general approach provides a precise experimental probe of the asymmetry of the charge distribution in such aromatic homo- and heterodimer cations.
关键词： charge resonance,IR spectroscopy,cations,structure elucidation,arenes
更新于2025-09-10 09:29:36
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[ACS Symposium Series] Raman Spectroscopy in the Undergraduate Curriculum Volume 1305 || Connecting Organic and Physical Chemistry Students with Raman Spectroscopy
摘要： The profile of Raman spectroscopy may be elevated in the undergraduate chemistry curriculum by intentionally tying together students’ experiences in the organic and physical chemistry laboratories. In this way the valuable role Raman spectroscopy can play in structure elucidation is highlighted. The Committee on Professional Training of the American Chemical Society includes the category of optical molecular spectroscopy (e.g., IR, UV-Vis, Raman, and fluorescence spectroscopies) as an option in the panel of instruments required for certification. To the authors’ knowledge there are no Raman spectroscopy experiments that build directly on the analysis of compounds synthesized by students in a prior course for the intended purpose of scaffolding the curriculum. This chapter highlights the roles Raman spectroscopy may play in the determination of molecular structure when used in conjunction with other, more common techniques. Indeed, direct comparison to infrared spectroscopy holds the potential to reinforce that technique and its applications while introducing the study of Raman spectra. A set of three reaction products from electrophilic aromatic substitution, Diels-Alder, and aldol condensation (this including site-specific deuteration) is explored. All of these reactions are currently part of the organic chemistry curriculum. By combining analyses performed in organic chemistry with new laboratories written for the physical chemistry laboratory the authors hope to impress upon undergraduates the value of Raman spectroscopy in a context that builds on their previous experiences with other molecular spectroscopy methods.
关键词： structure elucidation,undergraduate chemistry curriculum,electrophilic aromatic substitution,Diels-Alder reaction,Raman spectroscopy,infrared spectroscopy,deuteration,physical chemistry,aldol condensation,organic chemistry
更新于2025-09-04 15:30:14