The Grotthuss mechanism explains the anomalously high proton mobility in water as a sequence of proton transfers along a hydrogen-bonded (H-bonded) network. However, the vibrational spectroscopic ...signatures of this process are masked by the diffuse nature of the key bands in bulk water. Here we report how the much simpler vibrational spectra of cold, composition-selected heavy water clusters, D⁺(D₂O)n, can be exploited to capture clear markers that encode the collective reaction coordinate along the proton-transfer event. By complexing the solvated hydronium "Eigen" cluster D₃O⁺(D₂O)₃ with increasingly strong H-bond acceptor molecules (D₂, N₂, CO, and D₂O), we are able to track the frequency of every O-D stretch vibration in the complex as the transferring hydron is incrementally pulled from the central hydronium to a neighboring water molecule.
Gas-phase infrared (IR) spectra of larger protonated polycyclic aromatic hydrocarbon molecules, H{sup +}PAH, have been recorded for the first time. The ions are generated by electrospray ionization ...and spectroscopically assayed by IR multiple-photon dissociation (IRMPD) spectroscopy in a Fourier transform ion cyclotron resonance mass spectrometer using a free electron laser. IRMPD spectra of protonated anthracene, tetracene, pentacene, and coronene are presented and compared to calculated IR spectra. Comparison of the laboratory IR spectra to an astronomical spectrum of the unidentified IR emission (UIR) bands obtained in a highly ionized region of the interstellar medium provides for the first time compelling spectroscopic support for the recent hypothesis that H{sup +}PAHs contribute as carriers of the UIR bands.
We report experimental vibrational action spectra (210–2200 cm–1) and calculated IR spectra, using recent ab initio potential energy and dipole moment surfaces, of H7O3 + and H9O4 +. We focus on ...prominent far-IR bands, which postharmonic analyses show, arise from two types of intermolecular motions, i.e., hydrogen bond stretching and terminal water wagging modes, that are similar in both clusters. The good agreement between experiment and theory further validates the accuracy of the potential and dipole moment surfaces, which was used in a recent theoretical study that concluded that infrared photodissociation spectra of the cold clusters correspond to the Eigen isomer. The comparison between theory and experiment adds further confirmation of the need of postharmonic analysis for these clusters.
We use cryogenic ion trap vibrational spectroscopy to study the structure of the protonated water pentamer, H
(H
O)
, and its fully deuterated isotopologue, D
(D
O)
, over nearly the complete ...infrared spectral range (220-4000 cm
) in combination with harmonic and anharmonic electronic structure calculations as well as RRKM modelling. Isomer-selective IR-IR double-resonance measurements on the H
(H
O)
isotopologue establish that the spectrum is due to a single constitutional isomer, thus discounting the recent analysis of the band pattern in the context of two isomers based on AIMD simulations 〈W. Kulig and N. Agmon, Phys. Chem. Chem. Phys., 2014, 16, 4933-4941〉. The evolution of the persistent bands in the D
(D
O)
cluster allows the assignment of the fundamentals in the spectra of both isotopologues, and the simpler pattern displayed by the heavier isotopologue is consistent with the calculated spectrum for the branched, Eigen-based structure originally proposed 〈J.-C. Jiang, et al., J. Am. Chem. Soc., 2000, 122, 1398-1410〉. This pattern persists in the vibrational spectra of H
(H
O)
in the temperature range from 13 K up to 250 K. The present study also underscores the importance of considering nuclear quantum effects in predicting the kinetic stability of these isomers at low temperatures.
A magnesium complex incorporating a novel metal–CO2 binding motif is spectroscopically identified. Here we show with the help of infrared photodissociation spectroscopy that the complex exists solely ...in the ClMg(η2‐O2C)− form. This bidentate double oxygen metal–CO2 coordination has previously not been observed in neutral nor in charged unimetallic complexes. The antisymmetric CO2 stretching mode in ClMg(η2‐O2C)− is found at 1128 cm−1, which is considerably redshifted from the corresponding mode in bare CO2 at 2349 cm−1, suggesting that the CO2 moiety has a considerable negative charge (∼1.8 e−). We also employed electronic structure calculations and kinetic analysis to support the interpretation of the experimental results.
Bidentate coordination of CO2: An anionic complex of MgCl− and CO2, ClMgCO2−, is formed upon electrospray ionization followed by collision‐induced dissociation. With the help of infrared photodissociation spectroscopy it is shown that the complex exists solely in the double oxygen‐bound ClMg(η2‐O2C)− form, a type of CO2 coordination not previously seen in unimetallic complexes.
Significance Understanding the mechanics underlying the diffuse OH stretching spectrum of water is a grand challenge for contemporary physical chemistry. Water clusters play an increasingly important ...role in this endeavor, as they allow one to freeze and isolate the spectral behavior of relatively large assemblies with well-defined network morphologies. We exploit recently developed, hybrid instruments that integrate laser spectroscopy with cryogenic ion trap mass spectrometry to capture the H ₃O ⁺ and Cs ⁺ ions in cage structures formed by 20 water molecules. Their infrared spectra reveal a pattern of distinct transitions that is unprecedented for water networks in this size range. Theoretical analysis of these patterns then reveals the intramolecular distortions associated with water molecules at various sites in the 3D cages.
Theoretical models of proton hydration with tens of water molecules indicate that the excess proton is embedded on the surface of clathrate-like cage structures with one or two water molecules in the interior. The evidence for these structures has been indirect, however, because the experimental spectra in the critical H-bonding region of the OH stretching vibrations have been too diffuse to provide band patterns that distinguish between candidate structures predicted theoretically. Here we exploit the slow cooling afforded by cryogenic ion trapping, along with isotopic substitution, to quench water clusters attached to the H ₃O ⁺ and Cs ⁺ ions into structures that yield well-resolved vibrational bands over the entire 215- to 3,800-cm ⁻¹ range. The magic H ₃O ⁺(H ₂O) ₂₀ cluster yields particularly clear spectral signatures that can, with the aid of ab initio predictions, be traced to specific classes of network sites in the predicted pentagonal dodecahedron H-bonded cage with the hydronium ion residing on the surface.
Mass spectrometry frequently reveals the existence of transient gas phase ions that have not been synthesized in solution or in bulk. These elusive ions are, therefore, often considered to be ...primarily of analytical value in fundamental gas phase studies. Here, we provide proof-of-concept that the products of ion-molecule reactions in mass spectrometers may be collected on surfaces to generate condensed matter and thus serve as building blocks to synthesize new compounds. The highly reactive fragment anion B12Br11- was generated in a mass spectrometer and converted to B12Br11N2- in the presence of molecular nitrogen followed by its mass-selection and soft-landing on surfaces. The molecular structure of B12Br11N2-, which has not been synthetically obtained before, was confirmed by conventional methods of molecular analysis, including nuclear magnetic resonance and infrared spectroscopy. The B12Br11N2- ion is stable on surfaces and in solution at room temperature, but thermal annealing induces elimination of N2 and provides access to the highly reactive intermediate B12Br11- in the condensed phase, which can be further used as a reagent, for example, for electrophilic aromatic substitutions. Thus, isolation of B12Br11N2- expands the repertoire of the available diazo ions that can be employed as versatile intermediates in various chemical transformations.
Fragment ions are well recognized as elusive species in mass spectrometry, typically employed for analytical purposes. In their Communication (e202308600), Jonas Warneke et al. demonstrate that the ...reaction products of fragment ions formed in the gas phase can be “harvested” from a preparative mass spectrometer to become “building blocks” in chemical synthesis.
Transition metal (TM) complexes are widely used in catalysis, photochemical energy conversion, and sensing. Understanding factors that affect ligand loss from TM complexes at interfaces is important ...both for generating catalytically-active undercoordinated TM complexes and for controlling the degradation pathways of photosensitizers and photoredox catalysts. Herein, we demonstrate that well-defined TM complexes prepared on surfaces using ion soft landing undergo substantial structural rearrangements resulting in ligand loss and formation of both stable and reactive undercoordinated species. We employ nickel bipyridine (Ni-bpy) cations as a model system and explore their structural reorganization on surfaces using a combination of experimental and computational approaches. The controlled preparation of surface layers by mass-selected deposition of Ni(bpy)
3
2+
cations provides insights into the chemical reactivity of these species on surfaces. Both surface characterization using mass spectrometry and electronic structure calculations using density functional theory (DFT) indicate that Ni(bpy)
3
2+
undergoes a substantial geometry distortion on surfaces in comparison with its gas-phase structure. This distortion reduces the ligand binding energy and facilitates the formation of the undercoordinated Ni(bpy)
2
2+
. Additionally, charge reduction by the soft landed Ni(bpy)
3
2+
facilitates ligand loss. We observe that ligand loss is inhibited by co-depositing Ni(bpy)
3
2+
with a stable anion such as
closo
-dodecaborate dianion, B
12
F
12
2−
. The strong electrostatic interaction between Ni(bpy)
3
2+
and B
12
F
12
2−
diminishes the distortion of the cation due to interactions with the surface. This interaction stabilizes the soft landed cation by reducing the extent of charge reduction and its structural reorganization. Overall, this study shows the intricate interplay of charge state, ion surface interactions, and stabilization by counterions on the structure and reactivity of metal complexes on surfaces. The combined experimental and computational approach used in this study offers detailed insights into factors that affect the integrity and stability of active species relevant to energy production and catalysis.
Ni(bpy)
3
2+
soft landed on surfaces dissociates spontaneously. Codeposition of stable anions with cations enables preservation of the structure of Ni(bpy)
3
2+
.
Transition metal (TM) complexes are widely used in catalysis, photochemical energy conversion, and sensing. Understanding factors that affect ligand loss from TM complexes at interfaces is important ...both for generating catalytically-active undercoordinated TM complexes and for controlling the degradation pathways of photosensitizers and photoredox catalysts. Herein, we demonstrate that well-defined TM complexes prepared on surfaces using ion soft landing undergo substantial structural rearrangements resulting in ligand loss and formation of both stable and reactive undercoordinated species. We employ nickel bipyridine (Ni-bpy) cations as a model system and explore their structural reorganization on surfaces using a combination of experimental and computational approaches. The controlled preparation of surface layers by mass-selected deposition of Ni(bpy)32+ cations provides insights into the chemical reactivity of these species on surfaces. Both surface characterization using mass spectrometry and electronic structure calculations using density functional theory (DFT) indicate that Ni(bpy)32+ undergoes a substantial geometry distortion on surfaces in comparison with its gas-phase structure. This distortion reduces the ligand binding energy and facilitates the formation of the undercoordinated Ni(bpy)22+. Additionally, charge reduction by the soft landed Ni(bpy)32+ facilitates ligand loss. We observe that ligand loss is inhibited by co-depositing Ni(bpy)32+ with a stable anion such as closo-dodecaborate dianion, B12F122-. The strong electrostatic interaction between Ni(bpy)32+ and B12F122- diminishes the distortion of the cation due to interactions with the surface. This interaction stabilizes the soft landed cation by reducing the extent of charge reduction and its structural reorganization. Overall, this study shows the intricate interplay of charge state, ion surface interactions, and stabilization by counterions on the structure and reactivity of metal complexes on surfaces. The combined experimental and computational approach used in this study offers detailed insights into factors that affect the integrity and stability of active species relevant to energy production and catalysis.Transition metal (TM) complexes are widely used in catalysis, photochemical energy conversion, and sensing. Understanding factors that affect ligand loss from TM complexes at interfaces is important both for generating catalytically-active undercoordinated TM complexes and for controlling the degradation pathways of photosensitizers and photoredox catalysts. Herein, we demonstrate that well-defined TM complexes prepared on surfaces using ion soft landing undergo substantial structural rearrangements resulting in ligand loss and formation of both stable and reactive undercoordinated species. We employ nickel bipyridine (Ni-bpy) cations as a model system and explore their structural reorganization on surfaces using a combination of experimental and computational approaches. The controlled preparation of surface layers by mass-selected deposition of Ni(bpy)32+ cations provides insights into the chemical reactivity of these species on surfaces. Both surface characterization using mass spectrometry and electronic structure calculations using density functional theory (DFT) indicate that Ni(bpy)32+ undergoes a substantial geometry distortion on surfaces in comparison with its gas-phase structure. This distortion reduces the ligand binding energy and facilitates the formation of the undercoordinated Ni(bpy)22+. Additionally, charge reduction by the soft landed Ni(bpy)32+ facilitates ligand loss. We observe that ligand loss is inhibited by co-depositing Ni(bpy)32+ with a stable anion such as closo-dodecaborate dianion, B12F122-. The strong electrostatic interaction between Ni(bpy)32+ and B12F122- diminishes the distortion of the cation due to interactions with the surface. This interaction stabilizes the soft landed cation by reducing the extent of charge reduction and its structural reorganization. Overall, this study shows the intricate interplay of charge state, ion surface interactions, and stabilization by counterions on the structure and reactivity of metal complexes on surfaces. The combined experimental and computational approach used in this study offers detailed insights into factors that affect the integrity and stability of active species relevant to energy production and catalysis.
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