Characterization of neutral metal hydride-hydroxide hydrogen-bonded clusters HMOH(H2O)2 (M = Al and Ga)

Metal hydride-hydroxide hydrogen-bonded clusters HMOH(H2O)n are key intermediates in the reactions of metals with water. However, characterizing the structure of such neutral clusters is a challenging experimental goal due to the difficulty of size selection. Here, neutral HMOH(H2O)2 (M = Al and Ga) clusters were prepared by using a laser-vaporization source and characterized by size-specific infrared-vacuum ultraviolet spectroscopy combined with quantum chemical calculations and ab initio molecular dynamics simulations. The HMOH(H2O)2 (M = Al and Ga) clusters were found to have intriguing hydrogen-bonded network structures. The results indicate that the formation of HMOH(H2O)2 (M = Al and Ga) is both thermodynamically exothermic and kinetically facile in the gas phase. The present system serves as a model for capturing key intermediates in metal-water reactions and also opens up new avenues for systematic studies of a large variety of reactions between neutral metal atoms/clusters and small molecules.

Investigation of the Proton-Bound Dimer of Dihydrogen Phosphate and Formate Using Infrared Spectroscopy in Helium Droplets

Understanding the structural and dynamic properties of proton-bound complexes is crucial for elucidating fundamental aspects of chemical reactivity and molecular interactions. In this work, the proton-bound complex between dihydrogen phosphate and formate, and its deuterated counterparts, is investigated using IR action spectroscopy in helium droplets. Contrary to the initial expectation that the stronger phosphoric acid would donate a proton to formate, both experiment and theory show that all exchangeable protons are located in the phosphate moiety. The experimental spectra show good agreement with both scaled harmonic and VPT2 anharmonic calculations, indicating that anharmonic effects are small. Some H-bending modes of the nondeuterated complex are found to be sensitive to the helium environment. In the case of the partially deuterated complexes, the experiments indicate that internal dynamics leads to isomeric interconversion upon IR excitation.

Development of Nontargeted Workflow of Occupational Exposure by Infrared Ion Spectroscopy and Silicone Wristbands' Passive Sampling

A new approach using orthogonal analytical techniques is developed for chemical identification. High resolution mass spectrometry and infrared ion spectroscopy are applied through a 5-level confidence paradigm to demonstrate the effectiveness of nontargeted workflow for the identification of hazardous organophosphates. Triphenyl phosphate is used as a surrogate organophosphate for occupational exposure, and silicone wristbands are used to represent personal samplers. Spectral data of a target compound is combined with spectral data of the sodium adduct and quantum chemical calculations to achieve a confirmed identification. Here, we demonstrate a nontargeted workflow that identifies organophosphate exposure and provides a mechanism for selecting validated methods for quantitative analyses.

Waste to wealth: Synthesis of hydrocalumite from Moroccan phosphogypsum and aluminum wastes

Each year, the phosphate industries in Morocco discard over 20 million tons of phosphogypsum into the Atlantic Ocean, posing a significant threat to aquatic life and causing potential long-term damage to ecosystems due to the accumulation of harmful substances. Hence, developing eco-friendly and cost-effective strategies to valorize phosphogypsum is vital to protect ecosystems and human health. This study aims to provide a concrete and efficient strategy for exploiting phosphogypsum and aluminum wastes in the preparation of hydrocalumite using the co-precipitation method. The synthesis strategy's effectiveness was assessed through a comprehensive analysis of the phosphogypsum-based hydrocalumite using various techniques, including FT-IR spectroscopy, X-ray powder diffraction, scanning electron microscopy (SEM), Energy-Dispersive X-Ray (EDX) analysis, X-ray fluorescence (XRF), and inductively coupled plasma optical emission spectrometry (ICP-OES). In addition, the structure was refined to discuss the arrangement of the polyhedrons occupied by the different ions in the hydrocalumite framework. It was found that the phosphogypsum-based hydrocalumite exhibited chemical and structural properties comparable to those of conventionally synthesized hydrocalumite, suggesting its potential applicability in diverse fields, including catalysis, cement and concrete production, polymer additives, medicine, and environmental remediation. Overall, in this work, the Moroccan phosphogypsum and aluminum wastes proved to be effective precursors of hydrocalumite, with structural and chemical properties presumably close to the conventional hydrocalumite.

The solvation of SOH group in hydrated HSO4−(H2O)n clusters

The S=O stretching and SOH bending peaks in the vibrational spectra of HSO4−(H2O) n, with n up to 6, are analyzed by both harmonic analysis and ab initio molecular dynamics simulation. The SOH bending mode is found to be much more sensitive to the extent of hydration and to the fluctuation of hydrogen bonds than the S=O stretching mode. The SOH donor hydrogen bond is gradually stabilized by n = 4, and further shortened up to n = 6, which is the key factor to understand the trend of evolution observed in the infrared multiple photon dissociation spectra.

Evolution of the linker in microhydrated hydrogen dinitrate anions: From H+ to H5 O2. J Comput Chem 2021;42:1514-1525. [PMID: 33990989 DOI: 10.1002/jcc.26560] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Hydrogen dinitrate anion, HNO₃ (NO₃ ^- ), is a proton-bound dimer with a very strong hydrogen bond. By employing ab initio molecular dynamics (AIMD) method, we studied the effects of the proton transfer and the rotation of the nitrates on the vibrational profiles of HNO₃ (NO₃ ^- )(H₂ O)_n (n = 0-2). The AIMD results indicate that the structure of the n = 0 cluster is very flexible, even though its hydrogen bond is quite strong. Significant rotations around the hydrogen bond and frequent transfers of proton from HNO₃ to NO₃ ^- are observed in AIMD simulations. Dynamic changes are therefore an important factor in understanding the broadening of vibrational features. For n = 1, the extent of structural fluctuation increases further, as H₂ O could move around the anion while the HNO₃ (NO₃ ^- ) core also goes through structural changes. Its vibrational spectrum can be understood as a mixture of many isomers visited during AIMD simulations. By n = 2, the structure is stabilized around one isomer, with the linker between the two nitrates being H₅ O₂ ⁺ , rather than H⁺ . Due to strong hydrogen bonds between nitrates and water molecules, this H₅ O₂ ⁺ takes the extraordinary structure with the H⁺ localized on one H₂ O, rather than being shared. While this novel structure is stable during AIMD simulations, the dynamic fluctuations in hydrogen bond distances still produce significant broadening in its vibrational profile.

Photoelectron Spectroscopy and Theoretical Study on Monosolvated Cyanate Analogue Clusters ECX-·Sol (ECX- = NCSe-, AsCSe-, and AsCS-; Sol = H2O, CH3CN)

Six monosolvated cyanate analogue clusters ECX^-·Sol (ECX^- = NCSe^-, AsCSe^-, and AsCS^-; Sol = H₂O and CH₃CN) were investigated using negative ion photoelectron spectroscopy (NIPES). NIPES experiments show that these clusters possess similar spectra overall compared to their respective isolated ECX^- anions but shift to higher electron binding energy with CH₃CN solvent, stabilizing the excess electrons slightly more than H₂O. For the ECX^-·H₂O series, vertical detachment energies and their increments relative to the bare species are measured to be 3.700/0.370, 3.085/0.415, and 3.085/0.430 eV for NCSe^-, AsCSe^- and AsCS^-, respectively, while the corresponding values in the ECX^-·CH₃CN series are 3.835/0.505, 3.145/0.475, and 3.135/0.480 eV. Ab initio electronic structure calculations indicate that the excess charges were located at the terminal N and Se atoms in NCSe^- and migrated to the central C atom in AsCSe^- and AsCS^-. For NCSe^-, the solvation is driven by the interactions with the two negatively charged terminal ends, while for AsCSe^- and AsCS^-, the solvation revolves around the interactions with the central C atom, where all the excess negative charge is concentrated. Two nearly degenerate isomers for NCSe^-·H₂O are identified, one forming a single strong N···H-O hydrogen bond (HB) and the other featuring a bidentate HB with two hydroxyl H atoms pointing to N and Se ends. In contrast, the negative central C atom in AsCSe^-/AsCS^- allows the formation of a bifurcated HB with H₂O. Similar effects are observed for the acetonitrile case, in which the three H atoms of the methyl group interact with the two negatively charged terminal ends in NCSe^-, while preferring to bind to the central negative carbon atom in AsCSe^-/AsCS^-. The different binding motifs derived in this work may suggest different solvation properties in NCSe^- versus AsCSe^-/AsCS^- with the former anion leading to asymmetric solvation at the N end of the solute, while the latter species creates more "isotropic" solvation around the central C equatorial plane.

Vibrational Signature of Dynamic Coupling of a Strong Hydrogen Bond

Elucidating the dynamic couplings of hydrogen bonds remains an important and challenging goal for spectroscopic studies of bulk systems, because their vibrational signatures are masked by the collective effects of the fluctuation of many hydrogen bonds. Here we utilize size-selected infrared spectroscopy based on a tunable vacuum ultraviolet free electron laser to unmask the vibrational signatures for the dynamic couplings in neutral trimethylamine-water and trimethylamine-methanol complexes, as microscopic models with only one single hydrogen bond holding two molecules. Surprisingly broad progression of OH stretching peaks with distinct intensity modulation over ∼700 cm^-1 is observed for trimethylamine-water, while the dramatic reduction of this progression in the trimethylamine-methanol spectrum offers direct experimental evidence for the dynamic couplings. State-of-the-art quantum mechanical calculations reveal that such dynamic couplings are originated from strong Fermi resonance between the stretches of hydrogen-bonded OH and several motions of the solvent water/methanol, such as translation, rocking, and bending, which are significant in various solvated complexes commonly found in atmospheric and biological systems.

Microhydration of Biomolecules: Revealing the Native Structures by Cold Ion IR Spectroscopy

The native-like structures of protonated glycine and peptide Gly₃H⁺ were elucidated using cold ion IR spectroscopy of these biomolecules hydrated by a controlled number of water molecules. The complexes were generated directly from an aqueous solution using gentle electrospray ionization. Already with a single retained water molecule, GlyH⁺ exhibits the native-like structure characterized by a lack of intramolecular hydrogen bonds. We use our spectra to calibrate the available data for the same complexes, which are produced by cryogenic condensation of water onto the gas-phase glycine. In some conformers of these complexes, GlyH⁺ adopts the native-like structure, while in the others, it remains "kinetically" trapped in the intrinsic state. Upon condensation of 4-5 water molecules, the embedded amino acid fully adopts its native-like structure. Similarly, condensation of one water molecule onto the tripeptide is insufficient to fully eliminate its kinetically trapped intrinsic states.

Size-Dependent Formation of an Ion Pair in HSO4-(H2O) n: A Molecular Model for Probing the Microsolvation of Acid Dissociation

With a p K_a of 2.0, HSO₄^- is not a strong acid as its dissociation percentage is only ∼10% in a solution of 1 M. However, our ab initio molecular dynamics and density functional theory calculations show that acid dissociation in the hydrate clusters, HSO₄^-(H₂O) _n, is quite facile at moderate sizes. It starts at around n = 12 and is completed by n = 16 when the energetics becomes very favorable. The dissociation explains the significant broadening at n = 16 in the S═O stretching region of the previously reported infrared photodissociation spectra for HSO₄^-(H₂O) _n as the solvation shell is tightened around the sulfate dianion and the proton. More importantly, HSO₄^-(H₂O) _n should provide an ideal model to probe the molecular details involved in an acid dissociation process.

Infrared photodissociation spectroscopy of ion-radical networks in cationic dimethylamine complexes

Infrared photodissociation spectroscopy was employed to establish the general trends in the stepwise growth motif of cationic dimethylamine (DMA)n+ (n = 4-13) complexes. Electronic structure calculations were performed to identify the structure of the low-lying isomers and to assign the observed spectral features. The results showed the preference of the formation of the proton-transferred (CH3)2NH2+ ion core. The (CH3)2NH2+-[(CH3)2N] ion-radical pair contact and the ion-radical separated pair could coexist at n = 4. The [(CH3)2N] radical is separated from the (CH3)2NH2+ ion core by one DMA molecule at n = 4-6 and by two or more DMA molecules in the larger clusters. This suggests that the (CH3)2NH2+-[(CH3)2N] ion-radical contact pair is not stable in the subsequent radiation-induced processes of DMA, and the [(CH3)2N] radical is released from the charged site in the cationic DMA networks.

Temperature-Dependent Infrared Photodissociation Spectroscopy of (CO2)3+ Cation

Infrared photodissociation spectra of He-buffer-gas-cooled (CO₂)₃⁺ were measured at ion trap temperatures of 15, 50, 150, and 280 K. Electronic structure calculations at the mPW2PLYPD/aug-cc-pVDZ level were performed to identify the structures of the low-lying isomers and to assign the observed spectral features. The experimental and calculated infrared spectra show that the (CO₂)₃⁺ cations formed in the source are primarily dominated by the charge partially delocalized C₂O₄⁺ motif, in which the positive charge is partially delocalized over the two CO₂ molecules. Thermal heating at elevated internal temperature supplies sufficient energy to overcome the isomerization barriers and gives access to the charge completely delocalized (CO₂) _n⁺ ( n = 3) motif, in which the positive charge is almost completely delocalized over all of the constituent CO₂ molecules.

Infrared Multiphoton Dissociation Spectroscopy with Free-Electron Lasers: On the Road from Small Molecules to Biomolecules

Infrared multiphoton dissociation (IRMPD) spectroscopy is commonly used to determine the structure of isolated, mass-selected ions in the gas phase. This method has been widely used since it became available at free-electron laser (FEL) user facilities. Thus, in this Minireview, we examine the use of IRMPD/FEL spectroscopy for investigating ions derived from small molecules, metal complexes, organometallic compounds and biorelevant ions. Furthermore, we outline new applications of IRMPD spectroscopy to study biomolecules.

Coordination-induced CO2 fixation into carbonate by metal oxides

Infrared spectroscopic studies reveal how the coordination induces CO₂ fixation into carbonate by a cationic yttrium oxide model catalyst.

Solvation effects on the N–O and O–H stretching modes in hydrated NO3−(H2O)n clusters

Ab initio molecular dynamics simulations reveal the solvation effects on the N–O and O–H stretching modes of NO₃⁻(H₂O)_n.

Solvation effects on the vibrational modes in hydrated bicarbonate clusters

Harmonic analysis and ab initio molecular dynamics simulations reveal the solvation effects on the vibrational modes of HCO₃⁻(H₂O)_n.

Probing the microhydration of metal carbonyls: a photoelectron velocity-map imaging spectroscopic and theoretical study of Ni(CO)3(H2O)n. Phys Chem Chem Phys 2016;18:26719-26724. [PMID: 27711570 DOI: 10.1039/c6cp05035b]

A series of microhydrated nickel carbonyls, Ni(CO)₃(H₂O)_n^- (n = 0-4), are prepared via a laser vaporization supersonic cluster source in the gas phase and identified by mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations. Vertical detachment energies for the n = 1-4 anions are measured from the photoelectron spectra to be 1.429 ± 0.103, 1.698 ± 0.090, 1.887 ± 0.080, and 2.023 ± 0.074 eV, respectively. The C-O stretching vibrational frequencies in the corresponding neutral clusters are determined to be 1968, 1950, 1945, and 1940 cm^-1 for n = 1-4, respectively, which are characteristic of terminal CO. It is determined that the hydrogen atom of the first water molecule is bound to the nickel center. Addition of a second water molecule prefers solvation at the carbonyl terminal. Spectroscopy combined with theory suggests that the solvation of nickel tricarbonyl is dominated by a water-ring network. The present findings would have important implications for the fundamental understanding of the multifaceted mechanisms of the multibody interaction of water and carbon monoxide with transition metals.

Probing the microsolvation of a quaternary ion complex: gas phase vibrational spectroscopy of (NaSO4−)2(H2O)n=0–6, 8

We report infrared multiple photon dissociation spectra of cryogenically-cooled (NaSO₄⁻)₂(H₂O)_n dianions (n = 0–6, 8) in the fingerprint spectral region, which provide evidence for a remarkable stability of the quaternary ion complex upon microhydration.

Anharmonicities and coherent vibrational dynamics of phosphate ions in bulk H2O

2D IR spectroscopy reveals Fermi resonances and long lived quantum beats for phosphate ions in water.