IR spectrum of SiHOHSiH: cationic OH⋯HSi dihydrogen bond charge-inverted SiH⋯Si hydrogen bond.

The low electronegativity of Si gives rise to a variety of nonconventional intermolecular interactions in clusters of silanes and their derivatives, which have not been well characterized yet. Herein, we characterize the structures of various isomers of bare and Ar-tagged SiHOHSiH dimers composed of protonated silanol and silane by infrared photodissociation (IRPD) of mass-selected ions and dispersion-corrected density functional calculations (B3LYP-D3/aug-cc-pVTZ). The analysis of the IRPD spectra recorded in the OH stretch range reveals the competition between two types of nonconventional hydrogen bonds (H-bonds).

Infrared spectra of SiH ions ( = 2-8): inorganic H-(Si-H) hydride wires of penta-coordinated Si in 3c-2e and charge-inverted hydrogen bonds.

SiH cations are important constituents in silane plasmas and astrochemical environments. Protonated disilane (SiH) was shown to have a symmetric three-centre two-electron (3c-2e) Si-H-Si bond that can also be considered as a strong ionic charge-inverted hydrogen bond with polarity Si-H-Si. Herein, we extend our previous work to larger SiH cations, formally resulting from adding SiH molecules to a SiH core.

Microhydration of the adamantane cation: intracluster proton transfer to solvent in [Ad(HO)] for ≥ 3.

Radical cations of diamondoids are important intermediates in their functionalization reactions in polar solvents. To explore the role of the solvent at the molecular level, we characterize herein microhydrated radical cation clusters of the parent molecule of the diamondoid family, adamantane (CH, Ad), by infrared photodissociation (IRPD) spectroscopy of mass-selected [Ad(HO)] clusters. IRPD spectra of the cation ground electronic state recorded in the CH/OH stretch and fingerprint ranges reveal the first steps of this fundamental H-substitution reaction at the molecular level.

Microhydrated clusters of a pharmaceutical drug: infrared spectra and structures of amantadineH(HO).

Solvation of pharmaceutical drugs has an important effect on their structure and function. Analysis of infrared photodissociation spectra of amantadineH(HO) clusters in the sensitive OH, NH, and CH stretch range by quantum chemical calculations (B3LYP-D3/cc-pVTZ) provides a first impression of the interaction of this pharmaceutically active cation with water at the molecular level. The size-dependent frequency shifts reveal detailed information about the acidity of the protons of the NH group of N-protonated amantadineH (AmaH) and the strength of the NH⋯O and OH⋯O hydrogen bonds (H-bonds) of the hydration network.

Infrared spectra and structures of protonated amantadine isomers: detection of ammonium and open-cage iminium ions.

The protonated form of amantadine (1-CHNH, Ama), the amino derivative of adamantane (CH, Ada), is a wide-spread antiviral and anti-Parkinsonian drug and plays a key role in many pharmaceutical processes. Recent studies reveal that the adamantyl cage (CH) of Ama can open upon ionization leading to distonic bicyclic iminium isomers, in addition to the canonical nascent Ama isomer. Herein, we study protonation of Ama using infrared photodissociation spectroscopy (IRPD) of Ar-tagged ions and density functional theory calculations to characterize cage and open-cage isomers of AmaH and the influence of the electron-donating NH group on the cage-opening reaction potential.

Opening of the Diamondoid Cage upon Ionization Probed by Infrared Spectra of the Amantadine Cation Solvated by Ar, N , and H O.

Radical cations of diamondoids, a fundamental class of very stable cyclic hydrocarbon molecules, play an important role in their functionalization reactions and the chemistry of the interstellar medium. Herein, we characterize the structure, energy, and intermolecular interaction of clusters of the amantadine radical cation (Ama , 1-aminoadamantane) with solvent molecules of different interaction strength by infrared photodissociation (IRPD) spectroscopy of mass-selected Ama L clusters, with L=Ar (n≤3) and L=N and H O (n=1), and dispersion-corrected density functional theory calculations (B3LYP-D3/cc-pVTZ). Three isomers of Ama generated by electron ionization are identified by the vibrational properties of their rather different NH groups.

Infrared Spectrum of the Amantadine Cation: Opening of the Diamondoid Cage upon Ionization.

Radical cations of diamondoids, a fundamental class of highly stable cycloalkanes, are intermediates in functionalization reactions and possibly present in the interstellar medium. Herein, we characterize the structure of the radical cation of 1-amantadine (1-CHNH, Ama), the amino derivative of the parent adamantane (CH, Ada), by infrared spectroscopy and density functional theory calculations. The structural isomers of Ama produced by electron ionization are probed by infrared photodissociation of cold Ar-tagged ions.

Microhydration of substituted diamondoid radical cations of biological relevance: infrared spectra of amantadine-(HO) clusters.

Hydration of biomolecules and pharmaceutical compounds has a strong impact on their structure, reactivity, and function. Herein, we explore the microhydration structure around the radical cation of the widespread pharmaceutical drug amantadine (C16H15NH2, Ama) by infrared photodissociation (IRPD) spectroscopy of mass-selected Ama+Wn = 1-3 clusters (W = H2O) recorded in the NH, CH, and OH stretch range of the cation ground electronic state. Analysis of the size-dependent frequency shifts by dispersion-corrected density functional theory calculations (B3LYP-D3/cc-pVTZ) provides detailed information about the acidity of the protons of the NH2 group of Ama+ and the structure and strength of the NHO and OHO hydrogen bonds (H-bonds) of the hydration network.

Infrared Spectrum of the Adamantane -Water Cation: Hydration-Induced C-H Bond Activation and Free Internal Water Rotation.

Diamondoid cations are reactive intermediates in their functionalization reactions in polar solution. Hydration is predicted to strongly activate their C-H bonds in initial proton abstraction reactions. To study the effects of microhydration on the properties of diamondoid cations, we characterize herein the prototypical monohydrated adamantane cation (C H -H O, Ad -W) in its ground electronic state by infrared photodissociation spectroscopy in the CH and OH stretch ranges and dispersion-corrected density functional theory (DFT) calculations.

IR Spectrum and Structure of Protonated Monosilanol: Dative Bonding between Water and the Silylium Ion.

We report the spectroscopic characterization of protonated monosilanol (SiH OH ) isolated in the gas phase, thus providing the first experimental determination of the structure and bonding of a member of the elusive silanol family. The SiH OH ion is generated in a silane/water plasma expansion, and its structure is derived from the IR photodissociation (IRPD) spectrum of its Ar cluster measured in a tandem mass spectrometer. The chemical bonding in SiH OH is analyzed by density functional theory (DFT) calculations, providing detailed insight into the nature of the dative H Si -OH bond.

Infrared spectrum of the Si3H8+ cation: evidence for a bridged isomer with an asymmetric three-center two-electron Si-H-Si bond.

The IR spectrum of Si3H8(+) ions produced in a supersonic plasma molecular beam expansion of SiH4, He, and Ar is inferred from photodissociation of cold Si3H8(+)-Ar complexes. Vibrational analysis of the spectrum is consistent with a Si3H8(+) structure (2(+)) obtained by a barrierless addition reaction of SiH4 to the disilene ion (H2Si=SiH2(+)) in the silane plasma. In this structure, one of the electronegative H atoms of SiH4 donates electron density into the partially filled electrophilic π orbital of the disilene cation.

Infrared spectrum of the disilane cation (Si2H6+) from Ar-tagging spectroscopy.

The infrared spectrum of the disilane cation, Si(2)H(6)(+), in its (2)A(1g) ground state is inferred from photodissociation of cold Si(2)H(6)(+)-Ar(n) complexes (n = 1, 2). Vibrational analysis is consistent with a D(3d) symmetric structure of H(3)SiSiH(3)(+) generated by ionization from the bonding σ(SiSi) orbital. Structural, vibrational, and electronic properties of Si(2)H(6)((+)) and Si(2)H(6)(+)-Ar(1,2) are determined at the MP2/aug-cc-pVTZ and B3LYP/aug-cc-pVTZ levels.