The Nature of Bonding between Argon and Mixed Gold–Silver Trimers

The controversial nature of chemical bonding between noble gases and noble metals is addressed. Experimental evidence of exceptionally strong Au? Ar bonds in Ar complexes of mixed Au? Ag trimers is presented. IR spectra reveal an enormous influence of the attached Ar atoms on vibrational modes, particularly in Au‐rich trimers, where Ar atoms are heavily involved owing to a relativistically enhanced covalency. In Ag‐rich trimers, vibrational transitions of the metal framework predominate, indicating a pure electrostatic character of the Ag? Ar bonds. The experimental findings are analyzed by means of DFT calculations, which show how the relativistic differences between Au and Ag are manifested in stronger Au? Ar binding energies. Because of the ability to vary composition and charge distribution, the trimers serve as ideal model systems to study the chemical nature of the bonding of noble gases to closed‐shell systems containing gold.     

Analyzing the Vibrational Signatures of Thiophenol Adsorbed on Small Gold Clusters by DFT Calculations

Using density functional theory, we calculate the IR and Raman signatures of the thiophenol (TP) molecule adsorbed on gold clusters by mimicking the different types of adsorption sites, and we analyze these signatures by using advanced tools implemented into the pyvib2 program. First, we follow the evolution of the vibrational normal modes from the isolated TP molecule to those of TP adsorbed on different clusters to highlight the influence of the site of adsorption on the vibrational motions. The use of the overlap matrix between the modes enables mode permutations, mode mixings, and mode splittings to be highlighted, all of which depend not only on the adsorption but also on the type of cluster and its symmetry. Second, the IR and Raman signatures were analyzed by using group coupling matrices and atomic contribution patterns based on the Hug decomposition scheme. Key results include 1) the fact that Raman spectroscopy is more sensitive than IR spectroscopy with respect to the nature of the coordination site, 2) an IR criterion that distinguishes between on‐top coordination (onefold coordinated) with respect to the bridge (twofold coordinated) and hexagonal close‐packed hollow site coordination (threefold coordinated), and 3) the best agreement to the experimental Raman spectrum with regard to signatures in the 500 to 1200 cm^?1 region is obtained for bridged, twofold coordination.     

Ultrafast Structural Fluctuations of Myoglobin‐Bound Thiocyanate and Selenocyanate Ions Measured with Two‐Dimensional Infrared Photon Echo Spectroscopy

Structural dynamics within the distal cavity of myoglobin protein is investigated using 2D‐IR and IR pump–probe spectroscopy of the N≡C stretch modes of heme‐bound thiocyanate and selenocyanate ions. Although myoglobin‐bound thiocyanate group shows a doublet in its IR absorption spectrum, no cross peaks originating from chemical exchange between the two components are observed in the time‐resolved 2D IR spectra within the experimental time window. Frequency–frequency correlation functions of the two studied anionic ligands are obtained by means of a few different analysis approaches; these functions were then used to elucidate the differences in structural fluctuation around ligand, ligand–protein interactions, and the degree of structural heterogeneity within the hydrophobic pocket of these myoglobin complexes.     

Infrared and Raman Spectroscopy of Methylcyanodiacetylene (CH3C5N)

A spectroscopic study combining IR absorption and Raman scattering is presented for methylcyanodiacetylene (CH₃C₅N). Gas‐phase, cryogenic matrix‐isolated, and pure solid‐phase substance was analyzed. Out of 16 normal vibrational modes, 14 were directly observed. The analysis of the spectra was assisted by quantum chemical calculations of vibrational frequencies, IR absorption intensities, and Raman scattering activities at density functional theory and ab initio levels. Previous assignments of gas‐phase IR absorption bands were revisited and extended.     

Ultrafast 2D-IR spectroscopy of transient species.

Multidimensional spectroscopic experiments offer fascinating insights into molecular structure and dynamics in the field of NMR spectroscopy. With the introduction of ultrafast two-dimensional infrared spectroscopy (2D-IR), multidimensional concepts have entered the optical domain, measuring couplings and correlations between molecular vibrations with femtosecond time resolution. In the transient 2D-IR (T2D-IR) experiments described in this minireview we exploit the high time resolution of 2D-IR to study transient species during fast nonequilibrium processes in real time. Information on molecular structure and dynamics is obtained that is not available from one-dimensional spectroscopy. We discuss examples from chemistry, physics and biophysics.     

Infrared Absorption Spectra of t‐HNOH Radicals Generated on VUV Irradiation of NO in Solid Hydrogen

Photoproduct signature: Irradiation of solid hydrogen near 3 K containing NO with vacuum‐UV light from synchrotron radiation yields new infrared absorption lines at 1241.7, 1063.6 and 726.2 cm^?1 (see figure). These new lines are assigned to vibrational modes of t‐HNOH. This photoproduct is formed from electronically excited NO reacting with neighboring hydrogen in the solid sample.

     

Molecular Details on Multiple Cofactor Containing Redox Metalloproteins Revealed by Infrared and Resonance Raman Spectroscopies

Vibrational spectroscopy and in particular, resonance Raman (RR) spectroscopy, can provide molecular details on metalloproteins containing multiple cofactors, which are often challenging for other spectroscopies. Due to distinct spectroscopic fingerprints, RR spectroscopy has a unique capacity to monitor simultaneously and independently different metal cofactors that can have particular roles in metalloproteins. These include e.g., (i) different types of hemes, for instance hemes c, a and a₃ in caa₃-type oxygen reductases, (ii) distinct spin populations, such as electron transfer (ET) low-spin (LS) and catalytic high-spin (HS) hemes in nitrite reductases, (iii) different types of Fe-S clusters, such as 3Fe-4S and 4Fe-4S centers in di-cluster ferredoxins, and (iv) bi-metallic center and ET Fe-S clusters in hydrogenases. IR spectroscopy can provide unmatched molecular details on specific enzymes like hydrogenases that possess catalytic centers coordinated by CO and CN⁻ ligands, which exhibit spectrally well separated IR bands. This article reviews the work on metalloproteins for which vibrational spectroscopy has ensured advances in understanding structural and mechanistic properties, including multiple heme-containing proteins, such as nitrite reductases that house a notable total of 28 hemes in a functional unit, respiratory chain complexes, and hydrogenases that carry out the most fundamental functions in cells.     

Infrared spectrum and structure of thorimine (HN=ThH2)

Laser-ablated thorium atoms react with ammonia to form thorimine (NH=ThH(2)), the first actinide imine to be reported. This work underscores the high reactivity of thorium atoms, particularly for N-H bond activation, reveals a new type of multiple bond to actinide atoms, and shows that this bond is strong for thorium as a result of an important contribution from the f orbitals.     

Infrared spectrum and structure of the adamantane cation: direct evidence for Jahn-Teller distortion

The fundamentals: the IR spectrum of the adamantane cation, C(10)H(16)(+), has been derived by resonant IR photodissociation of weakly bound C(10)H(16)(+)?L(n) clusters. The analysis of the IR spectrum provides the first spectroscopic characterization of this fundamental cycloalkane carbocation in the gas phase and direct evidence for the Jahn-Teller distortion in the (2)A(1) ground electronic state.     

Controlled synthesis of noble metallic dimers and the influence of secondary metals on the catalytic activity

To precisely discuss the influence of secondary metals on the whole nanosystem, two different types of Pd/Au dimers are constructed by reducing Au precursors with or without ascorbic acid. The number and size of gold nanoparticles attaching on larger Pd nanocrystals can be roughly controlled. Furthermore, based on electrocatalysis, we find that multidecorated dimers are generally more active than singly decorated ones. Meanwhile, the amount of Au precursor used in preparing multidecorated dimers is found to be very important to the catalytic activity of the as-prepared catalysts. The performance of the catalyst is enhanced with the increasing of Au precursor when the Au/Pd molar ratio is below 1:4, but hindered when the ratio climbs higher. Finally, this work provides a promising approach in forming hybrid nanocompositions to find an optimized amount of secondary metal, which is of significance in academic and economic fields.     

The extended view on the empty C2(3)-C82 fullerene: isolation, spectroscopic, electrochemical, and spectroelectrochemical characterization and DFT calculations

An extended study of the spectroscopic and redox properties of the C(82) fullerene is presented. Among the nine isolated-pentagon-rule (IPR) isomers of the C(82) fullerene the C(82)(3) isomer with C(2) symmetry is the only stable, empty fullerene structure formed in the arc burning process that can be isolated in an isomerically pure form. Here, its formation and isolation are described and its structure is confirmed by experimental spectroscopic studies as well as time-dependent DFT calculations. The electrochemistry of the C(82)(3) isomer is studied in detail by cyclic voltammetry and spectroelectrochemistry. The anionic species of C(82) with the charge ranging from C(82) (-) to C(82) (4-) were successively generated in o-dichlorobenzene solution at room temperature and characterized by in situ ESR and visible/near-infrared (Vis/NIR) spectroscopy. The data give new insights into the charged states of the C(82)(3) fullerene.