Co‐Adsorption of O2 and CO on Au2−: Infrared Photodissociation Spectroscopy and Theoretical Study of [Au2O2(CO)n]− (n=2–6)

The co‐adsorption of O₂ and CO on anionic sites of gold species is considered as a crucial step in the catalytic CO oxidation on gold catalysts. In this regard, the [Au₂O₂(CO)_n]^? (n=2–6) complexes were prepared by using a laser vaporization supersonic ion source and were studied by using infrared photodissociation spectroscopy in the gas phase. All the [Au₂O₂(CO)_n]^? (n=2–6) complexes were characterized to have a core structure involving one CO and one O₂ molecule co‐adsorbed on Au₂^? with the other CO molecules physically tagged around. The CO stretching frequency of the [Au₂O₂(CO)]^? core ion is observed around =2032–2042 cm^?1, which is about 200 cm^?1 higher than that in [Au₂(CO)₂]^?. This frequency difference and the analyses based on density functional calculations provide direct evidence for the synergy effect of the chemically adsorbed O₂ and CO. The low lying structures with carbonate group were not observed experimentally because of high formation barriers. The structures and the stability (i.e., the inertness in a sense) of the co‐adsorbed O₂ and CO on Au₂^? may have relevance to the elementary reaction steps on real gold catalysts.     

Photochemistry and Reactivity of the Phenyl Radical–Water System: A Matrix Isolation and Computational Study

The reaction of the phenyl radical 1 with water has been investigated by using matrix isolation spectroscopy and quantum chemical calculations. The primary thermal product of the reaction between 1 and water is a weakly bound complex stabilized by an OH???π interaction. This complex is photolabile, and visible‐light irradiation (λ>420 nm) results in hydrogen atom transfer from water to radical 1 and the formation of a highly labile complex between benzene and the OH radical. This complex is stable under the conditions of matrix isolation, however, continuous irradiation with λ>420 nm light results in the complete destruction of the aromatic system and formation of an acylic unsaturated ketene. The mechanisms of all reaction steps are discussed in the light of ab initio and DFT calculations.     

Computational and Variable‐Temperature Infrared Spectroscopic Studies on Carbon Monoxide Adsorption on Zeolite Ca‐A

Bridged Ca ²⁺ ???CO???Ca ²⁺ complexes are formed on dual‐cation sites, constituted by a pair of nearby Ca²⁺ cations, when CO is adsorbed on zeolite Ca‐A. Two types of such species can be formed, designated S2–S1 and S1–S1 (see picture). Ca²⁺???CO monocarbonyl species are also identified, and at a relatively high CO equilibrium pressure, dicarbonyl complexes can also form.

     

Difluorophosphoryl Nitrene F2P(O)N: Matrix Isolation and Unexpected Rearrangement to F2PNO

Triplet difluorophosphoryl nitrene F₂P(O)N (X³A′′) was generated on ArF excimer laser irradiation (λ=193 nm) of F₂P(O)N₃ in solid argon matrix at 16 K, and characterized by its matrix IR, UV/Vis, and EPR spectra, in combination with DFT and CBS‐QB3 calculations. On visible light irradiation (λ>420 nm) at 16 K F₂P(O)N reacts with molecular nitrogen and some of the azide is regenerated. UV irradiation (λ=255 nm) of F₂P(O)N (X³A′′) induced a Curtius‐type rearrangement, but instead of a 1,3‐fluorine shift, nitrogen migration to give F₂PON is proposed to be the first step of the photoisomerization of F₂P(O)N into F₂PNO (difluoronitrosophosphine). Formation of novel F₂PNO was confirmed with ¹⁵N‐ and ¹⁸O‐enriched isotopomers by IR spectroscopy and DFT calculations. Theoretical calculations predict a rather long P? N bond of 1.922 Å [B3LYP/6‐311+G(3df)] and low bond‐dissociation energy of 76.3 kJ mol^?1 (CBS‐QB3) for F₂PNO.     

DFT Simulations of Water Adsorption and Activation on Low‐Index α‐Ga2O3 Surfaces

Density functional theory (DFT) calculations are used to explore water adsorption and activation on different α‐Ga₂O₃ surfaces, namely (001), (100), (110), and (012). The geometries and binding energies of molecular and dissociative adsorption are studied as a function of coverage. The simulations reveal that dissociative water adsorption on all the studied low‐index surfaces are thermodynamically favorable. Analysis of surface energies suggests that the most preferentially exposed surface is (012). The contribution of surface relaxation to the respective surface energies is significant. Calculations of electron local density of states indicate that the electron‐energy band gaps for the four investigated surfaces appears to be less related to the difference in coordinative unsaturation of the surface atoms, but rather to changes in the ionicity of the surface chemical bonds. The electrochemical computation is used to investigate the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on α‐Ga₂O₃ surfaces. Our results indicate that the (100) and (110) surfaces, which have low stability, are the most favorable ones for HER and OER, respectively.     

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-spectroscopic and density-functional-theory investigations of the LaCO, La2[eta2(mu2-C,O)], and c-La2(mu-C)(mu-O) molecules in solid argon

Reactions of laser-ablated lanthanum atoms with CO molecules in solid argon have been studied. The neutral lanthanum monocarbonyl (LaCO), produced upon sample deposition at 7 K, exhibits a C-O stretching frequency of 1772.7 cm(-1); to the best of our knowledge this is the lowest yet observed for a terminal CO in a neutral metal-carbonyl molecule (MCO, M = metal atom), implying anomalously enhanced metal-to-CO back-bonding. The infrared (IR) absorption band at 1145.9 cm(-1) is assigned to the C-O stretching mode of the side-on-bonding CO in the La2[eta2(mu2-C,O)] molecule. This CO-activated molecule undergoes an UV/Vis-photoinduced rearrangement to the CO-dissociated molecule, c-La2(mu-C)(mu-O). Density functional theory (DFT) calculations have been performed on these molecules, the results of which lend strong support to the experimental assignments of the IR spectra. LaCO is predicted to have a quartet ground state, corresponding to a linear geometry. Its formation involves La 6s-->4f promotion, which increases the strength of La-CO bonding by decreasing the sigma repulsion and, remarkably, by increasing the La 5d and 4f-->CO 2pi back-bonding. The observations schematically depict the whole process, starting with the interaction of CO with metal and ending with CO dissociation by the lanthanum dimer.     

Reactions of Th and U atoms with C2H2: infrared spectra and relativistic calculations of the metallacyclopropene, actinide insertion, and ethynyl products

Reactions of laser-ablated Th and U atoms with C(2)H(2) during condensation with excess argon at 7 K give several new product species. The metallacyclopropene, inserted hydride, and actinide ethynyl are identified from isotopic frequencies and relativistic DFT calculations. The higher-energy vinylidine isomer was not observed. These actinide metallacyclopropenes exhibit substantially stronger bonding interactions than found recently for the Pd and Pt metals. In the case of Th(C(2)H(2)) the argon matrix interaction is strong enough to reverse the computed order of states (MR-CISD) in favor of a triplet ground state for the (Ar)(n)(Th(C(2)H(2))) complex. The nature of the electronic interactions between various metal atoms and acetylene is compared and the origin of the particularly strong interaction for U and Th is traced to the higher energy of their 6d orbitals. The ThCCH and UCCH actinide ethynyl products are also observed and characterized by C[triple bond]C stretching modes 38+/-2 cm(-1) lower than acetylene itself.     

Reactions of uranium atoms with ammonia: infrared spectra and quasi-relativistic calculations of the U:NH3, H2N--UH, and HN==UH2 complexes

Ammonia molecules interact with U atoms, and the resulting U:NH3 complex rearranges upon visible irradiation to form the H2N--UH and HN==UH2 molecules in excess argon. These products are identified by functional group frequencies, 15NH3 and ND3 isotopic shifts, and comparison to frequencies calculated by using density functional theory. The N==U pi bond in HN==UH2 is enhanced by partial triple-bond character through N(2p) to U(5f) conjugation, which is comparable to that found in the analogous HN==ThH2 molecule. These products also form complexes with additional ammonia molecules in the matrix. The interesting higher-energy N[triple chemical bond]UH3 complex is not formed.     

Complexes of Formaldehyde and α-Dicarbonyls with Hydroxylamine: FTIR Matrix Isolation and Theoretical Study

The interactions of formaldehyde (FA), glyoxal (Gly) and methylglyoxal (MGly) with hydroxylamine (HA) isolated in solid argon and nitrogen were studied using FTIR spectroscopy and ab initio methods. The spectra analysis indicates the formation of two types of hydrogen-bonded complexes between carbonyl and hydroxylamine in the studied matrices. The cyclic planar complexes are stabilized by O–H⋯O(C), and C–H⋯N interactions and the nonplanar complexes are stabilized by O–H⋯O(C) bond. Formaldehyde was found to form with hydroxylamine, the cyclic planar complex and methylglyoxal, the nonplanar one in both argon and nitrogen matrices. In turn, glyoxal forms with hydroxylamine the most stable nonplanar complex in solid argon, whereas in solid nitrogen, both types of the complex are formed.     

Synthesis,Characterization, and Theoretical Investigation of Two‐Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π‐Accepting Carbenes

An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with π‐accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C‐Pd‐C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange‐colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)₂Pd/Pt] complexes can be quasi‐reversibly oxidized to their corresponding [(cAAC)₂Pd/Pt]⁺ cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations.     

Theoretical Study on the Spectroscopic Properties of CO3.−.nH2O Clusters: Extrapolation to Bulk

Vertical detachment energies (VDE) and UV/Vis absorption spectra of hydrated carbonate radical anion clusters, CO₃^.?.n H₂O (n=1–8), are determined by means of ab initio electronic structure theory. The VDE values of the hydrated clusters are calculated with second‐order Moller–Plesset perturbation (MP2) and coupled cluster theory using the 6‐311++G(d,p) set of basis functions. The bulk VDE value of an aqueous carbonate radical anion solution is predicted to be 10.6 eV from the calculated weighted average VDE values of the CO₃^.?.n H₂O clusters. UV/Vis absorption spectra of the hydrated clusters are calculated by means of time‐dependent density functional theory using the Becke three‐parameter nonlocal exchange and the Lee–Yang–Parr nonlocal correlation functional (B3LYP). The simulated UV/Vis spectrum of the CO₃^.?.8 H₂O cluster is in excellent agreement with the reported experimental spectrum for CO₃^.? (aq), obtained based on pulse radiolysis experiments.     

Difluoro‐λ5‐Phosphinonitrile F2PN: Matrix Isolation and Photoisomerization into FPNF

Splendid isolation : Monomeric phosphazene F₂PN (¹A₁) was prepared for the first time through irradiation of F₂PN₃ in an argon matrix with an ArF excimer laser (λ=193 nm). Upon subsequent irradiation with a high‐pressure mercury arc lamp (λ=255 nm), F₂PN undergoes a 1,2‐fluorine shift to give iminophosphane cis‐FP?NF.