Covalent Bonding Between Be+ and CO2 in BeOCO+ with a Surprisingly High Antisymmetric OCO Stretching Vibration.

The cationic complex BeOCO+ is produced in a solid neon matrix. Infrared absorption spectroscopic study shows that it has a very high antisymmetric OCO stretching vibration of 2418.9 cm-1, which is about 71 cm-1 blue-shifted from that of free CO2. The quantum chemical calculations are in very good agreement with the experimental observation. Depending on the theoretical method, a linear or quasi-linear structure is predicted for the cation. The analysis of the electronic structure shows that the bonding of Be+ to one oxygen atom induces very little charge migration between the two moieties, but it causes a significant change in the σ-charge distribution that strengthens the terminal C-O bond, leading to the observed blue shift. The bonding analysis reveals that the Be+ ← OCO donation results in strong binding due to the interference of the wave function and a charge polarization within the CO2 fragment and hybridization to Be+ but only negligible charge donation.

Boron-Mediated Carbon-Carbon Bond Cleavage and Rearrangement of Benzene Forming the Borepinyl Radical and Borole Derivatives.

The reaction of atomic boron with benzene in solid neon has been investigated by matrix isolation infrared spectroscopy with isotopic substitutions as well as quantum chemical calculations. The reaction is initiated by boron atom addition to benzene in forming an η2-(1, 4) π adduct (A). A borepinyl radical (B) formed by C-C bond insertion is also observed on annealing. The η2-(1,4) π adduct photoisomerizes to an unprecedented borole substituted vinyl radical intermediate (C) via ring-opening and rearrangement reactions involving an antiaromatic borole subunit. A previously unconsidered 1-ethynyl-2-dihydro-1H-borole radical (D) is generated as the final product under UV light irradiation. The results presented herein give new insight into the benzene carbon-carbon bond cleavage and rearrangement reactions mediated by a nonmetal and provide a possible route for the construction of heterocyclic borepinyl and borole species via benzene ring opening and rearrangement reactions.

Formation and Characterization of a BeOBeC Multiple Radical Featuring a Quartet Carbyne Moiety.

Through reaction of beryllium dimers with carbon monoxide, a carbonyl complex BeBeCO is formed in solid neon. Upon visible light excitation, the BeBeCO complex rearranges to a BeCOBe isomer, which further isomerizes to a low-energy BeOBeC species under UV-visible light excitation. These species are identified on the basis of infrared absorption spectroscopy with isotopic substitutions and quantum chemical studies. The BeOBeC molecule is characterized to be a multiple radical species having an electronic quintet ground state featuring an unusual quartet carbyne unit with three unpaired electrons on the carbon center. Bonding analysis indicates that the strong Pauli repulsion between carbon 2s lone pair electrons and the σ electrons of the BeOBe fragment significantly weakens the Be-C bonding and destabilizes the triplet state of the BeOBeC radical with a doublet carbyne unit. The three-center π-bonding of BeOBe is also found to play a role in stabilizing the quartet carbyne.

A Very Short Be-Be Distance but No Bond: Synthesis and Bonding Analysis of Ng-Be2 O2 -Ng' (Ng, Ng'=Ne, Ar, Kr, Xe).

Short interatomic distances below standard values for a single bond are usually identified with double or triple bonds. The synthesis and spectroscopic characterization of a molecule is reported where the distance between two beryllium atoms is shorter than a standard double bond but there is no bond. The cyclic diberyllium dioxide Be2 O2 molecule, which is coordinated by two noble gas atoms in Ng-Be2 O2 -Ng' (Ng, Ng'=Ne, Ar, Kr, Xe) was isolated and spectroscopically identified in low-temperature matrices. The complexes possess very short Be-Be distances, but the analysis of the electronic structure reveals that there is no chemical bond.

Photoassisted Homocoupling of Methyl Iodide Mediated by Atomic Gold in Low-Temperature Neon Matrix.

Infrared spectroscopy and density functional theory calculations showed that the gold complexes [CH3-Au-I] and [(CH3)2-Au-I2], in which one and two CH3I molecule(s), respectively, are oxidatively adsorbed on the Au atoms, are formed in a solid neon matrix via reactions between laser-ablated gold atoms and CH3I. Global reaction route mapping calculations revealed that the heights of the activation barriers for the sequential oxidative additions to produce [CH3-Au-I] and [(CH3)2-Au-I2] are 0.53 and 1.00 eV, respectively, suggesting that the reactions proceed via electronically excited states. The reductive elimination of ethane (C2H6) from [(CH3)2-Au-I2] leaving AuI2 was hindered by an activation barrier as high as 1.22 eV but was induced by visible-light irradiation on [(CH3)2-Au-I2]. These results demonstrate that photoassisted homocoupling of CH3I is mediated by Au atoms via [(CH3)2-Au-I2] as an intermediate.

Observation of Main-Group Tricarbonyls [B(CO)3 ] and [C(CO)3 ](+) Featuring a Tilted One-Electron Donor Carbonyl Ligand.

A combined experimental and theoretical study on the main-group tricarbonyls [B(CO)3 ] in solid noble-gas matrices and [C(CO)3 ](+) in the gas phase is presented. The molecules are identified by comparing the experimental and theoretical IR spectra and the vibrational shifts of nuclear isotopes. Quantum chemical ab initio studies suggest that the two isoelectronic species possess a tilted η(1) (µ1 -CO)-bonded carbonyl ligand, which serves as an unprecedented one-electron donor ligand. Thus, the central atoms in both complexes still retain an 8-electron configuration. A thorough analysis of the bonding situation gives quantitative information about the donor and acceptor properties of the different carbonyl ligands. The linearly bonded CO ligands are classical two-electron donors that display classical σ-donation and π-back-donation following the Dewar-Chatt-Duncanson model. The tilted CO ligand is a formal one-electron donor that is bonded by σ-donation and π-back-donation that involves the singly occupied orbital of the radical fragments [B(CO)2 ] and [C(CO)2 ](+) .

Carbon Dioxide Activation by Scandium Atoms and Scandium Monoxide Molecules: Formation and Spectroscopic Characterization of ScCO3 and OCScCO3 in Solid Neon.

The reactions of carbon dioxide with scandium monoxide molecules and scandium atoms are investigated using matrix isolation infrared spectroscopy in solid neon. The species formed are identified by the effects of isotopic substitution on their infrared spectra as well as density functional calculations. The results show that the ground state ScO molecule reacts with carbon dioxide to form the carbonate complex ScCO3 spontaneously on annealing. The ground state Sc atom reacts with two carbon dioxide molecules to give the carbonate carbonyl complex OCScCO3 via the previously reported OScCO insertion intermediate on annealing. The observation of these spontaneous reactions is consistent with theoretical predictions that both the Sc + 2CO2 → OCScCO3 and ScO + CO2 → ScCO3 reactions are thermodynamically exothermic and are kinetically facile, requiring little or no activation energy.

Observation of Spontaneous C=C Bond Breaking in the Reaction between Atomic Boron and Ethylene in Solid Neon.

A ground-state boron atom inserts into the C=C bond of ethylene to spontaneously form the allene-like compound H2 CBCH2 on annealing in solid neon. This compound can further isomerize to the propyne-like HCBCH3 isomer under UV light excitation. The observation of this unique spontaneous C=C bond insertion reaction is consistent with theoretical predictions that the reaction is thermodynamically exothermic and kinetically facile. This work demonstrates that the stronger C=C bond, rather than the less inert C-H bond, can be broken to form organoboron species from the reaction of a boron atom with ethylene even at cryogenic temperatures.

The Oxygen-Rich Beryllium Oxides BeO4 and BeO6.

Two novel isomers of BeO4 with the structures OBeOOO and OBe(O3 ) in the electronic triplet state have been prepared as well as the known disuperoxide complex Be(O2 )2 in solid noble-gas matrices. We also report the synthesis of the oxygen-rich bis(ozonide) complex Be(O3 )2 in the triplet state which has a D2d equilibrium geometry. The molecular structures were identified by infrared absorption spectroscopy with isotopic substitutions as well as quantum chemical calculations.

Pentavalent Lanthanide Compounds: Formation and Characterization of Praseodymium(V) Oxides.

The chemistry of lanthanides (Ln=La-Lu) is dominated by the low-valent +3 or +2 oxidation state because of the chemical inertness of the valence 4f electrons. The highest known oxidation state of the whole lanthanide series is +4 for Ce, Pr, Nd, Tb, and Dy. We report the formation of the lanthanide oxide species PrO4 and PrO2 (+) complexes in the gas phase and in a solid noble-gas matrix. Combined infrared spectroscopic and advanced quantum chemistry studies show that these species have the unprecedented Pr(V) oxidation state, thus demonstrating that the pentavalent state is viable for lanthanide elements in a suitable coordination environment.

Experimental and theoretical studies of the infrared spectra and bonding properties of NgBeCO3 and a comparison with NgBeO (Ng = He, Ne, Ar, Kr, Xe).

The novel neon complex NeBeCO3 has been prepared in a low-temperature neon matrix via codeposition of laser-evaporated beryllium atoms with O2 + CO/Ne. Doping by the heavier noble gas atoms argon, krypton and xenon yielded the associated adducts NgBeCO3 (Ng = Ar, Kr, Xe). The noble gas complexes have been identified via infrared spectroscopy. Quantum chemical calculations of NgBeCO3 and NgBeO (Ng = He, Ne, Ar, Kr, Xe) using ab initio methods and density functional theory show that the Ng-BeCO3 bonds are slightly longer and weaker than the Ng-BeO bonds. The energy decomposition analysis of the Ng-Be bonds suggests that the attractive interactions come mainly from the Ng → BeCO3 and Ng → BeO σ donation.

Infrared Photodissociation Spectroscopy of the Ni(O2)n(+) (n = 2-4) Cation Complexes.

The infrared spectra of mass-selected Ni(O2)n(+) (n = 2-4) and their argon-tagged complexes are measured by infrared photodissociation spectroscopy in the gas phase. The experimental spectra provide distinctive patterns allowing the determination of their geometric and electronic structures by comparison with the simulated vibrational spectra from density functional theory calculations. The [Ni(O2)2Ar2](+) cation complex was determined to have D2h symmetry involving a Ni(O2)2(+) core ion with two equivalent superoxide ligands side-on bound to a Ni(3+) cation center. The higher Ni(O2)3(+) and Ni(O2)4(+) cation complexes were determined to have structures with a chemically bound Ni(O2)2(+) core ion that is weakly coordinated by neutral O2 molecule(s).

Carbon monoxide bonding with BeO and BeCO3 : surprisingly high CO stretching frequency of OCBeCO3.

The complexes OCBeCO3 and COBeCO3 have been isolated in a low-temperature neon matrix. The more stable isomer OCBeCO3 has a very high CO stretching mode of 2263 cm(-1) , which is blue-shifted by 122 cm(-1) with respect to free CO and 79 cm(-1) higher than in OCBeO. Bonding analysis of the complexes shows that OCBeO has a stronger OCBeY bond than OCBeCO3 because it encounters stronger π backdonation. The isomers COBeCO3 and COBeO exhibit red-shifted CO stretching modes with respect to free CO. The inverse change of CO stretching frequency in OCBeY and COBeY is explained with the reversed polarization of the σ and π bonds in CO.

Formation and characterization of the boron dicarbonyl complex [B(CO)2](-).

We report the synthesis and spectroscopic characterization of the boron dicarbonyl complex [B(CO)2 ](-) . The bonding situation is analyzed and compared with the aluminum homologue [Al(CO)2 ](-) using state-of-the-art quantum chemical methods.

Infrared spectra and structures of the neutral and charged CrCO2 and Cr(CO2)2 isomers in solid neon.

The reactions from codeposition of laser-ablated chromium atoms with carbon dioxide in excess neon are studied by infrared absorption spectroscopy. The species formed are identified by the effects of isotopic substitution on their infrared spectra. Density functional calculations are performed to support the spectral assignments and to interpret the geometric and electronic structures of the experimentally observed species. Besides the previously reported insertion products OCrCO and O2Cr(CO)2, the one-to-one Cr(CO2) complex and the one-to-two Cr(CO2)2 complex as well as the CrOCrCO and OCCrCO3 complexes are also formed. The Cr(CO2) complex is characterized to be side-on η(2)-C,O-coordinated. The Cr(CO2)2 complex is identified to involve a side-on η(2)-C,O-coordinated CO2 and an end-on η(1)-O-coordinated CO2. OCCrCO3 is a carbonate carbonyl complex predicted to have a planar structure with a η(2)-O,O-coordinated carbonate ligand. The CrOCrCO complex is predicted to be linear with a high-spin ground state. Besides the neutral molecules, charged species are also produced. The Cr(CO2)(+) and Cr(CO2)2(+) cation complexes are characterized to have linear end-on η(1)-O-coordinated structures with blue-shifted antisymmetric CO2 stretching vibrational frequencies. The OCrCO(-) anion is bent with the Cr-O and CO stretching frequencies red-shifted from those of OCrCO neutral molecule.

Reactions of vanadium dioxide molecules with acetylene: infrared spectra of VO2(η(2)-C2H2)(x) (x = 1, 2) and OV(OH)CCH in solid neon.

Reactions of vanadium dioxide molecules with acetylene have been studied by matrix isolation infrared spectroscopy. Reaction intermediates and products are identified on the basis of isotopic substitutions as well as density functional frequency calculations. Ground state vanadium dioxide molecule reacts with acetylene in forming the side-on-bonded VO2(η(2)-C2H2) and VO2(η(2)-C2H2)2 complexes spontaneously on annealing in solid neon. The VO2(η(2)-C2H2) complex is characterized to have a (2)B2 ground state with C2v symmetry, whereas the VO2(η(2)-C2H2)2 complex has a (2)A ground state with C2 symmetry. The VO2(η(2)-C2H2) and VO2(η(2)-C2H2)2 complexes are photosensitive. The VO2(η(2)-C2H2) complex rearranges to the OV(OH)CCH molecule upon UV-vis light excitation.

Formation and infrared spectroscopic characterization of three oxygen-rich BiO4 isomers in solid argon.

The reactions of bismuth atoms and O2 have been investigated using matrix isolation infrared spectroscopy and density functional theory calculations. The ground state bismuth atoms react with dioxygen to form the BiOO and Bi(O2)2 complexes spontaneously on annealing. The BiOO molecule is characterized to be an end-on bonded superoxide complex, while the Bi(O2)2 molecule is characterized to be a superoxo bismuth peroxide complex, [Bi(3+)(O2(-))(O2(2-))]. Under UV-visible light irradiation, the Bi(O2)2 complex rearranges to the more stable OBiOOO isomer, an end-on bonded bismuth monoxide-ozonide complex. The end-on-bonded OBiOOO complex further rearranges to a more stable side-on bonded OBiO3 isomer upon sample annealing. In addition, the bent bismuth dioxide anion is also formed and assigned.

Matrix isolation spectroscopic and theoretical study of water adsorption and hydrolysis on molecular tantalum and niobium oxides.

The reactions of molecular tantalum and niobium monoxides and dioxides with water were investigated by matrix isolation infrared spectroscopy. In solid neon, the metal monoxide and dioxide molecules reacted with water to form the MO(H(2)O) and MO(2)(H(2)O) (M = Ta, Nb) complexes spontaneously on annealing. The MO(H(2)O) complexes photochemically rearranged to the more stable HMO(OH) isomers via one hydrogen atom transfer from water to the metal center under visible light excitation. In contrast, the MO(2)(H(2)O) complexes isomerized to the more stable MO(OH)(2) molecules via a hydrogen atom transfer from water to one of the oxygen atoms of metal dioxide upon visible light irradiation. The aforementioned species were identified by isotopic-substituted experiments as well as density functional calculations.

Formation and characterization of two interconvertible side-on and end-on bonded beryllium ozonide complexes.

The reactions of beryllium atoms with dioxygen were reinvestigated by matrix isolation infrared absorption spectroscopy. Besides the previously reported linear OBeO and cyclic Be(2)O(2) molecules, two interconvertible beryllium ozonide complexes were prepared and characterized. The BeOBe(η(2)-O(3)) complex was formed on annealing, which is characterized to be a side-on bonded ozonide complex with a planar C(2v) structure. The BeOBe(η(2)-O(3)) complex isomerized to the BeOBe(η(1)-O(3)) isomer under visible light excitation, which is an end-on bonded ozonide complex with planar C(s) symmetry. These two isomers are interconvertible; that is, visible light induces the conversion of the side-on bonded complex to the end-on bonded isomer, and vice versa on annealing. In addition, evidence is also presented for the linear BeOBeOBe cluster.

Tantalum dioxide complexes with dinitrogen. formation and characterization of the side-on and end-on bonded TaO2(NN)x (x = 1-3) complexes.

The reaction of tantalum dioxide molecule with dinitrogen has been studied by matrix isolation infrared spectroscopy. The tantalum dioxide molecules produced from laser evaporation of bulk Ta(2)O(5) target reacted with dinitrogen to form the TaO(2)(eta(1)-NN)(x) (x = 1-3) complexes on annealing, in which the N(2) ligands are end-on bonded to the tantalum metal center. The TaO(2)(eta(1)-NN)(3) complex decomposed to TaO(2)(eta(1)-NN)(2) under infrared irradiation. The TaO(2)(eta(1)-NN)(2) and TaO(2)(eta(1)-NN)(3) complexes rearranged to the less stable TaO(2)(eta(1)-NN)(eta(2)-N(2)) and TaO(2)((eta(1)-NN)(2)(eta(2)-N(2)) isomers under visible light excitation. Both the mono- and bis-dinitrogen complexes were predicted to have (2)A' or (2)A(1) ground states arising from the (2)A(1) ground state of TaO(2), whereas the two tridinitrogen complexes were predicted to have (2)B(2) ground states with C(2v) symmetry, which are derived from the (2)B(1) excited state of TaO(2).