Mohua Chen

Matrix-isolation infrared spectroscopic studies on ablated products generated from laser ablation of Ta2O5 and Ta in ambient O2/Ar gas

Abstract Using matrix-isolation infrared spectroscopy, 532 nm pulsed laser ablation of Ta2O5 and Ta targets in O2/Ar gas ambient has been investigated. The major ablated products of the tantalum-containing oxides were found to be the neutrals TaO, TaO2, (O2)TaO2, and the anions TaO2−, TaO3−, as well as cations TaO+, TaO2+ in minority. The observed infrared absorptions of these tantalum-containing oxides were reproduced by DFT calculations of vibrational fundamentals. The formation reaction channels of these products during the laser ablation process have been discussed.

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.

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.

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.

Reactions of titanium oxides with water molecules. A matrix isolation FTIR and density functional study

Reactions of titanium dioxides with water molecules have been studied by matrix isolation infrared and density functional theoretical calculations. In solid argon, titanium dioxide molecules reacted with water to form OTi(OH)2 molecules spontaneously on annealing. The potential energy surface along the TiO2+H2O→OTi(OH)2 reaction path was calculated. Although titanium dioxide–water complex was predicted to be stable, this complex was not observed due to low energy barrier and high exothermicity for the hydrolysis reaction. Evidence is also presented for the formation of OTi–OH2 complex.

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.

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 ](+) .

Rare-earth monocarbonyls MCO: comprehensive infrared observations and a transparent theoretical interpretation for M = Sc; Y; La–Lu

The reactions of Group-3 metal atoms with carbon monoxide in solid argon have been studied using matrix isolation infrared absorption spectroscopy. The lanthanide monocarbonyls LnCO were produced spontaneously on annealing. The observations on LnCO, Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, and Er are new. We also theoretically study the structure, bonding, and C–O stretch infrared frequencies. The covalent M–C bonding contains both M ← C σ donation from the carbon lone pair, and M 5d → CO 2π* back donation contributions. In addition to the open 4fn shells, the total spin, as found earlier, may have contributions from an M ‘σ doughnut’ and the M–C π bond, in a σ1π1, σ1π2 high-spin, or σ2π1 low-spin configuration. They form at least a single-bond, and those with the σ1π2 configuration approach a double bond in length. The weakening of the C–O bonding is related to the back donation to the antibonding C–O 2π* orbital.

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.

Activation of CO2 by Zr atom. Matrix-isolation FTIR spectroscopy and density functional studies

Abstract Combined experimental and theoretical studies have been performed for examining the interaction between Zr atom and CO 2 . Matrix-isolation FTIR spectra reveal that OZrCO is the main reaction product of laser-ablated Zr with CO 2 , identified by IR bands at 1837.8 and 878.9 cm −1 , correlating to the C–O and Zr–O stretching modes, respectively. Density functional calculations at the B3LYP level have been used to characterize the formation channel of the insertion product OZrCO. We have found that interaction of ground state Zr atom (4d 2 5s 2 ) with CO 2 on the triplet energy surface leads eventually to the insertion product OZrCO and the process is barrierless, indicating that activation of CO 2 by Zr atom requires no energy input. The theoretical results are consistent with the experimental observations.