Article pubs.acs.org/JPCA
Formation and Infrared Spectroscopic Characterization of Three Oxygen-Rich BiO4 Isomers in Solid Argon Caixia Wang, Mohua Chen, Zhen Hua Li,* and Mingfei Zhou* Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysts and Innovative Materials, Fudan University, Shanghai 200433, China S Supporting Information *
ABSTRACT: 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, [Bi3+(O2−)(O22‑)]. Under UV−visible light irradiation, the Bi(O2)2 complex rearranges to the more stable OBiOOO isomer, an end-on bonded bismuth monoxideozonide 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.
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INTRODUCTION Dioxygen binding and activation at metal centers are of great importance in a wide range of catalytic and biological processes. Metal oxides and dioxygen complexes are potential intermediates or products during oxidation of metal atoms or clusters. Consequently, great effort has been devoted to the preparation and characterization of various metal oxides and dioxygen complexes.1−13 The transition metal atoms with an incompletely filled d-shell are able to form diverse metal− oxygen clusters as molecular oxygen can bind to the metal center in various ways. It has been shown that many transition metal atoms can interact with more than one dioxygen molecule, yielding various oxygen-rich metal−oxygen complexes including side-on or end-on bonded superoxides and peroxides, and mixed oxoperoxides or oxosuperoxides and even oxo-ozonides.14−29 An interesting question is “can the main group metal atoms without open-shell d electrons form similar oxygen-rich complexes?” Compared to transition metal systems, there are much less experimental reports on spectra and structures of oxygen-rich main group metal−oxygen complexes. However, the metal ozonide complexes have been reported for alkali and alkaline earth metals.30−35 It has been shown that Al atoms can bind up to three O2 units, leading to the oxygen-rich tris-superoxo complex Al(O2)3. The species Al(O2)2 was also observed, being a radical (one unpaired electron) featuring D2d symmetry.36 Ga and In atoms react with O2 to give first the cyclic superoxo complex MO2, which photoisomerizes into a linear OMO molecule by UV excitation. Reactions of these dioxide species with a second O2 molecule lead to MO4, an end-on bonded superoxo complex of Ga and In.37,38 Even an oxygen-rich complex was reported for magnesium. A bisozonide complex, Mg(O3)2 with two equivalent side-on bonded ozonide ligands with D2h symmetry was formed via metal atom and dioxygen reactions in solid argon.39 © 2013 American Chemical Society
Here we report a combined matrix isolation infrared spectroscopic and theoretical study of three oxygen-rich BiO4 isomers formed by metal atom and dioxygen reactions in solid argon matrix.
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EXPERIMENTAL AND THEORETICAL METHODS The bismuth−oxygen complexes were prepared by the reactions of bismuth atoms with dioxygen in solid argon. The bismuth atoms were produced by pulsed laser evaporation of metal target. The experimental setup for pulsed laser evaporation and matrix isolation infrared spectroscopic investigation has been described in detail previously.40 Briefly, the 1064 nm fundamental of a Nd:YAG laser (Continuum, Minilite II; 10 Hz repetition rate and 6 ns pulse width) was focused onto a rotating bismuth metal target through a hole in a CsI window cooled normally to 6 K by means of a closedcycle helium refrigerator (ARS, 202N). The laser-evaporated bismuth atoms were codeposited with O2/Ar mixtures onto the CsI window. In general, matrix samples were deposited for 1 h at a rate of approximately 4 mmol/h. The O2/Ar mixtures were prepared in a stainless steel vacuum line using standard manometric technique. O2 (Shanghai BOC, >99.5%), and isotopic-labeled 18O2 (ISOTEC, 99%) were used without further purification. The infrared absorption spectra of the resulting samples were recorded on a Bruker IFS 66 V spectrometer at 0.5 cm−1 resolution between 4000 and 400 cm−1 using a DTGS detector. After the infrared spectrum of the initial deposition had been recorded, the samples were warmed up to a certain temperature (25−35 K), quickly recooled, and more spectra were taken. Selected samples were also subjected Received: June 21, 2013 Revised: October 10, 2013 Published: October 11, 2013 11217
dx.doi.org/10.1021/jp406126c | J. Phys. Chem. A 2013, 117, 11217−11224
The Journal of Physical Chemistry A
Article
to broad band irradiation using a high-pressure mercury arc lamp with glass filters. Quantum chemical calculations were performed to determine the molecular structures and to support the assignment of vibrational frequencies of the observed reaction products. Calculations were performed using the PBE GGA functional with the 6-311+G(2df) basis set for the O atoms and the augcc-pVTZ-PP pseudo potential and basis set for Bi.41−45 Calculations were performed for several possible spin states of the species involved and it was found that the doublet spin state is the ground electronic state for the neutral species. The geometries were fully optimized, and the harmonic vibrational frequencies were calculated with analytic second derivatives. The zero-point energies (ZPE) were derived. The PBE functional and the basis sets employed in the present study well reproduced the experimental fundamental vibrational frequency of the O2 molecule (1552.2 cm−1 (PBE) vs 1556.2 (Expt.)),46 and thus no scaling factor was applied to the theoretical harmonic vibrational frequencies. Transition state optimizations were done with the synchronous transit-guided quasi-Newton (STQN) method and were verified through intrinsic reaction coordinate (IRC) calculations. All the calculations were performed by using the Gaussian 09 program.47
Figure 2. Infrared spectra in the 1360−1020 cm−1 region from codeposition of laser-evaporated bismuth atoms with 0.1% O2 in argon: (a) after 1 h of sample deposition at 6 K, (b) after annealing to 30 K, (c) after 15 min of visible light irradiation (λ> 500 nm), (d) after 15 min of 250 nm
