Reactions of boron atoms with molecular oxygen. Infrared spectra of BO, BO2, B2O2, B2O3, and BO−2 in solid argon
15 Dec 1991-Journal of Chemical Physics (American Institute of Physics)-Vol. 95, Iss: 12, pp 8697-8709
TL;DR: In this article, the product infrared spectrum was dominated by three strong 11B isotopic bands at 1299.3, 1282.8, and 1274.6 cm−1 with 10B counterparts at 1347.6, 1330.7, and 1322.2 cm− 1.
Abstract: Boron atoms from Nd:YAG laserablation of the solid have been codeposited with Ar/O2 samples on a 11±1 K salt window. The product infrared spectrum was dominated by three strong 11B isotopic bands at 1299.3, 1282.8, and 1274.6 cm− 1 with 10B counterparts at 1347.6, 1330.7, and 1322.2 cm− 1. Oxygen isotopic substitution (16O18O and 18O2 ) confirms the assignment of these strong bands to ν3 of linear BO2. Renner–Teller coupling is evident in the ν2 bending motion. A sharp medium intensity band at 1854.7 has appropriate isotopic ratios for BO, which exhibits a 1862.1 cm− 1 gas phase fundamental. A sharp 1931.0 cm− 1 band shows isotopic ratios appropriate for another linear BO2 species; correlation with spectra of BO− 2 in alkali halide lattices confirms this assignment. A weak 1898.9 cm− 1 band grows on annealing and shows isotopic ratios for a BO stretching mode and isotopic splittings for two equivalent B and O atoms, which confirms assignment to B2O2. A weak 2062 cm− 1 band grows markedly on annealing and shows isotope shifts appropriate for a terminal–BO group interacting with another oxygen atom; the 2062 cm− 1 band is assigned to B2O3 in agreement with earlier work. A strong 1512.3 cm− 1 band appeared on annealing; its proximity to the O2 fundamental at 1552 cm− 1 and pure oxygen isotopic shift suggest that this absorption is due to a B atom–O2 complex.
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TL;DR: The laser-ablation method produces mostly neutral atoms with a few percent cations and electrons for capture to make anions; in contrast, thermal evaporation gives only neutral species, so the very recent neon matrix investigations in the laboratory provide carbonyl cation and anions for comparison to neutrals on a level playing field.
Abstract: Figure 18 presents the C-O stretching vibrational frequencies of the first-row transition-metal monocarbonyl cations, neutrals, and anions in solid neon; similar diagrams have been reported for neutral MCO species in solid argon, but three of the early assignments have been changed by recent work and one new assignment added. The laser-ablation method produces mostly neutral atoms with a few percent cations and electrons for capture to make anions; in contrast, thermal evaporation gives only neutral species. Hence, the very recent neon matrix investigations in our laboratory provide carbonyl cations and anions for comparison to neutrals on a level playing field. Several trends are very interesting. First, for all metals, the C-O stretching frequencies follow the order cations > neutrals > anions with large diagnostic 100-200 cm-1 separations, which is consistent with the magnitude of the metal d to CO pi * donation. Second, for a given charge, there is a general increase in C-O stretching vibrational frequencies with increasing metal atomic number, which demonstrates the expected decrease in the metal to CO pi * donation with increasing metal ionization potential. Some of the structure in this plot arises from the extra stability of the filled and half-filled d shell and from the electron pairing that occurs at the middle of the TM row; the plot resembles the "double-humped" graph found for the variation in properties across a row of transition metals. For the anions, the variation with metal atom is the smallest since all of the metals can easily donate charge to the CO ligand. Third, for the early transition-metal Ti, V, and Cr families, the C-O stretching frequencies decrease when going down the family, but the reverse relationship is observed for the late transition-metal Fe, Co, and Ni families. In most of the present discussion, we have referred to neon matrix frequencies; however, the argon matrix frequencies are complementary, and useful information can be obtained from comparison of the two matrix hosts. In most cases, the neon-to-argon red shift for neutral carbonyls is from 11 to 26 cm-1, but a few (CrCO) lie outside of this range. In the case of FeCO and Fe(CO)2, it appears that neon and argon trap different low-lying electronic states. In general, the carbonyl neutrals and anions have similar shifts but carbonyl cations have larger matrix shifts. For example, the FeCO+ fundamental is at 2123.0 cm-1 in neon and 2081.5 cm-1 in argon, a 42.5 cm-1 shift, which is larger than those found for FeCO- (11.7 cm-1) and FeCO (11.7 cm-1). It is unusual for different low-lying electronic states to be trapped in different matrices, but CUO provides another example. The linear singlet state (1047.3, 872.2 cm-1) is trapped in solid neon, and a calculated 1.2 kcal/mol higher triplet state is trapped in solid argon (852.5, 804.3 cm-1) and stabilized by a specific interaction with argon. The bonding trends are well described by theoretical calculations of vibrational frequencies. Table 5 compares the scale factors (observed neon matrix/calculated) for the C-O stretching modes of the monocarbonyl cations, neutrals, and anions of the first-row transition metals observed in a neon matrix using the B3LYP and BP86 density functionals. Most of the calculated carbonyl harmonic stretching frequencies are within 1% of the experimental fundamentals at the BP86 level of theory, while calculations using the B3LYP functional give frequencies that are 3-4% higher as expected for these density functionals and calculations on saturated TM-carbonyls. For second- and third-row carbonyls using the BP86 density functional and the LANL effective core potential in conjunction with the DZ basis set, the agreement between theory and experiment is just as good. For example, the 16 M(CO)1-4 neutral and anion and 2 MCO+ cation (M = Ru, Os) carbonyl frequencies are fit within 1.5%. The 16 species (M = Rh, Ir) are fit within 1%, but the Rh(CO)1-4+ calculations are 2-3% too low and Ir(CO)1-4+ computations are 1-2% too low. In addition to predicting the vibrational frequencies, DFT can be used to calculate different isotopic frequencies, and isotopic frequency ratios can be computed as a measure of the normal vibrational mode in the molecule for an additional diagnostic. For diatomic CO, the 12CO/13CO ratio 1.0225 and C16O/C18O ratio 1.0244 characterize a pure C-O stretching mode. In a series of molecules such as RhCO+, RhCO, and RhCO-, where the metal-CO bonding varies, the Rh-C, C-O vibrational interaction is different and the unique isotopic ratios for the carbonyl vibration are characteristic of that particular molecule. Table 6 summarizes the isotopic ratios observed and calculated for the RhCO+,0,- species. Note that RhCO+ exhibits slightly more carbon-13 and less oxygen-18 involvement in the C-O vibration than CO itself and that this trend increases to RhCO and to RhCO- as the Rh-C bond becomes shorter and stronger. Note also how closely the calculated and observed ratios both follow this trend. In a molecule with two C-O stretching modes, for example, bent Ni(CO)2 exhibits a strong b2 mode at 1978.9 cm-1 and a weak a1 mode at 2089.7 cm-1 in solid neon, and these two modes involve different C and O participations. The symmetric mode shows substantially more C (1.0242) and less O (1.0217) participation than does the antisymmetric mode with C (1.0228) and O (1.0238) involvement, based on the given isotopic frequency ratios, which are nicely matched by DFT calculations (a1 1.0244, 1.0224 and b2 1.0232, 1.0241, respectively). These investigations of vibrational frequencies in unsaturated transition-metal carbonyl cations, neutrals, and anions clearly demonstrate the value of a close working relationship between experiment and theory to identify and characterize new molecular species.
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TL;DR: Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate.
Abstract: Metal hydrides are of considerable importance in chemical synthesis as intermediates in catalytic hydrogenation reactions. Transition metal atoms react with dihydrogen to produce metal dihydrides or dihydrogen complexes and these may be trapped in solid matrix samples for infrared spectroscopic study. The MH2 or M(H2) molecules so formed react further to form higher MH4, (H2)MH2, or M(H2)2, and MH6, (H2)2MH2, or M(H2)3 hydrides or complexes depending on the metal. In this critical review these transition metal and dihydrogen reaction products are surveyed for Groups 3 though 12 and the contrasting behaviour in Groups 6 and 10 is discussed. Minimum energy structures and vibrational frequencies predicted by Density Functional Theory agree with the experimental results, strongly supporting the identification of novel binary transition metal hydride species, which the matrix-isolation method is well-suited to investigate. 104 references are cited.
297 citations
TL;DR: The synthesis of atomically thin 2D γ-boron films on copper foils is achieved by chemical vapor deposition using a mixture of pure boron andboron oxide powders as the borons source and hydrogen gas as the carrier gas.
Abstract: Two-dimensional boron materials have recently attracted extensive theoretical interest because of their exceptional structural complexity and remarkable physical and chemical properties. However, such 2D boron monolayers have still not been synthesized. In this report, the synthesis of atomically thin 2D γ-boron films on copper foils is achieved by chemical vapor deposition using a mixture of pure boron and boron oxide powders as the boron source and hydrogen gas as the carrier gas. Strikingly, the optical band gap of the boron film was measured to be around 2.25 eV, which is close to the value (2.07 eV) determined by first-principles calculations, suggesting that the γ-B28 monolayer is a fascinating direct band gap semiconductor. Furthermore, a strong photoluminescence emission band was observed at approximately 626 nm, which is again due to the direct band gap. This study could pave the way for applications of two-dimensional boron materials in electronic and photonic devices.
232 citations
TL;DR: 1. Electron Spin Resonance 2116 2. Infrared and Optical Absorption 2117 3. Laser-Induced Fluorescence 2119 II.
Abstract: 1. Electron Spin Resonance 2116 2. Infrared and Optical Absorption 2117 3. Laser-Induced Fluorescence 2119 III. Quantum Hosts 2122 IV. Matrix Isolation Spectroscopy of Molecular Ions 2124 A. Ion Sources for Matrix Isolation Spectroscopy 2124 B. Spectroscopic Methods 2126 1. Electron Spin Resonance 2126 2. Infrared and Optical Absorption 2126 3. Laser-Induced Fluorescence 2127 V. Deposition of Mass-Selected Species 2128 VI. Summary 2130
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References
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TL;DR: In this article, the vapor above heated lithium oxide (Li2O) has been investigated mass spectrometrically and by infrared matrix-isolation spectroscopy and the vapor composition and Knudsen effusion rates were measured as functions of temperature, and the matrix spectra of the principal lithium oxide species were identified and analyzed for different isotopic abundances.
Abstract: The vapor above heated lithium oxide (Li2O) has been investigated mass spectrometrically and by infrared matrix‐isolation spectroscopy. The vapor composition and Knudsen effusion rates were measured as functions of temperature, and the matrix spectra of the principal lithium oxide species—Li2O, LiO, Li2O2—identified and analyzed for different isotopic abundances. The predominant vapor species Li72O is probably linear with r(Li–O) = 1.59 A, and has fundamentals ν1, ν2, ν3 at [760], [140], and 987 cm—1, respectively. Its heat of formation ΔH0°(f) = —43.7±2.5 kcal/mole. The diatomic molecule Li7O has ν = 745 cm—1, an estimated bond length r = 1.62 A, and ΔH0°(f) = +16.0±5 kcal/mole. The previously undetected molecule Li72O2 is shown to resemble the alkali halide dimers in having a planar rhombic (Vh) structure for which the O–Li–O angle and Li–O bond length are estimated to be 116° and 1.90 A, respectively. Its B2u and B3u frequencies are found at 324 and 522 cm—1, respectively, in a krypton matrix. The rema...
152 citations
145 citations
TL;DR: The boron flame bands have been observed in absorption during the flash photolysis of mixtures of Boron trichloride and oxygen and detailed analysis of the spectrum has shown that the bands arise from...
Abstract: The boron flame bands have been observed in absorption during the flash photolysis of mixtures of boron trichloride and oxygen. Detailed analysis of the spectrum has shown that the bands arise from...
123 citations
TL;DR: In this paper, the infrared spectra of B2O3 and BO2 isolated in solid argon matrices have been investigated in the region 350-4000 cm-1.
Abstract: The infrared absorption spectra of B2O3, B2O2, and BO2 isolated in solid argon matrices have been investigated in the region 350–4000 cm—1. The visible absorption spectrum of matrix‐isolated BO2 was observed in the region 4000–5500 A. The gaseous species were generated in a high‐temperature effusion cell and trapped under conditions of moderate to high dilution in solid argon matrices at approximately 4°K. Bands were found at 1955, 1921, 1899, 1323, and 1276 cm—1 in the infrared spectra of B210O2, B10B11O2, B211O2, and B10O2, and B11O2, respectively. For both B210O3 and B211O3 infrared spectra of the most dilute matrices show seven distinct bands in the region 450–2100 cm—1. Six of these can be readily assigned as fundamentals and their relative intensities explained if the known ``V'' structure of B2O3 is supposed to have a larger apex angle than that determined by electron diffraction, and the correlation of the normal vibrations and selection rules with those for the linear symmetric (D∞h) model is con...
113 citations
TL;DR: The 15°K deposition of alkali metal atoms and ozone molecules at high dilution in argon produced very intense bands near 800 cm−1 and weak bands near 600 cm− 1 which showed appropriate oxygen isotopic shifts for assignment to v3 and v2 of the ozonide ion as mentioned in this paper.
Abstract: The 15°K deposition of alkali metal atoms and ozone molecules at high dilution in argon produced very intense bands near 800 cm−1 and weak bands near 600 cm−1 which showed appropriate oxygen isotopic shifts for assignment to v3 and v2 of the ozonide ion. Energetic considerations and alkali metal effects clearly indicated bonding of the metal cation to the ozonide anion. The use of scrambled isotopic ozones showed that the metal cation was symmetrically bound to the ozonide anion in a C2v structure; the symmetric interionic stretching mode was observed at 281 cm−1 for Cs+O3−. The cesium‐ozone reaction produced argon matrix fundamentals for CsO at 322 cm−1 and Cs2O at 457 cm−1; simultaneous mercury arc photolysis was required to yield the LiO absorption at 752 cm−1 from the lithium‐ozone argon matrix reaction.
94 citations