Lester Andrews

Spectroscopic and Theoretical Studies of Transition Metal Oxides and Dioxygen Complexes

3.1. Sc Group 6772 3.2. Ti Group 6773 3.3. V Group 6775 3.4. Cr Group 6776 3.5. Mn Group 6777 3.6. Fe Group 6779 3.7. Co Group 6780 3.8. Ni Group 6782 3.9. Cu Group 6782 3.10. Zn Group 6784 3.11. Lanthanide Group 6784 3.12. Actinide Group 6785 3.13. Periodic Trends on Bonding and Reactivity 6785 4. Ionic Mononuclear Transition Metal Oxide Species 6787 4.1. Cations 6788 4.2. Anions 6790 4.2.1. Monoxide Anions 6790 4.2.2. Dioxide Anions 6791 4.2.3. Oxygen-Rich Anions 6792 5. Multinuclear Transition Metal Oxide Clusters 6792 5.1. Sc Group 6793 5.2. Ti Group 6793 5.3. V Group 6793 5.4. Cr Group 6797 5.5. Mn Group 6798 5.6. Fe Group 6798 5.7. Co Group 6798 5.8. Ni Group 6798 5.9. Cu Group 6799 6. Summary 6800 7. Acknowledgments 6800 8. References 6800

Reactions of boron atoms with molecular oxygen. Infrared spectra of BO, BO2, B2O2, B2O3, and BO−2 in solid argon

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.

Matrix infrared spectra and density functional calculations of transition metal hydrides and dihydrogen complexes.

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 MH(2) or M(H(2)) molecules so formed react further to form higher MH(4), (H(2))MH(2), or M(H(2))(2), and MH(6), (H(2))(2)MH(2), or M(H(2))(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.

Infrared Spectrum, Structure, Vibrational Potential Function, and Bonding in the Lithium Superoxide Molecule LiO2

Lithium superoxide has been synthesized by reacting lithium atoms and oxygen molecules at high dilution in inert and oxygen matrices. Isotopic substitution at all atomic positions and use of isotopic mixtures verify the molecular identity and indicate an isosceles triangular structure. Eighteen frequencies from six isotopic molecules determine the potential constants FO–O = 5.59 ± 0.05, FLi–O = 1.18 ± 0.02, and FLi–O,Li–O = − 0.21 ± 0.03 mdyn / A. The oxygen–oxygen force constant for LiO2 coincides with that calculated for O2−, which suggests that the LiO2 molecule is highly ionic and may be considered as a lithium cation bonded to a superoxide anion by Coulombic forces.

INFRARED SPECTRUM OF THE DIFLUOROMETHYL RADICAL IN SOLID ARGON.

When HCBrF2 and DCBrF2 at high dilution in argon are codeposited with an atomic beam of lithium on a CsI window at 15°K, lithium bromide absorptions appear along with several new absorptions not present when the precursor was deposited without alkali metal. These new absorptions are assigned to the antisymmetric hydrogen bending and carbon–fluorine stretching modes and the symmetric C–F vibration of the HCF2 and DCF2 radicals. The antisymmetric vibrational assignments are supported by product rule and normal coordinate calculations which give the potential constants F55 = 5.27 ± 0.1 mdyn/A, F56 = 0.44 ± 0.02 mdyn/rad, and F66 = 0.64 ± 0.05 mdyn·A/rad2. An approximate force constant F22 = 7.19 ± 0.7 mdyn/A is calculated from the symmetric C–F vibration. The carbon–fluorine valence force constant for HCF2 is in the range of those for typical fluorocarbons.

Matrix Reactions of K and Rb Atoms with Oxygen Molecules

Deposition of atomic beams of potassium and rubidium with oxygen molecules at high dilution in argon together on a salt window at 15°K produces the KO2 and RbO2 molecules, as identified by infrared spectra. Secondary reaction yields the KO2K and RbO2Rb molecules. Oxygen isotopic mixtures and simultaneous deposition of two different alkali‐metal atoms verify the molecular composition. Detailed concentration changes and oxygen isotropic mixtures identify the new molecular species O2KO2 and O2RbO2, the potassium and rubdium disuperoxide molecules which likely have the D2d structure. Force constants for the molecules synthesized here are compared with those reported earlier for LiO2 and NaO2.

Argon matrix infrared spectra and vibrational analysis of the hydroperoxyl and deuteroperoxyl free radicals

Matrix reactions of H and D atoms from a microwave discharge source with oxygen molecules diluted in argon have produced significantly higher yields of HO2 and DO2 than the previous photolysis methods. Oxygen isotopic enrichment confirmed the previous vibrational assignments to HO2; significantly greater concentrations of DO2 allowed observation of the weak 0–0 mode at 1123 cm−1. Normal coordinate calculations using HO2 and DO2 oxygen isotopic frequencies gave excellent agreement with the observed data. The bonding in HO2 is suggested to be largely covalent, in contrast to the ionic species Li+O2−.

Polyfluoride anions, a matrix-isolation and quantum-chemical investigation.

Laser-ablation experiments with metals provide a source of electrons for capture processes, which are codeposited with solid argon and neon containing molecular fluorine. New argon and neon matrix absorptions at 510.6 and 524.7 cm(-1), respectively, are photosensitive upon irradiation at >290 nm, which is consistent with their assignment to an isolated anion. These bands are below the [M](+)[F(3)](-) antisymmetric trifluoride stretching frequency of 550 cm(-1) in an argon matrix, which is the typical relationship for cation-anion complexes and matrix-isolated anions. Thus, we report the isolated [F(3)](-) anion in solid argon and neon environments. Moreover, we have carried out quantum-chemical calculations up to and including the CCSD(T) method to investigate the stabilities of polyfluoride anions higher than the [F(3)](-) anion.

Raman Spectra of the Products of Na and K Atom Argon Matrix Reactions with O2 Molecules

Raman spectra of samples of sodium and potassium atoms codeposited at 16°K with oxygen molecules at high dilution in argon showed strong bands at 1094 and 1108 cm−1, respectively, which are assigned to the superoxide fundamentals in the Na+O2− and K+O2− molecules. These features were split into triplets using 16O2, 16O18O, 18O2 samples, which indicates isosceles triangular structures; absence of M+–O2− interionic modes confirms the ionic model for the alkali superoxide molecules. Infrared bands at 1079 and 1097–1104 cm−1 in Na and K atom −O2 reactions, respectively, are assigned to the dimeric species (M+O2−)2. The symmetric metal‐oxygen mode for O2KO2 was observed in the Raman at 305 cm−1, inferring more covalent character in the metal oxygen bonding in this species than in the alkali superoxides.

On microwave discharge sources of new chemical species for matrix‐isolation spectroscopy and the identification of charged species

The mechanism for trapping new chemical species by condensing the products of a microwave discharge with inert matrices has been investigated. Variation of geometrical, electrical, and chemical parameters of the Ar, HCl, Cl2 system indicated that the major product species—HCl2 radical or anion—was formed under conditions where neither ions nor atomic species produced in the discharge were condensed in the matrix. The mechanism for forming the product species is vacuum ultraviolet photolysis of the sample during deposition with radiation from the microwave discharge, since a coaxial orifice discharge tube provided photolysis and produced the product species, while studies with an off‐axis orifice discharge tube, which could not serve as a photolysis source, did not produce the product. The H atom–Cl2 reaction gave HCl using both discharge tubes, but the HClx2 species was produced only with the coaxial tube. Hence, this species requires vacuum ultraviolet light in addition to H and Cl atoms for its producti...