Density Functional Theoretical Studies of the Re−Xe Bonds in Re(Cp)(CO)(PF3)Xe and Re(Cp)(CO)2Xe

Noble Gas-Tungsten Peroxide Complexes in Noble Gas Matrixes: Infrared Spectroscopy and Density Functional Theoretical Study

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that tungsten oxo and mono-superoxide, WO₃ and (η²-O₂)WO₂, coordinate noble gas atoms in forming noble gas-tungsten oxide complexes. The results showed that both WO₃ and (η²-O₂)WO₂ oxides can coordinate one Ar or Xe atom in solid noble gas matrixes; otherwise, tungsten mono- and dioxides cannot. Hence, the WO₃ and (η²-O₂)WO₂ molecules trapped previously in solid argon noble gas matrixes should be regarded as the WO₃(Ar) oxide and (η²-O₂)WO₂(Ar) peroxide complexes. When annealing, the lighter Ar atom can be replaced by a heavier xenon atom to form WO₃(Xe) and (η²-O₂)WO₂(Xe) complexes. What's more, upon UV photolysis, both Ar and Xe atoms can be replaced by oxygen to form a tungsten disuperoxide (η²-O₂)₂WO₂ complex. The binding energies were predicted to be 25.7, 16.6, 9.4, 14.7, and 8.1 kcal/mol for the (η²-O₂)₂WO₂, WO₃(Xe), WO₃(Ar), (η²-O₂)WO₂(Xe), and (η²-O₂)WO₂(Ar) complexes at the CCSD(T)//M06-2X-D3//def2-TZVP/DGDZVP/SDD level. The substitution law, O₂ > Xe > Ar, can be interpreted according to the chemical reaction energies calculated to be -6.6 and +11.0 kcal/mol, respectively, for the equation formulas Xe + (η²-O₂)WO₂(Ar) = (η²-O₂)WO₂(Xe) + Ar and O₂ + (η²-O₂)WO₂(Xe) = (η²-O₂)₂WO₂ + Xe at the same level.

Contrasting Behavior of the Z Bonds in X-Z···Y Weak Interactions: Z = Main Group Elements Versus the Transition Metals

In contrast to the increasing family of weak intermolecular interactions in main-group compounds (X-Z···Y, Z = main-group elements), an analysis of the Cambridge Structural Database indicates that electron-saturated (18-electron) transition-metal complexes show reluctance toward weak M bond formation (X-M···Y, M = transition metal). In particular, weak M bonds involving electron-saturated (18-electron) complexes of transition metals with partially filled d-orbitals are not found. We propose that the nature of valence electron density distribution in transition-metal complexes is the primary reason for this reluctance. A survey of the interaction of selected electron-saturated transition-metal complexes with electron-rich molecules (Y) demonstrates the following: shielding the possible σ-hole on the metal center by the core electron density in 3d series, and enhanced electronegativity and relativistic effects in 4d and 5d series, hinders the formation of the M bond. A balance in all the destabilizing effects has been found in the 4d series due to its moderate polarizability and primogenic repulsion from inner core d-electrons. A changeover in the donor-acceptor nature of the metal center toward different types of incoming molecules is also unveiled here. The present study confirms the possibility of M bond as a new supramolecular force in designing the crystal structures of electron-saturated transition-metal complexes by invoking extreme ligand conditions.

Basis set effects in simple compounds of heavy rare gases

Rare-gas hydrides of the type HRgX (Rg = Xe or Rn and X = F, Cl, Br, or I) have been studied using Møller–Plesset and density functional theory methods. Six model core potentials and their associated basis sets were used, with relativistic effects included implicitly. The effects of polarization, correlating, and diffuse basis functions were investigated. Molecular geometries of the metastable hydrides and transition states along the decomposition pathway were computed together with corresponding energies of formation and decomposition. The results of quantum theory of atoms in molecules analysis further elucidate the interactions between atoms in HRgX species and confirm the results of analyses obtained from the natural bond orbitals approach.

A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF3)] studied with NMR and time-resolved IR spectroscopy

The organometallic alkane complexes Re(Cp)(CO)(PF(3))(alkane) and Re(Cp)(CO)(2)(alkane) have been detected after the photolysis of Re(Cp)(CO)(2)(PF(3)) in alkane solvent. NMR and time-resolved IR experiments reveal that the species produced by the interaction of n-pentane with [Re(Cp)(CO)(PF(3))] are an equilibrium mixture of Re(Cp)(CO)(PF(3))(pentane) and Re(Cp)(CO)(PF(3))(pentyl)H. The interaction of cyclopentane with [Re(Cp)(CO)(PF(3))] most likely results in a similar equilibrium between cyclopentyl hydride and cyclopentane complexes. An increasing proportion of alkane complex is observed on going from n-pentane to cyclopentane to cyclohexane, where only a small amount, if any, of the cyclohexyl hydride form is present. In general, when [Re(Cp)(CO)(PF(3))] reacts with alkanes, the products display a higher degree of oxidative cleavage in comparison with [Re(Cp)(CO)(2)], which favors alkane complexation without activation. Species with the formula Re(Cp)(CO)(PF(3))(alkane) have higher thermal stability and lower reactivity toward CO than the analogous Re(Cp)(CO)(2)(alkane) complexes.

Solid-State 129Xe and 131Xe NMR Study of the Perxenate Anion XeO64-

Results of the first solid-state 131Xe NMR study of xenon-containing compounds are presented. The two NMR-active isotopes of xenon, 129Xe (I=1/2) and 131Xe (I=3/2), are exploited to characterize the xenon magnetic shielding and quadrupolar interactions for two sodium perxenate salts, Na4XeO6.xH2O (x=0, 2), at an applied magnetic field strength of 11.75 T. Solid-state 129/131Xe NMR line shapes indicate that the local xenon environment in anhydrous Na4XeO6 adopts octahedral symmetry, but upon hydration, the XeO6(4-) anion becomes noticeably distorted from octahedral symmetry. For stationary, anhydrous samples of Na4XeO6, the heteronuclear 129/131Xe-23Na dipolar interaction is the principal contributor to the breadth of the 129/131Xe NMR lines. For stationary and slow magic-angle-spinning samples of Na4XeO(6).2H2O, the anisotropic xenon shielding interaction dominates the 129Xe NMR line shape, whereas the 131Xe NMR line shape is completely dominated by the nuclear quadrupolar interaction. The xenon shielding tensor is approximately axially symmetric, with a skew of -0.7+/-0.3, an isotropic xenon chemical shift of -725.6+/-1.0 ppm, and a span of 95+/-5 ppm. The 131Xe quadrupolar coupling constant, 10.8+/-0.5 MHz, is large for a nucleus at a site of approximate Oh symmetry, and the quadrupolar asymmetry parameter indicates a lack of axial symmetry. This study demonstrates the extreme sensitivity of the 131Xe nuclear quadrupolar interaction to changes in the local xenon environment.