Noble gas-actinide compounds: complexation of the CUO molecule by Ar, Kr, and Xe atoms in noble gas matrices

Reaction of Laser-Ablated Uranium and Thorium Atoms with H2Se: A Rare Example of Selenium Multiple Bonding

The compounds H2ThSe and H2USe were synthesized by the reaction of laser-ablated actinide metal atoms with H2Se under cryogenic conditions following the procedures used to synthesize H2AnX (An = Th, U; X = O, S). The molecules were characterized by infrared spectra in an argon matrix with the aid of deuterium substitution and electronic structure calculations at the density functional theory level. The main products, H2ThSe and H2USe, are shown to have a highly polarized actinide-selenium triple bond, as found for H2AnS on the basis of electronic structure calculations. There is an even larger back-bonding of the Se with the An than found for the corresponding sulfur compounds. These molecules are of special interest as rare examples of multiple bonding of selenium to a metal, particularly an actinide metal.

The Renaissance of Non-Aqueous Uranium Chemistry

Prior to the year 2000, non-aqueous uranium chemistry mainly involved metallocene and classical alkyl, amide, or alkoxide compounds as well as established carbene, imido, and oxo derivatives. Since then, there has been a resurgence of the area, and dramatic developments of supporting ligands and multiply bonded ligand types, small-molecule activation, and magnetism have been reported. This Review 1) introduces the reader to some of the specialist theories of the area, 2) covers all-important starting materials, 3) surveys contemporary ligand classes installed at uranium, including alkyl, aryl, arene, carbene, amide, imide, nitride, alkoxide, aryloxide, and oxo compounds, 4) describes advances in the area of single-molecule magnetism, and 5) summarizes the coordination and activation of small molecules, including carbon monoxide, carbon dioxide, nitric oxide, dinitrogen, white phosphorus, and alkanes.

Flexible bonding between copper and nitric oxide: infrared photodissociation spectroscopy of copper nitrosyl cation complexes: [Cu(NO)n]+ (n = 1-5)

The infrared spectra of mass-selected mononuclear copper nitrosyl cation complexes [Cu(NO)n](+) with n = 1-5 and their argon tagged complexes are measured via infrared photodissociation spectroscopy in the nitrosyl stretching frequency region in the gas phase. The experimental spectra provide distinctive patterns allowing the determination of the geometries and electronic structures of these complexes by comparison with the predicted spectra from density functional theory computations. The argon tagged [Cu(NO)2Ar2](+) and [Cu(NO)3Ar](+) complexes as well as the higher n = 4 and 5 complexes each involve a bidentate (NO)2 dimer ligand, suggesting that ligand-ligand coupling plays an important role in the bonding of these cation systems. The results also show that argon tagging has a strong influence on the geometric and electronic structures of the n = 2 and 3 complexes. The [Cu(NO)4](+) cation is the most intense peak in the mass spectrum, which is characterized to be the fully coordinated ion with a D2d structure involving two (NO)2 units but with only 14-valence electrons on Cu. The [Cu(NO)5](+) cation complex is determined to involve a [Cu(NO)4](+) core ion that is coordinated by an external NO ligand.

Metastable behavior of noble gas inserted tin and lead fluorides

The metastable FNgEF and FNgEF₃ (E = Sn, Pb; Ng = Kr–Rn) are the first reported neutral compounds possessing Ng–Sn and Ng–Pb covalent bonds.

On the stability of noble gas bound 1-tris(pyrazolyl)borate beryllium and magnesium complexes

1-Tris(pyrazolyl)borate beryllium and magnesium cationic complexes are found to bind Ar–Rn atoms quite effectively.

Singlet ground state actinide chemistry with geminals

We present the first application of the variationally orbital optimized antisymmetric product of 1-reference orbital geminals (vOO-AP1roG) method to singlet-state actinide chemistry.

Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of EUX3 (E=N, P, CH; X=H, F, Cl)

Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-L<TPSS<BLYP<revPBE<BP86<PBE≈PW91. The orbital interactions ΔEorb, in all studied compounds [EUX3] are larger than the electrostatic interaction ΔEelstat, which means the UN bonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The UE σ-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [PUX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme's D3(BJ) corrections, the Corminboeuf's dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals.

Predicted organic compounds derived from rare gas atoms and formic acid

Organic insertion compounds of rare gas atoms into formic acid were investigated at the MP2(full)/aug-cc-pVTZ level. There are two configuration isomers for each molecule based on the location of H atoms: trans- and cis-HCOORgH (Rg = Ar, Kr, Xe). Their structures, harmonic frequencies, and decomposition energies have been calculated using the above ab initio method. Using trans-HCOOXeH as an example, natural bond orbital (NBO) and atom-in-molecules (AIM) analyses were also carried out to explore the binding nature of the rare gas atoms. The formation mechanism of molecular orbitals is also presented in this paper. The presented results indicate that HCOOXeH and HCOOKrH are potential candidates for experimental observation.

Theoretical prediction of XRgCO(+) ions (X = F, Cl, and Rg = Ar, Kr, Xe)

In this work we have predicted novel rare gas containing cationic molecules, XRgCO(+) (X = F, Cl and Rg = Ar, Kr, Xe) using ab initio quantum chemical methods. Detail structural, stability, vibrational frequency, and charge distribution values are reported using density functional theory, second-order Møller-Plesset perturbation theory, and coupled-cluster theory based methods. These ions are found to be metastable in nature and exhibit a linear geometry with C∞v symmetry in their minima energy structures, and the nonlinear transition state geometries are associated with Cs symmetry. Except for the two-body dissociation channel (Rg + XCO(+)), these ions are stable with respect to all other dissociation channels. However, the connecting transition states between the above-mentioned two-body dissociation channel products and the predicted ions are associated with sufficient energy barriers, which restricts the metastable species to transform into the global minimum products. Thus, it may be possible to detect and characterize these metastable ions using an electron bombardment technique under cryogenic conditions.

In quest of strong Be-Ng bonds among the neutral Ng-Be complexes

The global minimum geometries of BeCN2 and BeNBO are linear BeN-CN and BeN-BO, respectively. The Be center of BeCN2 binds He with the highest Be-He dissociation energy among the studied neutral He-Be complexes. In addition, BeCN2 can be further tuned as a better noble gas trapper by attaching it with any electron-withdrawing group. Taking BeO, BeS, BeNH, BeNBO, and BeCN2 systems, the study at the CCSD(T)/def2-TZVP level of theory also shows that both BeCN2 and BeNBO systems have higher noble gas binding ability than those related reported systems. ΔG values for the formation of NgBeCN2/NgBeNBO (Ng = Ar-Rn) are negative at room temperature (298 K), whereas the same becomes negative at low temperature for Ng = He and Ne. The polarization plus the charge transfer is the dominating term in the interaction energy.

Theoretical prediction of new noble-gas molecules FNgBNR (Ng = Ar, Kr, and Xe; R = H, CH3, CCH, CHCH2, F, and OH)

We have computationally predicted a new class of stable noble-gas molecules FNgBNR (Ng = Ar, Kr, Xe; R = H, CH3, CCH, CHCH2, F, and OH). The FNgBNR were found to have compact structures with F-Ng bond lengths of 1.9-2.2 Å and Ng-B bond lengths of ~1.8 Å. The endoergic three-body dissociation energies of FNgBNH to F + Ng + BNH were calculated to be 12.8, 31.7, and 63.9 kcal mol(-1), for Ng = Ar, Kr, and Xe, respectively at the CCSD(T)/CBS level. The energy barriers of the exoergic two-body dissociation to Ng + FBNH were calculated to be 16.1, 24.0, and 33.2 kcal mol(-1) for Ng = Ar, Kr, and Xe, respectively. Our results showed that the dissociation energetics is relatively insensitive to the identities of the terminal R groups. The current study suggested that a wide variety of noble-gas containing molecules with different types of R groups can be thermally stable at low temperature, and the number of potentially stable noble-gas containing molecules would thus increase very significantly. It is expected some of the FNgBNR molecules could be identified in future experiments under cryogenic conditions in noble-gas matrices or in the gas phase.

Ab initio study of the organic xenon insertion compound into ethylene and ethane

This paper studies Xe-insertion ethylene and ethane compounds, i.e., HXeC2H3 and HXeC2H5. The structures, harmonic frequencies, and energetics for both molecules have been calculated at the MP2(full)/6-311++G(2d,2p) level. Our theoretical results predict the existence of HXeC2H3 and the instability of HXeC2H5. Natural bond orbital (NBO) analysis shows a strong ionic bond between the xenon atom and hydrocarbon radical. In addition, the interaction between the donor (Xe lone pair) and acceptor (the C-C antibonding orbital, i.e., π*(C-C)) increases the stability of HXeC2H3.

Theoretical prediction on the structures and stability of the noble-gas containing anions FNgCC- (Ng=He, Ar, Kr, and Xe)

We have made high-level theoretical study on a new type of noble-gas (Ng) containing anions FNgCC(-). The calculated short Ng-CC bond lengths of 1.13, 1.77, 1.89, and 2.04 Å for Ng=He, Ar, Kr, and Xe, respectively, and the electron density distributions indicated strong covalent interactions between the Ng and CC induced by the polarizing fluoride ion. Except for FHeCC(-), the structures of all other FNgCC(-) were predicted to be linear. The intrinsic stability of the FNgCC(-) was studied by calculating the energies of the three-body dissociation reaction: FNgCC(-) → F(-) + Ng + CC and by calculating the energy barriers of the two-body dissociation reaction: FNgCC(-) → Ng + FCC(-). The results showed that FNgCC(-) (Ng=Ar, Kr, Xe) could be kinetically stable in the gas phase with the three-body dissociation energies of 17, 37, and 64 kcal/mol and two body-dissociation barriers of 22, 31, and 42 kcal/mol, respectively, at the coupled-cluster single double (triple)/aug-cc-pVQZ level of theory. The structures and the stability were also confirmed using the multi-reference CASPT2 calculation. Future experimental identification of the FNgCC(-) anions is expected under cryogenic conditions.

Infrared spectra of NgBeS (Ng = Ne, Ar, Kr, Xe) and BeS2 in noble-gas matrices

Laser-ablated beryllium atom has been codeposited at 4 K with hydrogen sulfide in excess noble gas matrices. Four noble-gas compounds NgBeS (Ng = Ne, Ar, Kr, Xe) and the BeS(2) molecule are identified on the basis of the S-34 isotopic substitution, DFT and CCSD(T) theoretical predictions, and a comparison of noble-gas substitution. The agreement between the experimental and calculated vibrational frequencies supports the identification of these molecules. The dissociation energies are calculated at 1.6, 12.6, 10.7, and 13.4 kcal/mol for NeBeS, ArBeS, KrBeS, and XeBeS, respectively, at the CCSD(T) level. The BeS Lewis acid molecule favors strong chemical binding between the Be and Ng atoms.

Synthesis of a uranium(VI)-carbene: reductive formation of uranyl(V)-methanides, oxidative preparation of a [R2C═U═O]2+ analogue of the [O═U═O]2+ uranyl ion (R = Ph2PNSiMe3), and comparison of the nature of U(IV)═C, U(V)═C, and U(VI)═C double bonds

We report attempts to prepare uranyl(VI)- and uranium(VI) carbenes utilizing deprotonation and oxidation strategies. Treatment of the uranyl(VI)-methanide complex [(BIPMH)UO(2)Cl(THF)] [1, BIPMH = HC(PPh(2)NSiMe(3))(2)] with benzyl-sodium did not afford a uranyl(VI)-carbene via deprotonation. Instead, one-electron reduction and isolation of di- and trinuclear [UO(2)(BIPMH)(μ-Cl)UO(μ-O){BIPMH}] (2) and [UO(μ-O)(BIPMH)(μ(3)-Cl){UO(μ-O)(BIPMH)}(2)] (3), respectively, with concomitant elimination of dibenzyl, was observed. Complexes 2 and 3 represent the first examples of organometallic uranyl(V), and 3 is notable for exhibiting rare cation-cation interactions between uranyl(VI) and uranyl(V) groups. In contrast, two-electron oxidation of the uranium(IV)-carbene [(BIPM)UCl(3)Li(THF)(2)] (4) by 4-morpholine N-oxide afforded the first uranium(VI)-carbene [(BIPM)UOCl(2)] (6). Complex 6 exhibits a trans-CUO linkage that represents a [R(2)C═U═O](2+) analogue of the uranyl ion. Notably, treatment of 4 with other oxidants such as Me(3)NO, C(5)H(5)NO, and TEMPO afforded 1 as the only isolable product. Computational studies of 4, the uranium(V)-carbene [(BIPM)UCl(2)I] (5), and 6 reveal polarized covalent U═C double bonds in each case whose nature is significantly affected by the oxidation state of uranium. Natural Bond Order analyses indicate that upon oxidation from uranium(IV) to (V) to (VI) the uranium contribution to the U═C σ-bond can increase from ca. 18 to 32% and within this component the orbital composition is dominated by 5f character. For the corresponding U═C π-components, the uranium contribution increases from ca. 18 to 26% but then decreases to ca. 24% and is again dominated by 5f contributions. The calculations suggest that as a function of increasing oxidation state of uranium the radial contraction of the valence 5f and 6d orbitals of uranium may outweigh the increased polarizing power of uranium in 6 compared to 5.

Benchmark of density functional theory methods on the prediction of bond energies and bond distances of noble-gas containing molecules

We have tested three pure density functional theory (DFT) functionals, BLYP, MPWPW91, MPWB95, and ten hybrid DFT functionals, B3LYP, B3P86, B98, MPW1B95, MPW1PW91, BMK, M05-2X, M06-2X, B2GP-PLYP, and DSD-BLYP with a series of commonly used basis sets on the performance of predicting the bond energies and bond distances of 31 small neutral noble-gas containing molecules. The reference structures were obtained using the CCSD(T)∕aug-cc-pVTZ theory and the reference energies were based on the calculation at the CCSD(T)∕CBS level. While in general the hybrid functionals performed significantly better than the pure functionals, our tests showed a range of performance by these hybrid functionals. For the bond energies, the MPW1B95∕6-311+G(2df,2pd), BMK∕aug-cc-pVTZ, B2GP-PLYP∕aug-cc-pVTZ, and DSD-BLYP∕aug-cc-pVTZ methods stood out with mean unsigned errors of 2.0-2.3 kcal∕mol per molecule. For the bond distances, the MPW1B95∕6-311+G(2df,2pd), MPW1PW91∕6-311+G(2df,2pd), and B3P86∕6-311+G(2df,2pd), DSD-BLYP∕6-311+G(2df,2pd), and DSD-BLYP∕aug-cc-pVTZ methods stood out with mean unsigned errors of 0.008-0.013 Å per bond. The current study showed that a careful selection of DFT functionals is very important in the study of noble-gas chemistry, and the most recommended methods are MPW1B95∕6-311+G(2df,2pd) and DSD-BLYP∕aug-cc-pVTZ.

Review: gas-phase ion chemistry of the noble gases: recent advances and future perspectives

This review article surveys recent experimental and theoretical advances in the gas-phase ion chemistry of the noble gases. Covered issues include the interaction of the noble gases with metal and non-metal cations, the conceivable existence of covalent noble-gas anions, the occurrence of ion-molecule reactions involving singly-charged xenon cations, and the occurrence of bond-forming reactions involving doubly-charged cations. Research themes are also highlighted, that are expected to attract further interest in the future.

Theoretical prediction of stable noble-gas anions XeNO(2)(-) and XeNO(3)(-) with very short xenon-nitrogen bond lengths

We have predicted a new type of noble-gas anions, XeNO(2)(-) and XeNO(3)(-) with very short Xe-N bond lengths ( approximately 1.8 A), using high-level electronic structure theory with extended atomic basis sets. The chemical bonding between xenon and nitrogen atoms could formally be assigned as triple bonds. The best estimates of the atomization energies of the two anions were found to be 50 and 101 kcal/mol, respectively, and the lowest unimolecular dissociation barriers were estimated to be approximately 42 kcal/mol. These anions were predicted to be kinetically stable at low temperature. The possible neutral "salts" formed between the lithium cation and these two anions were also discussed.

Stabilization of HHeF by complexation: is it a really viable strategy?

Ab initio calculations at the MP2 and CCSD(T) levels of theory have disclosed the conceivable existence of fluorine-coordinated complexes of HHeF with alkali-metal ions and molecules M(+) (M(+)=Li(+)-Cs(+)), M(+)-OH(2), M(+)-NH(3) (M(+)=Li(+), Na(+)), and MX (M=Li, Na; X=F, Cl, Br). All these ligands L induce a shortening of the H-He distance and a lengthening of the He-F distance accompanied by consistent blue- and redshifts, respectively, of the H-He and He-F stretching modes. These structural effects are qualitatively similar to those predicted for other investigated complexes of the noble gas hydrides HNgY, but are quantitatively more pronounced. For example, the blueshifts of the H-He stretching mode are exceptionally large, ranging between around 750 and 1000 cm(-1). The interactions of HHeF with the ligands investigated herein also enhance the (HHe)(+)F(-) dipole character and produce large complexation energies of around 20-60 kcal mol(-1). Most of the HHeF-L complexes are indeed so stable that the three-body dissociation of HHeF into H+He+F, exothermic by around 25-30 kcal mol(-1), becomes endothermic. This effect is, however, accompanied by a strong decrease in the H-He-F bending barrier. The complexation energies, DeltaE, and the bending barriers, E*, are, in particular, related by the inverse relationship E*(kcal mol(-1))=6.9exp[-0.041DeltaE(kcal mol(-1))]. Therefore the HHeF-L complexes, which are definitely stable with respect to H+He+F+L (DeltaE approximately 25-30 kcal mol(-1)), are predicted to have bending barriers of only 0.5-2 kcal mol(-1). Overall, our calculations cast doubt on the conceivable stabilization of HHeF by complexation.

Formation and characterization of magnesium bisozonide and carbonyl complexes in solid argon

The reactions of magnesium atoms with dioxygen and dioxygen/carbon monoxide mixture have been investigated by matrix isolation infrared absorption spectroscopy. Magnesium atoms react with dioxygen in solid argon to form the inserted MgO(2) molecules under UV excitation, which were previously characterized. Annealing allows the dioxygen molecules to diffuse and to react with MgO(2) and form the magnesium bisozonide complex, Mg(O(3))(2), which is proposed to be coordinated by two argon atoms in solid argon matrix. The Mg(O(3))(2)(Ar)(2) complex is characterized to have two equivalent side-on bonded ozonide ligands with a D(2h) symmetry. The coordinated argon atoms can be replaced by carbon monoxide to give the magnesium bisozonide dicarbonyl complex, Mg(O(3))(2)(CO)(2), a neutral magnesium carbonyl complex with CO binding to the Mg(2+) center.

Cationic noble gas hydrides: a theoretical investigation of dinuclear HNgFNgH+ (Ng = He-Xe)

Theoretical calculations at the B3LYP, MP2, and CCSD(T) levels of theory disclose the conceivable existence of cationic noble gas hydrides containing two Ng atoms. These species have a general formula of HNgFNgH(+) (Ng = He-Xe), and are the cationic counterparts of the neutral HNgF. The optimized geometries, harmonic frequencies, and bonding properties point to ion-dipole complexes between a fluoride anion and two covalent H-Ng(+) cations, best formulated as (H-Ng(+))(2)F(-). The HXeFXeH(+) is also isoelectronic with the recently experimentally observed HXeOXeH (Khriachtchev et al. J. Am. Chem. Soc. 2008, 130, 6114-6118). The resulting HNgFNgH(+) are thermochemically stable with respect to dissociation into HNg(+) + HNgF and HNg(+) + H + Ng + F, but are largely unstable with respect to both the loss of HF (with formation of HNg(+) + Ng) and H(2)F(+) (with formation of two Ng atoms). These decompositions pass through bent transition structures, and only the heaviest HArFArH(+), HKrFKrH(+), and HXeFXeH(+) are protected by energy barriers large enough (ca. 10-15 kcal mol(-1)) to support their conceivable metastability. In line with other series of noble gas compounds, the neon cation HNeFNeH(+) is the least stable among the various HNgFNgH(+).

A DFT study of the reactivity of actinidocenes (U, Np and Pu) with pyridine and pyridine N-oxide derivatives

The ortho C-H bond activation of several pyridine and pyridine N-oxide derivatives mediated by Cp(2)An(IV)(CH(3))(2) and Cp(2)An(III)(CH(3)) (Cp = C(5)H(5) and An = U, Np, Pu) have been investigated at the DFT level. For uranium(IV) complex, an excellent agreement with experimental observations is found, and particularly in the case of 2-picoline where only ortho sp(2) C-H activation is observed without any sp(3) C-H activation. These differences of reactivity can be explained by the charges distribution at the metathesis transition state level. A predictive study of the reactivity of neptunium and plutonium complexes with pyridine and pyridine N-oxide is reported. This study shows that neptunium and plutonium have almost the same reactivity. The C-H activation mediated by actinide (III) complexes have found to be more kinetically and thermodynamically favorable than for actinide (IV) complexes. The influence of 5f electrons on organoactinide reactivity is found to be small by comparing implicit and explicit treatment of 5f electrons.

Reactions of molybdenum and tungsten atoms with nitrous oxide in excess argon: a combined matrix infrared spectroscopic and theoretical study

Reactions of laser-ablated Mo and W atoms with the N(2)O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. In the reaction of the N(2)O molecule with the Mo atom, the absorptions at 1960.3 and 934.4 cm(-1) are assigned to the N-N and Mo-O stretching vibrations of the OMoNN complex, respectively. An analogous OWNN complex has also been observed in the W + N(2)O reaction. Infrared spectroscopy also provides evidence for the formation of the OW(NN)(2) complexes. Density functional theory calculations have been performed on the products. Overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Furthermore, a plausible reaction mechanism for the formation of these products has been proposed.