Chromium(VI) Oxyfluoride Dianions, [Cr2 O4 F6 ]2- and [CrO2 F4 ]2- ; Syntheses and Structures of [XeF5 ]2 [Cr2 O4 F6 ], [XeF5 ]2 [Cr2 O4 F6 ] ⋠nX (X=HF, n=4; X=XeOF4 , n=2), and [XeF5 ][Xe2 F11 ][CrO2 F4 ].

The fluorobasic character of the strong oxidative fluorinator, XeF6 , and the oxidative resistance of the [XeF5 ]+ and [Xe2 F11 ]+ cations have been exploited for the syntheses of several novel Cr(VI) dianion salts. The reactions of XeF6 and CrO2 F2 in anhydrous HF and by direct fusion of the reactants in melts have yielded the first dinuclear Cr(VI) oxyfluoro-dianion salts, [XeF5 ]2 [Cr2 O4 F6 ], [XeF5 ]2 [Cr2 O4 F6 ] ⋅ 4HF, [XeF5 ]2 [Cr2 O4 F6 ] ⋅ 2XeOF4 , and mononuclear Cr(VI) oxyfluoro-dianion salt, [XeF5 ][Xe2 F11 ][CrO2 F4 ]. The salts were structurally characterized by low-temperature (LT) single-crystal X-ray diffraction (SCXRD) and LT Raman spectroscopy. The [CrO2 F4 ]2- and [Cr2 O4 F6 ]2- dianions have distorted octahedral cis-dioxo Cr(VI) coordination spheres in which two F-atoms are trans to one another and two F-atoms are trans to O-atoms, where the [Cr2 O4 F6 ]2- dianion is the fluorine-bridged dimer of the [CrO2 F3 ]- anion. Quantum-chemical calculations were used to obtain the energy-minimized, gas-phase geometries, and the calculated vibrational spectra of the gas-phase dianions and their ion-pairs, which were used to aid in the vibrational frequency assignments of the crystalline salts. NBO and MEPS analyses and SCXRD show these salts are comprised of intimate ion-pairs in which their cations and anions interact through primarily electrostatic Xe- - -F σ-hole bonds.

XeF2 Coordination Complexes of the [BrO2]+ Cation, [O2Br(FXeF)n][AsF6] (n = 1, 2) and [O2Br(FXeF)2][SbF6]; Their Syntheses and Structural Characterizations.

The syntheses and structural characterizations of the first XeF2 coordination complexes of the [BrO2]+ cation are described. The reactions of [BrO2][PnF6] (Pn = As, Sb) with XeF2 in anhydrous HF solvent yield the salts [O2Br(FXeF)n][AsF6] (n = 1, 2) and [O2Br(FXeF)2][SbF6], which were characterized by low-temperature (LT) Raman spectroscopy and single-crystal X-ray diffraction (SCXRD). The XeF2 ligands and [PnF6]- coordinate to the Lewis acidic [BrO2]+ cation through primarily electrostatic BrV---FXe σ-hole bonds that result from coordination of the F atoms into regions of high positive electrostatic potential on the Br(V) atom and have bond trajectories that avoid the stereoactive valence electron lone-pair of Br(V). The complexes and their structural characterizations by LT Raman spectroscopy and SCXRD significantly extend the coordination chemistry of Br(V) and provide rare examples of a noble-gas difluoride coordinated to a strong oxidant main-group Lewis acid center.

Synthesis, Structure, and Bonding of a XeIV Transition-Metal Coordination Complex, F3 XeFb - - -WOF4.

The coordination complex, F3 XeFb - - -WOF4 , was synthesized in CFCl3 solvent by reaction of the weak fluoride-ion donor and strong oxidative fluorinating agent, XeF4 , with the moderate-strength fluoride-ion acceptor, WOF4 . The compound is the only transition-metal coordination complex of XeIV and was characterized at low temperatures by single-crystal X-ray diffraction and Raman spectroscopy. Xenon tetrafluoride and WOF4 coordinate trans to the W=O bond through a W- - -Fb bond. The XeF3 moiety of F3 XeFb - - -WOF4 acquires a degree of [XeF3 ]+ character upon coordination that is reflected by its Xe-F stretching frequencies which are intermediate with respect to those of XeF4 and [XeF3 ]+ . Calculations show W- - -Fb is predominantly an electrostatic, σ-hole bond with a significant orbital contribution that accounts for the bent Xe-Fb - - -W angle. The calculations show F3 XeFb - - -MOF4 (M=Cr, Mo) are less stable than their W analogue, consistent with failed attempts to synthesize F3 XeFb - - -MoOF4 .

Noble-Gas Difluoride Complexes of MOF4 (M=Mo, W); Syntheses, Structures and Bonding of NgF2 ⋠MOF4 and XeF2 ⋠2MOF4 (Ng=Kr, Xe).

The NgF2 ⋅ MOF4 (Ng=Kr, Xe; M=Mo, W) and XeF2 ⋅ 2MOF4 complexes were synthesized in anhydrous HF (aHF) solvent and melts, respectively. Their single-crystal X-ray diffraction (SCXRD) structures show NgF2 ⋅ MOF4 and XeF2 ⋅ 2MOF4 have Ft -Ng-Fb - - -M arrangements, in which the NgF2 ligands coordinate to MOF4 through Ng-Fb - - -M bridges. The XeF2 ligands of XeF2 ⋅ 2MOF4 also coordinate to F3 OM-Fb '- - -M'OF4 moieties through Xe-Fb - - -M bridges to form Ft -Xe-Fb - - -M(OF3 )-Fb '- - -M'OF4 , where XeF2 coordinates trans to the M=O bond and Fb ' coordinates trans to the M'=O bond. The Ng-Ft , Ng-Fb , and M- - -Fb bond lengths of NgF2 ⋅ nMOF4 are consistent with MOF4 and F3 OM-Fb '- - -M'OF4 fluoride-ion affinity trends: CrOF4

Syntheses and Characterizations of the Mixed Noble-Gas Compounds, [FKrII FXeII F][AsF6 ]⋠0.5 KrII F2 ⋠2 HF, ([KrII 2 F3 ][AsF6 ])2 ⋠XeIV F4 , and XeIV F4 ⋠KrII F2.

Reaction of [XeF][AsF6 ] with excess KrF2 at -78 °C in anhydrous HF (aHF) solvent has yielded the first mixed KrII /XeII noble-gas compound, [FKrFXeF][AsF6 ] ⋅0.5 KrF2 ⋅2 HF, a salt of the [FKrFXeF]+ cation. The potent oxidative fluorinating properties of KrII fluoride species resulted in oxidation of XeII to XeIV in aHF at -60 °C to form the mixed KrII /XeIV cocrystals, ([Kr2 F3 ][AsF6 ])2 ⋅XeF4 and XeF4 ⋅KrF2 . Further decomposition at 22 °C resulted in oxidation of XeIV to XeVI to give the recently reported KrII /XeVI complexes, [F5 Xe(FKrF)n ][AsF6 ] (n=1, 2), [F5 Xe][AsF6 ], and a new KrII /XeVI complex, [(F5 Xe)2 (µ-FKrF)(AsF6 )2 ], which was characterized by low-temperature (LT) Raman spectroscopy. The [FKrFXeF][AsF6 ]⋅0.5 KrF2 ⋅2 HF, ([Kr2 F3 ][AsF6 ])2 ⋅XeF4 , and XeF4 ⋅KrF2 compounds were characterized by LT Raman spectroscopy and single-crystal X-ray diffraction. Quantum-chemical calculations were used to assess the bonding in [FKrFXeF]+ , [Kr2 F3 ]+ , and [Xe2 F3 ]+ and to aid in their vibrational assignments.

Mixed Noble-Gas Compounds of Krypton(II) and Xenon(VI); [F5 Xe(FKrF)AsF6 ] and [F5 Xe(FKrF)2 AsF6 ].

The coordination chemistry of KrF2 has been limited in contrast with that of XeF2 , which exhibits a far richer coordination chemistry with main-group and transition-metal cations. In the present work, reactions of [XeF5 ][AsF6 ] with KrF2 in anhydrous HF solvent afforded [F5 Xe(FKrF)AsF6 ] and [F5 Xe(FKrF)2 AsF6 ], the first mixed krypton/xenon compounds. X-ray crystal structures and Raman spectra show the KrF2 ligands and [AsF6 ]- anions are F-coordinated to the xenon atoms of the [XeF5 ]+ cations. Quantum-chemical calculations are consistent with essentially noncovalent ligand-xenon bonds that may be described in terms of σ-hole bonding. These complexes significantly extend the XeF2 -KrF2 analogy and the limited chemistry of krypton by introducing a new class of coordination compound in which KrF2 functions as a ligand that coordinates to xenon(VI). The HF solvates, [F5 Xe(FH)AsF6 ] and [F5 Xe(FH)SbF6 ], are also characterized in this study and they provide rare examples of HF coordinated to xenon(VI).

Group†6 Oxyfluoro-Anion Salts of [XeF5 ]+ and [Xe2 F11 ]+ : Syntheses and Structures of [XeF5 ][M2 O2 F9 ] (M=Mo, W), [Xe2 F11 ][M'OF5 ] (M'=Cr, Mo, W), [XeF5 ][HF2 ]⋠CrOF4 , and [XeF5 ][WOF5 ]⋠XeOF4.

The reactions of the fluoride-ion donor, XeF6 , with the fluoride-ion acceptors, M'OF4 (M'=Cr, Mo, W), yield [XeF5 ]+ and [Xe2 F11 ]+ salts of [M'OF5 ]- and [M2 O2 F9 ]- (M=Mo, W). Xenon hexafluoride and MOF4 react in anhydrous hydrogen fluoride (aHF) to give equilibrium mixtures of [Xe2 F11 ]+ , [XeF5 ]+ , [(HF)n F]- , [MOF5 ]- , and [M2 O2 F9 ]- from which the title salts were crystallized. The [XeF5 ][CrOF5 ] and [Xe2 F11 ][CrOF5 ] salts could not be formed from mixtures of CrOF4 and XeF6 in aHF at low temperature (LT) owing to the low fluoride-ion affinity of CrOF4 , but yielded [XeF5 ][HF2 ]⋅CrOF4 instead. In contrast, MoOF4 and WOF4 are sufficiently Lewis acidic to abstract F- ion from [(HF)n F]- in aHF to give the [MOF5 ]- and [M2 O2 F9 ]- salts of [XeF5 ]+ and [Xe2 F11 ]+ . To circumvent [(HF)n F]- formation, [Xe2 F11 ][CrOF5 ] was synthesized at LT in CF2 ClCF2 Cl solvent. The salts were characterized by LT Raman spectroscopy and LT single-crystal X-ray diffraction, which provided the first X-ray crystal structure of the [CrOF5 ]- anion and high-precision geometric parameters for [MOF5 ]- and [M2 O2 F9 ]- . Hydrolysis of [Xe2 F11 ][WOF5 ] by water contaminant in HF solvent yielded [XeF5 ][WOF5 ]⋅XeOF4 . Quantum-chemical calculations were carried out for M'OF4 , [M'OF5 ]- , [M'2 O2 F9 ]- , {[Xe2 F11 ][CrOF5 ]}2 , [Xe2 F11 ][MOF5 ], and {[XeF5 ][M2 O2 F9 ]}2 to obtain their gas-phase geometries and vibrational frequencies to aid in their vibrational mode assignments and to assess chemical bonding.

Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5 ]+ and [Xe2 F11 ]+ Salts of the [CrVI OF5 ]- , [CrV OF5 ]2- , [CrV 2 O2 F8 ]2- , and [CrIV F6 ]2- Anions.

Molten mixtures of XeF6 and CrVI OF4 react by means of F2 elimination to form [XeF5 ][Xe2 F11 ][CrV OF5 ]⋅2 CrVI OF4 , [XeF5 ]2 [CrIV F6 ]⋅2 CrVI OF4 , [Xe2 F11 ]2 [CrIV F6 ], and [XeF5 ]2 [CrV 2 O2 F8 ], whereas their reactions in anhydrous hydrogen fluoride (aHF) and CFCl3 /aHF yield [XeF5 ]2 [CrV 2 O2 F8 ]⋅2 HF and [XeF5 ]2 [CrV 2 O2 F8 ]⋅2 XeOF4 . Other than [Xe2 F11 ][MVI OF5 ] and [XeF5 ][MVI 2 O2 F9 ] (M=Mo or W), these salts are the only Group 6 oxyfluoro-anions known to stabilize noble-gas cations. Their reaction pathways involve redox transformations that give [XeF5 ]+ and/or [Xe2 F11 ]+ salts of the known [CrV OF5 ]2- and [CrIV F6 ]2- anions, and the novel [CrV 2 O2 F8 ]2- anion. A low-temperature Raman spectroscopic study of an equimolar mixture of solid XeF6 and CrOF4 revealed that [Xe2 F11 ][CrVI OF5 ] is formed as a reaction intermediate. The salts were structurally characterized by LT single-crystal X-ray diffraction and LT Raman spectroscopy, and provide the first structural characterizations of the [CrV OF5 ]2- and [CrV 2 O2 F8 ]2- anions, where [CrV 2 O2 F8 ]2- represents a new structural motif among the known oxyfluoro-anions of Group 6. The X-ray structures show that [XeF5 ]+ and [Xe2 F11 ]+ form ion pairs with their respective anions by means of Xe- - -F-Cr bridges. Quantum-chemical calculations were carried out to obtain the energy-minimized, gas-phase geometries and the vibrational frequencies of the anions and their ion pairs and to aid in the assignments of their Raman spectra.

Xenon Trioxide Adducts of O-Donor Ligands; [(CH3 )2 CO]3 XeO3 , [(CH3 )2 SO]3 (XeO3 )2 , (C5 H5 NO)3 (XeO3 )2 , and [(C6 H5 )3 PO]2 XeO3.

Xenon trioxide (XeO3 ) forms adducts with triphenylphosphine oxide, dimethylsulfoxide, pyridine-N-oxide, and acetone by coordination of the ligand oxygen atoms to the XeVI atom of XeO3 . The crystalline adducts were characterized by low-temperature, single-crystal X-ray diffraction, and Raman spectroscopy. Unlike solid XeO3 , which detonates when mechanically or thermally shocked, solid (C5 H5 NO)3 (XeO3 )2 , [(C6 H5 )3 PO]2 XeO3 , and [(CH3 )2 SO]3 (XeO3 )2 are insensitive to mechanical shock. The [(CH3 )2 SO]3 (XeO3 )2 adduct slowly decomposes over several days to (CH3 )2 SO2 , Xe, and O2 . All three complexes undergo rapid deflagration when ignited by a flame. Both [(C6 H5 )3 PO]2 XeO3 and (C5 H5 NO)3 (XeO3 )2 are room-temperature stable and the [(CH3 )2 CO]3 XeO3 complex dissociates at room temperature to form a stable solution of XeO3 in acetone. The xenon coordination sphere of [(C6 H5 )3 PO]2 XeO3 , a distorted square-pyramid, provides the first example of a five-coordinate XeO3 complex with only two Xe- - -O adduct bonds. The xenon coordination spheres of the remaining adducts are distorted octahedra, comprised of three Xe- - -O secondary bonds that are approximately trans to the primary Xe-O bonds of XeO3 . Quantum-chemical calculations were used to assess the nature of the Xe- - -O adduct bonds, which are described as predominantly electrostatic bonds between the nucleophilic oxygen atoms of the bases and the σ-holes of the electrophilic xenon atoms.

Syntheses, Structures, and Bonding of NgF2 ⋠CrOF4 , NgF2 ⋠2CrOF4 (Ng=Kr, Xe), and (CrOF4 )∞.

The noble-gas difluoride adducts, NgF2 ⋅CrOF4 and NgF2 ⋅2CrOF4 (Ng=Kr and Xe), have been synthesized and structurally characterized at low temperatures by Raman spectroscopy and single-crystal X-ray diffraction. The low fluoride ion affinity of CrOF4 renders it incapable of inducing fluoride ion transfer from NgF2 (Ng=Kr and Xe) to form ion-paired salts of the [NgF]+ cations having either the [CrOF5 ]- or [Cr2 O2 F9 ]- anions. The crystal structures show the NgF2 ⋅CrOF4 adducts are comprised of Ft -Ng-Fb - - -Cr(O)F4 structural units in which NgF2 is weakly coordinated to CrOF4 by means of a fluorine bridge, Fb , in which Ng-Fb is elongated relative to the terminal Ng-Ft bond. In contrast with XeF2 ⋅2MOF4 (M=Mo or W) and KrF2 ⋅2MoOF4 , in which the Lewis acidic, F4 (O)M- - -Fb - - -M(O)F3 moiety coordinates to Ng through a single M- - -Fb -Ng bridge, both fluorine ligands of NgF2 coordinate to CrOF4 molecules to form F4 (O)Cr- - -Fb -Ng-Fb - - -Cr(O)F4 adducts in which both Ng-Fb bonds are only marginally elongated relative to the Ng-F bonds of free NgF2 . Quantum-chemical calculations show that the Cr-Fb bonds of NgF2 ⋅CrOF4 and NgF2 ⋅2CrOF4 are predominantly electrostatic with a small degree of covalent character that accounts for their nonlinear Cr- - -Fb -Ng bridge angles and staggered O-Cr- - -Fb -Ng-Ft dihedral angles. The crystal structures and Raman spectra of two CrOF4 polymorphs have also been obtained. Both are comprised of fluorine-bridged chains that are cis- and trans-fluorine-bridged with respect to oxygen.

A Stable Crown Ether Complex with a Noble-Gas Compound.

Crown ethers have been known for over 50 years, but no example of a complex between a noble-gas compound and a crown ether or another polydentate ligand had previously been reported. Xenon trioxide is shown to react with 15-crown-5 to form the kinetically stable (CH2 CH2 O)5 XeO3 adduct, which, in marked contrast with solid XeO3 , does not detonate when mechanically shocked. The crystal structure shows that the five oxygen atoms of the crown ether are coordinated to the xenon atom of XeO3 . The gas-phase Wiberg bond valences and indices and the empirical bond valences indicate that the Xe- - -Ocrown bonds are predominantly electrostatic and are consistent with σ-hole bonding. Mappings of the electrostatic potential (EP) onto the Hirshfeld surfaces of XeO3 and 15-crown-5 in (CH2 CH2 O)5 XeO3 and a detailed examination of the molecular electrostatic potential surface (MEPS) of XeO3 and (CH2 CH2 O)5 reveal regions of negative EP on the oxygen atoms of (CH2 CH2 O)5 and regions of high positive EP on the xenon atom, which are also in accordance with σ-hole interactions.

Coordination of KrF2 to a Naked Metal Cation, Mg2.

Examples of coordination compounds in which KrF2 functions as a ligand are very rare. In contrast, XeF2 provides a rich coordination chemistry with a variety of main-group and transition metal cations. The reactions of Mg(AsF6 )2 and KrF2 in HF or BrF5 solvent have afforded [Mg(KrF2 )4 (AsF6 )2 ] and [Mg(KrF2 )4 (AsF6 )2 ]⋅2 BrF5 , respectively, the first examples of a metal cation ligated by KrF2 . Their X-ray crystal structures and Raman spectra show that the KrF2 ligands and [AsF6 ]- anions are F-coordinated to a naked Mg2+ cation. Quantum-chemical calculations are consistent with essentially non-covalent ligand-metal bonding. These compounds significantly extend the XeF2 -KrF2 analogy and the limited chemistry of krypton by introducing a new class of coordination compound in which KrF2 functions as a ligand towards a naked metal cation.

Syntheses and Structures of Xenon Trioxide Alkylnitrile Adducts.

The potent oxidizer and highly shock-sensitive binary noble-gas oxide XeO3 interacts with CH3 CN and CH3 CH2 CN to form O3 XeNCCH3 , O3 Xe(NCCH3 )2 , O3 XeNCCH2 CH3 , and O3 Xe(NCCH2 CH3 )2 . Their low-temperature single-crystal X-ray structures show that the xenon atoms are consistently coordinated to three donor atoms, which results in pseudo-octahedral environments around the xenon atoms. The adduct series provides the first examples of a neutral xenon oxide bound to nitrogen bases. Raman frequency shifts and Xe-N bond lengths are consistent with complex formation. Energy-minimized gas-phase geometries and vibrational frequencies were obtained for the model compounds O3 Xe(NCCH3 )n (n=1-3) and O3 Xe(NCCH3 )n ⋅[O3 Xe(NCCH3 )2 ]2 (n=1, 2). Natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses were carried out to further probe the nature of the bonding in these adducts.

Nature of the Xe(VI)-N Bonds in F6 XeNCCH3 and F6 Xe(NCCH3)2 and the Stereochemical Activity of Their Xenon Valence Electron Lone Pairs.

The recently reported syntheses and X-ray crystal structures of the highly endothermic compounds F6XeNCCH3 and F6Xe(NCCH3)2 ⋅CH3CN provide the first, albeit weakly covalent, Xe(VI)-N bonds. The XeF6 unit of F6 XeNCCH3 possesses distorted octahedral (C3v ) symmetry similar to gas-phase XeF6 , whereas the XeF6 unit of F6 Xe(NCCH3)2 ⋅CH3CN possesses C2v symmetry. Herein, the natural bond orbital (NBO), atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses show that the Xe valence electron lone pairs (VELPs) of both compounds are stereochemically active. The Xe VELPS are diffuse and ineffectively screen their Xe cores so that the Xe VELP positions correspond to the most electrophilic regions of the MEPS, which enables the opposing N VELP of CH3CN to coordinate to this region. These bonds are predominantly electrostatic in nature and are interpreted as σ-hole interactions.

Thiazyl Trifluoride (NSF3) Adducts and Imidodifluorosulfate (F2OSN-) Derivatives of Hg(OTeF5)2.

Reactions of Hg(OTeF5)2 with excess amounts of NSF3 at 0 °C result in the formation of NSF3 adducts having the compositions [Hg(OTeF5)2·N≡SF3]∞ (1), [Hg(OTeF5)2·2N≡SF3]2 (2), and Hg3(OTeF5)6·4N≡SF3 (3). When the reactions are carried out at room temperature, oxygen/fluorine metatheses occur yielding the F2OSN- derivatives [Hg(OTeF5)(N═SOF2)·N≡SF3]∞ (4) and [Hg3(OTeF5)5(N═SOF2)·2N≡SF3]2 (5). The proposed reaction pathway leading to F2OSN- group formation occurs by nucleophilic attack by a F5TeO- group at the sulfur(VI) atom of NSF3, followed by TeF6 elimination. Tellurium hexafluoride formation was confirmed by (19)F NMR spectroscopy. The NSF3 molecules are terminally N-coordinated to mercury, whereas the F2OSN- ligands are N-bridged to two mercury atoms. The compound series was characterized by low-temperature single-crystal X-ray diffraction and low-temperature Raman spectroscopy. Several structural motifs are observed within this structurally diverse series. These include the infinite chain structures of the related compounds, 1 and 4; 2, a dimeric structure which possesses an (HgO(µ))2 ring at its core; 3, a structure based on a cage comprised of a (HgO(µ))3 ring that is capped on each face by µ(3)-oxygen bridged F5TeO- groups; and 5, a dimeric structure possessing two distorted (Hg3O2N) rings that are formally derived from 3 by replacement of a F5TeO- group by a F2OSN- group in each ring. Quantum-chemical calculations were carried out to gain insight into the bonding of the µ(3)-oxygen bridged teflate groups observed in structure 3. Compounds 1-5 represent a novel class of neutral transition metal complexes with NSF3, providing the first examples of NSF3 coordination to mercury. Compounds 4 and 5 also provide the only examples of F2OSN- derivatives of mercury that have been characterized by single-crystal X-ray diffraction.

[XeOXeOXe](2+), the Missing Oxide of Xenon(II); Synthesis, Raman Spectrum, and X-ray Crystal Structure of [XeOXeOXe][µ-F(ReO2F3)2]2.

The [XeOXeOXe](2+) cation provides an unprecedented example of a xenon(II) oxide and a noble-gas oxocation as well as a rare example of a noble-gas dication. The [XeOXeOXe](2+) cation was synthesized as its [µ-F(ReO2F3)2](-) salt by reaction of ReO3F with XeF2 in anhydrous HF at -30 °C. Red-orange [XeOXeOXe][µ-F(ReO2F3)2]2 rapidly decomposes to XeF2, ReO2F3, Xe, and O2 when the solid or its HF solutions are warmed above -20 °C. The crystal structure of [XeOXeOXe][µ-F(ReO2F3)2]2 consists of a planar, zigzag-shaped [XeOXeOXe](2+) cation (C2h symmetry) that is fluorine bridged through its terminal xenon atoms to two [µ-F(ReO2F3)2](-) anions. The Raman spectra of the natural abundance and (18)O-enriched [XeOXeOXe](2+) salts are consistent with a centrosymmetric (C2h) cation geometry. A proposed reaction pathway leading to [XeOXeOXe][µ-F(ReO2F3)2]2 consists of a series of oxygen/fluorine metathesis reactions that are presumably mediated by the transient HOXeF molecule. Quantum-chemical calculations were used to aid in the vibrational assignments of [Xe(16/18)OXe(16/18)OXe][µ-F(Re(16/18)O2F3)2]2 and to assess the bonding in [XeOXeOXe](2+) by NBO, QTAIM, ELF, and MEPS analyses. Ion pair interactions occur through Re-Fµ---Xe bridges, which are predominantly electrostatic in nature and result from polarization of the Fµ-atom electron densities by the exposed core charges of the terminal xenon atoms. Each xenon(II) atom is surrounded by a torus of xenon valence electron density comprised of the three valence electron lone pairs. The positive regions of the terminal xenon atoms and associated fluorine bridge bonds correspond to the positive σ-holes and donor interactions that are associated with "halogen bonding".

Syntheses and Structures of F6 XeNCCH3 and F6 Xe(NCCH3)2.

Acetonitrile and the potent oxidative fluorinating agent XeF6 react at -40 °C in Freon-114 to form the highly energetic, shock-sensitive compounds F6XeNCCH3 (1) and F6Xe(NCCH3)2⋅CH3CN (2⋅CH3CN). Their low-temperature single-crystal X-ray structures show that the adducted XeF6 molecules of these compounds are the most isolated XeF6 moieties thus far encountered in the solid state and also provide the first examples of Xe(VI)-N bonds. The geometry of the XeF6 moiety in 1 is nearly identical to the calculated distorted octahedral (C3v) geometry of gas-phase XeF6. The C2v geometry of the XeF6 moiety in 2 resembles the transition state proposed to account for the fluxionality of gas-phase XeF6. The energy-minimized gas-phase geometries and vibrational frequencies were calculated for 1 and 2, and their respective binding energies with CH3CN were determined. The Raman spectra of 1 and 2⋅CH3CN were assigned by comparison with their calculated vibrational frequencies and intensities.

Lewis acid behavior of SF4 : synthesis, characterization, and computational study of adducts of SF4 with pyridine and pyridine derivatives.

Sulfur tetrafluoride was shown to act as a Lewis acid towards organic nitrogen bases, such as pyridine, 2,6-dimethylpyridine, 4-methylpyridine, and 4-dimethylaminopyridine. The SF4 ⋅NC5 H5 , SF4 ⋅2,6-NC5 H3 (CH3 )2 , SF4 ⋅4-NC5 H4 (CH3 ), and SF4 ⋅4-NC5 H4 N(CH3 )2 adducts can be isolated as solids that are stable below -45 °C. The Lewis acid-base adducts were characterized by low-temperature Raman spectroscopy and the vibrational bands were fully assigned with the aid of density functional theory (DFT) calculations. The electronic structures obtained from the DFT calculations were analyzed by the quantum theory of atoms in molecules (QTAIM). The crystal structures of SF4 ⋅NC5 H5 , SF4 ⋅4-NC5 H4 (CH3 ), and SF4 ⋅4-NC5 H4 N(CH3 )2 revealed weak SN dative bonds with nitrogen coordinating in the equatorial position of SF4 . Based on the QTAIM analysis, the non-bonded valence shell charge concentration on sulfur, which represents the lone pair, is only slightly distorted by the weak dative SN bond. No evidence for adducts between quinoline or isoquinoline with SF4 was found by low-temperature Raman spectroscopy.

Pentafluoro-oxotellurate(VI) anions of mercury(II); syntheses and structures of [Hg(OTeF5)4](2-), [Hg(OTeF5)5](3-), [Hg2(OTeF5)6](2-), [Hg(OTeF5)4](2-)·Hg(OTeF5)2, and [Hg2(OTeF5)7](3-)·Hg(OTeF5)2.

Mercury(II) anions derived from the F5TeO- (teflate) group were synthesized and structurally characterized. The salts, [N(CH2CH3)4]2[Hg(OTeF5)4], [N(CH3)4]3[Hg(OTeF5)5], [N(CH2CH3)4]3[Hg(OTeF5)5], [N(CH3)4]2[Hg2(OTeF5)6], Cs2[Hg(OTeF5)4]·Hg(OTeF5)2, and {Cs3[Hg2(OTeF5)7]·Hg(OTeF5)2}·4SO2ClF, were obtained by reaction of Hg(OTeF5)2 with [M][OTeF5] (M = [N(CH3)4](+), [N(CH2CH3)4](+), Cs(+)) and were characterized by low-temperature single-crystal X-ray diffraction and low-temperature Raman spectroscopy. Unlike in the extensively fluorine-bridged solid-state structures of [HgF3](-) and [HgF4](2-), the less basic and more sterically demanding teflate ligands of the Hg(II) anions show less tendency to bridge. The anions exhibit a variety of structural motifs, ranging from well-isolated tetrahedral [Hg(OTeF5)4](2-) and square-pyramidal [Hg(OTeF5)5](3-) to the chain structures, [Hg2(OTeF5)6](2-) and [Hg2(OTeF5)7](3-)·Hg(OTeF5)2. The geometrical parameters and vibrational frequencies of [Hg(OTeF5)4](2-) (S4), [Hg(OTeF5)5](3-) (C1), and [Hg2(OTeF5)6](2-) (D2) anions, as well as the hypothetical [Hg3(OTeF5)8](2-) (C1) anion, were calculated using density functional theory methods (PBE1PBE/def2-TZVPP), which aided in the assignment of the Raman spectra of [Hg(OTeF5)4](2-), [Hg(OTeF5)5](3-), [Hg2(OTeF5)6](2-), and Cs2[Hg(OTeF5)4]·Hg(OTeF5)2. The calculated geometries were used to assess the effects of solid-state interionic interactions on the anion geometries. For the most part, the gross gas-phase trigonal bipyramidal (tbp) geometry of [Hg(OTeF5)5](3-) adheres to the predicted VSEPR geometry but contrasts with the solid-state anion structures, which have square-pyramidal geometries or geometries that lie between square pyramidal- and tbp-geometries. However, the bond length order calculated for the Hg-O bonds of tbp-[Hg(OTeF5)5](3-), Hg-Oeq > Hg-Oax, is opposite to that predicted by the VSEPR model of molecular geometry. Natural bond orbital analyses provided the associated Mayer bond orders, Mayer valencies, and natural population analysis charges.

Xenon(IV)-carbon bond of [C6F5XeF2]+; structural characterization and bonding of [C6F5XeF2][BF4], [C6F5XeF2][BF4]·2HF, and [C6F5XeF2][BF4]·nNCCH3 (n = 1, 2); and the fluorinating properties of [C6F5XeF2][BF4].

The [C6F5XeF2](+) cation is the only example of a Xe(IV)-C bond, which had only been previously characterized as its [BF4](-) salt in solution by multi-NMR spectroscopy. The [BF4](-) salt and its new CH3CN and HF solvates, [C6F5XeF2][BF4]·1.5CH3CN and [C6F5XeF2][BF4]·2HF, have now been synthesized and fully characterized in the solid state by low-temperature, single-crystal X-ray diffraction and Raman spectroscopy. Crystalline [C6F5XeF2][BF4] and [C6F5XeF2][BF4]·1.5CH3CN were obtained from CH3CN/CH2Cl2 solvent mixtures, and [C6F5XeF2][BF4]·2HF was obtained from anhydrous HF (aHF), where [C6F5XeF2][BF4]·1.5CH3CN is comprised of an equimolar mixture of [C6F5XeF2][BF4]·CH3CN and [C6F5XeF2][BF4]·2CH3CN. The crystal structures show that the [C6F5XeF2](+) cation has two short contacts with the F atoms of [BF4](-) or with the F or N atoms of the solvent molecules, HF and CH3CN. The low-temperature solid-state Raman spectra of [C6F5XeF2][BF4] and C6F5IF2 were assigned with the aid of quantum-chemical calculations. The bonding in [C6F5XeF2](+), C6F5IF2, [C6F5XeF2][BF4], [C6F5XeF2][BF4]·CH3CN, [C6F5XeF2][BF4]·2CH3CN, and [C6F5XeF2][BF4]·2HF was assessed with the aid of natural bond orbital analyses and molecular orbital calculations. The (129)Xe, (19)F, and (11)B NMR spectra of [C6F5XeF2][BF4] in aHF are reported and compared with the (19)F NMR spectrum of C6F5IF2, and all previously unreported J((129)Xe-(19)F) and J((19)F-(19)F) couplings were determined. The long-term solution stabilities of [C6F5XeF2][BF4] were investigated by (19)F NMR spectroscopy and the oxidative fluorinating properties of [C6F5XeF2][BF4] were demonstrated by studies of its reactivity with K[C6F5BF3], Pn(C6F5)3 (Pn = P, As, or Bi), and C6F5X (X = Br or I).