Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Mixed doubles: The mixed-valent dinuclear aryltellurenyl halides PhBr₂TeTePh (see picture), and RX₂TeTeR (X=ClBr, R=2,6-Mes₂C₆H₃), the monomeric 2,6-Mes₂C₆H₃TeI, and the charge-transfer complex 2,6-Mes₂C₆H₃TeI⋅⋅⋅I₂ are presented. The stability of H₃CEX (E=S, Se, Te; X=F, Cl, Br, I) as determined by ab initio methods are also discussed.

Feeling blue: Green Xe₂⁺ reacts with excess xenon under pressure to form a blue compound. According to spectroscopic measurements and theoretical calculations, the blue compound, as shown in the picture, is most likely Xe₄⁺ with a linear, symmetric structure (D_∞h).

Gemischtes Doppel: Die gemischtvalenten zweikernigen Aryltellurenylhalogenide PhBr₂TeTePh (1) (siehe Bild) und RX₂TeTeR (2: X=Cl; 3: X=Br, R=2,6-Mes₂C₆H₃), das monomere 2,6-Mes₂C₆H₃TeI (4) und der Charge-Transfer-Komplex 2,6-Mes₂C₆H₃TeI⋅⋅⋅I₂ (5) wurden hergestellt. 1–3 können als schwere Derivate der metastabilen gemischtvalenten Disulfide F₃SSF und F₃CF₂SSCF₃ gelten. Die Stabilität von H₃CEX (E=S, Se, Te; X=F, Cl, Br, I) wurde mit Ab-initio-Methoden untersucht.

Blau gemacht: Das grüne Xe₂⁺-Ion reagiert mit Xenon unter Druck zu einer blauen Verbindung. Spektroskopische Daten und Rechnungen ergeben, dass die blaue Verbindung höchstwahrscheinlich das Xe₄⁺-Ion mit linearer Struktur ist (D_∞h , siehe Bild).

Neues vom Rhenium: Die einzige bisher bekannte Rhenium-Chlor-Verbindung mit Rhenium in der Oxidationsstufe 7 war ReO₃Cl, und die Elementkombination AO₂Cl₃ (A=Nichtmetall oder Metall) war völlig unbekannt. Nun gelang die Synthese des ersten Dioxidtrichlorids: ReO₂Cl₃. Diese Verbindung liegt im Kristall als Chlor-verbrücktes Dimer und in Lösung als Monomer vor (Abbildung: Molekülstruktur des Dimers; rot Re, blau O, grün Cl).

Re-discovery: The only rhenium(VII)–chlorine compound known previously was ReO₃Cl, and chloride oxides of composition AO₂Cl₃ (A=nonmetal or metal) were completely unknown. The synthesis of ReO₂Cl₃ has now been achieved. The compound exists as a chlorine-bridged dimer (see Figure; Re red, O blue, Cl green) in the solid state, and as a monomer in solution.

Density functional calculations for [M(CH₃)F₅], [M(CF₃)F₅], [M(CH₃S)F₅], and [M(CF₃S)F₅] (M=Mo, W) show that they are expected to be nonrigid molecules, with energy barriers for the octahedral–trigonal-prismatic interchange as low as 7.2 kJ mol⁻¹. The ground state for the CH₃ and CF₃ compounds is trigonal prismatic, for the CH₃S and CF₃S compounds, (distorted) octahedral. All calculated compounds [M(C₆F₅)_nF_6−n] (M=Mo, W) have a trigonal-prismatic ground state, whereas the situation for [M(C₆H₅)_nF_6−n] (M=Mo, W) is more complex.

Calculations reveal that the octahedral–trigonal prismatic–octahedral rearrangement has particularly low-energy barriers for MoF₆, WF₆, and (hypothetical) CrF₆. Experimental evidence is obtained from the dynamic ¹⁹F NMR spectra of the derivatives CF₃CH₂OMoF₅, CF₃CH₂OWF₅, C₆F₅OMoF₅, C₆F₅OWF₅, and (CF₃)₃COWF₅. The ground-state structure of all these compounds is octahedral; at elevated temperatures the nonequivalent metal-bound fluorine atoms undergo an intramolecular exchange. The exchange mechanism could be a 3+3 or a 2+4 twist; calculations favor the 3+3 twist.

Edelgas-Liganden: Erstmals gelang die Herstellung eines Gold(I)-Xenon-Komplexes ([(F₃As)AuXe]⁺, siehe Bild) und eines Quecksilber(II)-Xenon-Komplexes. Die Synthesen gehen von Ausgangsverbindungen mit schwach koordinierten Metallionen aus und erfolgen im supersauren Medium.

Noble-gas ligands: For the first time it has been possible to prepare a gold(I) xenon complex ([(F₃As)AuXe]⁺, see picture) and a mercury(II) xenon complex. The syntheses of these compounds start from precursors with weakly coordinated metal ions and take place in a superacid medium.

Edelmetall-Edelgas-Komplexe gibt es wohl mehr, als man für möglich halten sollte. So konnten nun neben der bereits bekannten [AuXe₄]²⁺-Spezies auch die Kationen cis- und trans-[AuXe₂]²⁺ (dessen Struktur im Kristall hier als Beispiel gezeigt ist), [XeAuFAuXe]³⁺ und [AuXe₂F]²⁺ in Form ihrer [SbF₆]⁻- oder [Sb₂F₁₁]⁻-Salze hergestellt und röntgenographisch charakterisiert werden.

Complexes between precious metals and noble gases are more abundant than was initially considered likely. For example, in addition to the already known [AuXe₄]²⁺ species, the cations cis- and trans-[AuXe₂]²⁺ (whose structure is depicted), [XeAuFAuXe]³⁺, and [AuXe₂F]²⁺ have been prepared and structurally characterized by X-ray crystallography in the form of their [SbF₆]⁻ or [Sb₂F₁₁]⁻ salts.

A new, efficient synthesis of thiopyrylium tetrafluoroborate (C₅H₅S⁺ BF₄⁻) is described. It is based on the three-step sequence ethyl vinyl sulfide propargyl vinyl sulfide 2H-thiopyran C₅H₅S⁺ BF₄⁻ in an overall yield of 54%. Preparations of C₅H₅S⁺ BPh₄⁻, C₅H₅S⁺ I⁻, and C₅H₅S⁺ CF₃SO₃⁻ (TfO⁻) are also described. The latter is the subject of the first X-ray single crystal structure determination of the thiopyrylium ion.

The crystal structure of C₂H₅C(CH₂O)₃PO₃ shows that this ozonide contains a symmetric, almost planar, four-membered PO₃ ring with two crystallographically different, but otherwise essentially equal, molecules in the asymmetric unit cell.

Chlorine–fluorine exchange in XeF⁺ leads to the orange crystalline salt [XeCl]⁺[Sb₂F₁₁]⁻ (see structure), which is stable below −10°C. Thus, the number of known noble gas monohalogen cations is now three and, as calculations show, is approaching the theoretically possible limit. The synthesis of other such compounds—with the exception of ArF⁺, which remains a formidable task—seems unlikely.

The only pentafluoride with a dimeric structure is gold pentafluoride (see structure). According to calculations it has the highest fluoride-ion affinity and thus is the strongest Lewis acid known to date. It decomposes in HF under its own acidity to give AuF₃ and F₂.

Durch Fluor-Chlor-Austausch an XeF⁺ entsteht das unterhalb von −10°C stabile, orangefarbene Chlor-Xenon-Salz XeCl⁺Sb₂F₁₁⁻ (siehe Struktur im Kristall). Dies ist erst das dritte Edelgas-Monohalogen-Kation, und wie Rechnungen zeigen, dürfte die Synthese weiterer derartiger Kationen – mit Ausnahme der ArF⁺-Spezies – auch nicht gelingen.

Das einzige dimer auftretende Pentafluorid ist Goldpentafluorid (Struktur siehe Bild). Es ist nach Rechnungen die stärkste bekannte Lewis-Säure, aber in HF zerfällt es unter dem Einfluss seiner eigenen Acidität zu AuF₃ und F₂.

The molecular structures of [(CH₃)₅MoOCH₃], [(CH₃)₄Mo(OCH₃)₂], [(CH₃)₅WCl], and [(CH₃)₃WCl(OCH₃)₂] are reported. The first three structures are based on trigonal-prismatic geometry, the last one on octahedral geometry.

WF₆ reacts with HOCH₂CF₃ to form F₅W–OCH₂CF₃ and cis-WF₄(OCH₂CF₃)₂. CsF is added to F₅WOCH₂CF₃, yielding the heptacoordinated anion [F₆WOCH₂CF₃]⁻, which has a capped octahedral structure with the oxygen ligand in an equatorial position. The first step of the reaction of WF₆ with HN(CH₂CF₃)₂ results in F₅WN(CH₂CF₃)₂. Excess HN(CH₂CF₃)₂ causes deprotonation, yielding the heptacoordinated [F₅W(η²CF₃–CHN–CH₂CF₃)]⁻ anion. This can be described as a tungstaazacyclopropane derivative or a π complex between F₅W⁻ and CF₃–CHN–CH₂CF₃. The only case in which MoF₆ reacts similarly is the formation of F₅Mo–OCH₂CF₃.

Am Stickstoffatom stark abgewinkelt (130.7°) ist das OCNCO⁺-Ion (siehe Struktur), der nächste Verwandte von Kohlensuboxid OCCCO. Das lineare OCNCO⁺-Ion ist Rechnungen zufolge jedoch nur wenige kJ mol⁻¹ energiereicher.

Strongly bent at the nitrogen atom (130.7°), the OCNCO⁺ ion (see structure) is the closest relative to carbon suboxide OCCCO. According to calculations the linear OCNCO⁺ ion is only a few kJ mol⁻¹ higher in energy.

Known and unknown methyltitanium compounds such as [Ti(CH₃)₄], [Ti(CH₃)₅]⁻, [Ti₂(CH₃)₉]⁻ (structure shown), and [Ti(CH₃)_xCl_4−x] (x = 1–3) are prepared and structurally characterized. While all of these can be considered coordinatively and electronically highly unsaturated, no indication of intramolecular agostic hydrogen bonding is found.

Varying degrees of distortion from trigonal-prismatic symmetry are observed in the crystal structure determinations of the title compounds. A strongly distorted trigonal-prismatic C_3v symmetry was found for [W(CH₃)₆], a regular trigonal-prismatic symmetry for [Re(CH₃)₆], and both [Ta(CH₃)₆]⁻ and [Nb(CH₃)₆]⁻ show a slight distortion from an ideal trigonal prism. The reasons for these different distortions are discussed. The top view of [W(CH₃)₆] is shown on the right.

Abstract

The structure of hexamethyltungsten, W(CH₃)₆, was determined by x-ray single-crystal diffraction at −163°C. The molecule has a strongly distorted trigonal prismatic structure with C_3v symmetry. This irregular structure is not a result of intermolecular forces, but rather represents its true molecular structure. A similar structure, which deviates less from the ideal trigonal prismatic structure, was determined for hexamethylrhenium, Re(CH₃)₆. Although these structures violate the simplistic models used to predict the geometry of molecules, they are at least in part explainable by the molecular orbital model.