Konrad Seppelt

Crystal and Molecular Structures of Hexamethyltungsten and Hexamethylrhenium

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 C3v 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.

Preparation and Structure of F3As-Au+SbF6-, the Structures of Au(CO)2+ and Au(PF3)2+

AuF3, Au(SbF6)2, or [Au(SbF6)2 · Au(AuF4)2] react with AsF3 in HF/SbF5 under formation of F3As–Au+SbF6–. This is stable to about 0 °C. The crystal structure reveals strong cationic-anionic interactions through one fluorine atom so that a description as F3As–Au–F…SbF5 is also possible (a = 798.3(1), b = 912.0(2), c = 1076.3(2) pm, β = 96.25°, space group P21/n). A similar reaction with CO affords [Au(CO)2+]2SbF6– · Sb2F11– (a = 1404.8(1), b = 622.86(3), c = 1130.2(1) pm, space group Pmma). The cations in these compounds have the expected linear geometry. Reaction with PF3 affords Au(PF3)2+SbF6– (a = 825.5(2), b = 824.4(2), c = 876.4(3) pm, γ = 119.99°, space group P21/n).

Soluble Chlorofullerenes C60Cl2,4,6,8,10. Synthesis, Purification, Compositional Analysis, Stability, and Experimental/Theoretical Structure Elucidation, Including the X-ray Structure of C1-C60Cl10

The efficacy of various analytical techniques for the characterization of products of C(60) chlorination reactions were evaluated by (i) using samples of C(60)Cl(6) of known purity and (ii) repeating a number of literature syntheses reported to yield pure C(60)Cl(n) compounds. The techniques were NMR, UV-vis, IR, and Raman spectroscopy, FAB, MALDI, LDI, ESI, and APCI mass spectrometry, HPLC, TGA, elemental analysis, and single-crystal X-ray diffraction. Most of these techniques are shown to give ambiguous or erroneous results, calling into question the composition and/or purity of nearly all C(60)Cl(n) compounds reported to date. The optimum analytical method for chlorofullerenes was found to be a combination of HPLC and either MALDI or APCI mass spectrometry. For the first time, the chlorination of C(60) by ICl, ICl(3), and Cl(2) was studied in detail using dynamic HPLC analysis and APCI mass spectrometry. Suitable conditions were found for the preparation of the new chlorofullerenes 1,7-C(60)Cl(2), 1,9-C(60)Cl(2), 1,6,9,18-C(60)Cl(4), and 1,2,7,10,14,24,25,28,29,31-C(60)Cl(10). The latter compound was also studied by (13)C NMR spectroscopy and X-ray diffraction, which led to the unambiguous determination of its asymmetric addition pattern. The unusual structure of C(60)Cl(10) was compared with other possible isomers using DFT-predicted relative energies. These results, along with additional experimental data and an analysis of the DFT-predicted frontier orbitals of likely intermediates, were used to rationalize the formation of the new compound C(60)Cl(10) from C(60)Cl(6) and excess ICl without the rearrangement of any C-Cl bonds. For the first time, the stability of C(60)Cl(n) compounds under a variety of conditions was studied in detail, leading to the discovery that they are, in general, very light-sensitive in solution. The X-ray structure of C(60)Cl(6) was also redetermined with higher precision.

Isolation and Structure of the OCNCO(+) Ion.

Strongly bent at the nitrogen atom (130.7 degrees ), 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.

The Structure of Carbon Suboxide, C3O2, in the Solid State

Carbon suboxide, C3O2, is crystallized from the melt. According to the X-ray structure determination the crystal contains two non-crystallographically equivalent molecules in the asymmetric unit: a = 986.9(2), b = 1206.0(2), c = 516.0(1) pm, space group Pnma. Both molecules are linear. A close inspection of the vibrational amplitudes indicates some systematic deviations from linearity. Die Struktur des OCCCO im festen Zustand Kohlenstoffsuboxid, C3O2, wurde aus der Schmelze auskristallisiert. Die Kristallstruktur ist aus zwei kristallographisch verschiedenen Molekulen aufgebaut. a = 986.9(2), b = 1206.0(2), c = 516.0(1) pm, Raumgruppe Pnma. Beide Molekule sind linear. Eine genaue Analyse der Schwingungsellipsoide deutet auf systematische Abweichungen von der Linearitat hin.

Pentafluoro-λ6-sulfanylacetylene complexes of cobalt

Abstract The reaction of Co2(CO) 8 with RCCSF 5 gives 1 : 1, 1 : 2, and 1 : 3 type products, depending on R. For R = H all three products can be isolated. According to the single-crystal structure determinations, the 1 : 1 product has the known di-cobaltatetrahedrane structure, the 1 : 2 product is a cobaltacyclopentadiene cobalt, whereas the 1 : 3 product has been previously identified as a “fly-over bridge” complex. Sterically more crowded F 3 CCCSF 5 and C 6 H 5 CCSF 5 give only the 1 : 1 reaction. The product of F 3 CCCSF 5 reacts further with HCCSF 5 to a 1 : 3 product, made up of different alkyne molecules.

Isolation and structural and electronic characterization of salts of the decamethylferrocene dication

Charging up the iron in ferrocene salts Ferrocene is the archetype of the sandwich compounds, so called because a metal atom is inserted between two carbon rings. The elucidation of ferrocenes structure was pivotal to the development of organometallic chemistry during the mid-20th century. The ease with which the iron in the center of the molecule can toggle between the +2 and +3 oxidation states has made the compound a common electrochemical standard. Malischewski et al. report the synthesis and isolation of ferrocene salts with iron in the +4 state, which they characterize crystallographically and spectroscopically. Science, this issue p. 678 An archetypal organometallic compound has been isolated in a higher oxidation state. Ferrocene and its decamethyl derivative [Cp*2Fe] are the most common standards for nonaqueous electrochemical investigations because of their well-defined and only mildly solvent-dependent reversible Fe(II)/Fe(III) redox couple. Higher oxidation states have only rarely been studied. We report the isolation and crystallographic and spectroscopic characterization of surprisingly stable Fe(IV) salts of the [Cp*2Fe]2+ dication, produced by oxidation of [Cp*2Fe] with AsF5, SbF5, or ReF6 in neat sulfur dioxide as well as [XeF](Sb2F11) in neat hydrogen fluoride. The Sb2F11– salt exhibits a metallocene with the expected mutually parallel arrangements of the Cp* rings, whereas the As2F11–, AsF6–, SbF6–, and ReF6– salts manifest tilt angles ranging from 4° to 17°. Both 57Fe Mössbauer spectroscopy and superconducting quantum interference device magnetization studies reveal identical d-orbital splitting with an S = 1, 3E ground state based on the 3d electronic configuration e2g3a1g1 of all [Cp*2Fe]2+ salts.

Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6(CH3)6 2+

In contrast to the well-known 2-norbornyl cation, the structure of which was a matter of long debate until its pentacoordinated nature was recently proven by an X-ray structure, the pentagonal-pyramidal dication of hexamethylbenzene has received considerably less attention. This species was first prepared by Hogeveen in 1973 at low temperatures in magic acid (HSO3 F/SbF5 ), for which he proposed a non-classical structure (containing a hexacoordinated carbon) based on NMR spectroscopy and reactivity studies, but no X-ray crystal structure has been reported. C6 (CH3 )62+ can be obtained through the dissolution of hexamethyl Dewar benzene epoxide in HSO3 F/SbF5 and crystallized as the SbF6- salt upon addition of excess anhydrous hydrogen fluoride. The crystal structure of C6 (CH3 )62+ (SbF6- )2 ⋅HSO3 F confirms the pentagonal pyramidal structure of the dication. The apical carbon is bound to one methyl group (distance 1.479(3) Å) and to the five basal carbon atoms (distances 1.694(2)-1.715(3) Å).

The gas phase structures of XF5NCO (X = S, Se, Te): an electron diffraction study

Abstract The geometric structures of the three title compounds have been studied in the gas phase by electron diffraction. The possibility of the cyanate structure for the selenium compound (i.e., SeF 5 OCN) has to be rejected on the basis of this study. The NC and CO bond lengths in all three compounds are longer than in other isocyanates. For the XN bond lengths in the sulphur, selenium and tellurium compounds values of 1.668(6), 1.789(6) and 1.859( A, respectively, were determined. The nitrogen bond angle is the same for the sulphur and tellurium compounds (124.9(1.2)° and 126.5(2.4)°), while this angle is smaller in SeF 5 NCO (116.9(0.8)°). The isocyanate groups are slightly tilted in the trans direction for all three compounds.

The XeCl+ Ion: [XeCl]+[Sb2F11]−

Chlorine-fluorine exchange in XeF+ leads to the orange crystalline salt [XeCl]+ [Sb2 F11 ]- , 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.