Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6 (CH3 )62.

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).

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

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 (57)Fe Mössbauer spectroscopy and superconducting quantum interference device magnetization studies reveal identical d-orbital splitting with an S = 1, (3)E ground state based on the 3d electronic configuration e2g (3)a1g (1) of all [Cp*2Fe](2+) salts.

Trigonal-prismatic versus octahedral molecular structures in [CH3)nMX6-n]] compounds.

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.

Xenon as a complex ligand: the tetra xenono Gold(II) cation in AuXe(4)2+(Sb(2)F(11)-)(2).

The first metal-xenon compound with direct gold-xenon bonds is achieved by reduction of AuF(3) with elemental xenon. The square planar AuXe(4)2+ cation is established by a single-crystal structure determination, with a gold-xenon bond length of approximately 274 picometers. The bonding between gold and xenon is of the final sigma donor type, resulting in a charge of approximately 0.4 per xenon atom.

The trifluorophosphonium ion, PF3H+, preparation and structure.

The PF3H+ ion is prepared as PF3H+.SbF6-.HF by protonation of PF3 with HF/SbF5 at low temperatures in anhydrous HF. Crystals are obtained directly from this solvent. A crystal structure determination shows the presence of a pseudo-tetrahedral PF3H+ ion with a mean P-F distance of 148.7(2) pm, a P-H distance of 122(4) pm, and a mean PF2 angle of 106.1(1) degrees. Raman spectra were recorded of PF3H+SbF6-.HF and PF3D+.SbF6-.DF and assigned with the help of ab initio calculations. AsF3 does not react with HF/SbF5, whereas SF4 forms SF3+SbF6-.HF, which is isostructural with PF3H+SbF6-.HF.

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 OC(2)F(5)(-), OCF(CF(3))(2)(-), and OCFCF(2)O(-) Anions: Preparation and Structure.

The compounds pip(+)CF(3)O(-), pip(+)CF(3)CF(2)O(-), pip(+)(CF(3))(2)CFO(-), and (CH(3))(4)N(+)OCFCF(2)O(-) (pip(+) = 1,1,3,3,5,5-hexamethylpiperidinium) are obtained from pip(+)F(-) or (CH(3))(4)N(+)F(-) and COF(2), CF(3)COF, (CF(3))(2)CO, and (COF)(2). The structures of pip(+)CF(3)CF(2)O(-), pip(+)(CF(3))(2)CFO(-), and (CH(3))(4)N(+)OCFCF(2)O(-) have been investigated by single-crystal X-ray crystallography. Crystal data are as follows: for pip(+)CF(3)CF(2)O(-), monoclinic P2(1)/c, a = 1300.7(1) pm, b = 828.0(1) pm, c = 1513.3(2) pm, beta = 110.13(1) degrees, Z = 4; for pip(+)(CF(3))(2)CFO(-), monoclinic P2(1)/c, a = 1182.2(1) pm, b = 1032.9(2) pm, c = 1459.1(1) pm, beta = 107.45(1) degrees, Z = 4; for (CH(3))(4)N(+)OCFCF(2)O(-), tetragonal P&fourmacr;2(1)/c, a = 1115.9(1) pm, c = 1377.1(1) pm, Z = 8. All anion structures are indicative of a negative hyperconjugation effect. The structure of FCOCF(2)O(-) is clearly nonsymmetric and resembles a close to planar cis oxygen configuration with one additional fluorine bound to one carbon atom. This fluorine atom is positioned slightly toward the second carbon atom, which corresponds to a movement from the asymmetric to the symmetric fluorine-bridged structure. Interionic forces seem to be responsible for this peculiar structure. These findings are compared with structures predicted by ab initio calculations.