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.

In contrast to the well-known 2-norbornyl cation, the structure of which was am atter of long debate until its pentacoordinated nature was recently proven by an X-ray structure,t he pentagonal-pyramidal dication of hexamethylbenzeneh as received considerably less attention. This species was first prepared by Hogeveen in 1973 at low temperatures in magic acid (HSO 3 F/SbF 5 ), for whichh ep roposed an onclassical structure (containing ah exacoordinated carbon) based on NMR spectroscopya nd reactivity studies,b ut no Xray crystal structure has been reported. C 6 (CH 3 ) 6 2+ can be obtained through the dissolution of hexamethyl Dewar benzeneepoxideinHSO 3 F/SbF 5 and crystallized as the SbF 6À salt upon addition of excess anhydrous hydrogen fluoride.T he crystal structure of C 6 (CH 3 ) 6 2+ (SbF 6 À ) 2 ·HSO 3 Fc onfirms the pentagonal pyramidal structure of the dication. The apical carbon is bound to one methyl group (distance 1.479(3) )and to the five basal carbon atoms (distances 1.694(2)-1.715(3) ).The tetravalencyo fc arbon and the hexagonal-planar ring structure of benzene are fundamental axioms of organic chemistry,a nd were developed 150 years ago by KekulØ. [1,2] Chemists have long been fascinated by finding exceptions from these rules.S tarting in the 1960s,v alence isomers of benzene were prepared through elaborate organic syntheses, [3][4][5][6] while hypercoordinated carbon compounds entered the stage through the pioneering work of Olah on superacids and non-classical cations. [7,8] Theb onding situation in protonated methane (CH 5 + ), which is the most prominent representative of pentacoordinated carbon, is best described as a3-center 2-electron bond between H 2 and CH 3 + ,but its isolation in bulk is elusive.The replacement of hydrogen with organogold species lead to the isolation of penta-and hexacoordinated methanium salts by Schmidbaur.T hese carbido clusters,[ (Ph 3 PAu) 5 C]+ and [(Ph 3 PAu) 6 C] 2+ ,a re significantly stabilized by aurophilic interactions. [9,10] Recently,arelated structural motive has been identified in the iron-molybdenum nitrogenase cofactor, which contains hexacoordinated C 4À .[11] Taking ac ompletely different approach, Akiba and co-workers prepared formally hypercoordinated organic species through special ligand design, where an electrophilic carbon atom is intramolecularly coordinated by two/four neighboring methoxy groups. TheC À Odistances are in the range of 2.43(1)-2.45(1) and 2.641(5)-2.750(5) ,r espectively, [12,13] thus indicating only weak interactions.Instark contrast, hypercoordinated carbon with much shorter bonds can be found in carboranes. Nevertheless,t hese common structural motives of boron chemistry are only subtly changed by replacing boron with an isolobal carbon fragment. Surprisingly,e ven hexagonalplanar carbon has been considered viable (based on theoretical calculations by Exner and Schleyer) in boron compounds, for example,inC B 6 2À . [14] Recently,t he isolation of the non-classical norbornyl cation and its crystal structure ana...

Ferrocene, Cp Fe, is quantitatively protonated in a mixture of liquid HF/PF to yield [Cp FeH](PF ), which was characterized by H/ C NMR and Fe Mössbauer spectroscopy as well as single-crystal X-ray diffraction analysis. X-ray diffraction analysis at 100 K revealed a disordered, iron-coordinated hydrido ligand, which was unambiguously located by aspherical atom refinement at 100 K, and by analyzing the non-disordered crystal structure at 30 K, revealing a non-agostic structure.

One-electron oxidation of diaryldichalcogenides is the key to the preparation of the corresponding radical cations.

The reaction of AgBF4 and [Rh(COD)Cl]2 (COD=1,5‐cyclooctadiene) in presence of [NEt4][C5(CF3)5] afforded the fluorocarbon soluble complex [Rh(COD)(C5(CF3)5)] by salt metathesis. This complex represents the first example for a successful coordination of the weakly basic [C5(CF3)5]− ligand, since its first synthesis in 1980. In addition to [Rh(COD)(C5(CF3)5)] also the byproduct [Rh(COD)(C5(CF3)4H)] was isolated and fully characterized. Accompanying DFT studies showed that the interaction energy of the [C5(CF3)5]− ligand towards the 12‐electron fragment [Rh(COD)]+ is ≈70 kcal mol−1 lower in comparison to [C5(CH3)5]− due to reduced electrostatic interactions and weaker π‐donor properties of the ligand. The quantitative but reversible substitution of the [C5(CF3)5]− ligand by toluene, converting it into a weakly coordinating anion, experimentally proved the extraordinary weak bonding interaction.

The B12F12(-) radical anion was generated by oxidation of [CoCp2(+)]2B12F12(2-) with AsF5 in SO2. In the crystal structure of [CoCp2(+)]B12F12(-), the anion displays a lowered symmetry (D2h) instead of an Ih-symmetric dianion as a result of Jahn-Teller distortion. Moreover, shortening of the B-F bonds and subtle changes of the B-B bonds are observed. DFT calculations show that, for the unknown neutral B12F12, unprecedented structural isomers [e.g., octahedral B6(BF2)6] are energetically favored instead of an icosahedral structure. The structures and energetics are compared with those of the analogous chlorine compounds.

Decamethylmanganocene Cp*2Mn is reduced to its anion [Cp*2Mn]− by the potassium metal in refluxing THF.

The structures of three solvated monovalent cation salts of the superweak anion BF (Y), K(SO)Y, Ag(SO)Y, and Ag(HO)Y, are reported and discussed with respect to previously reported structures of Ag and K with other weakly coordinating anions. The structures of K(SO)Y and Ag(SO)Y are isomorphous and are based on expanded cubic close-packed arrays of Y anions with M(OSO) complexes centered in the trigonal holes of one expanded close-packed layer of B centroids (⊙). The K and Ag ions have virtually identical bicapped trigonal prism MOF coordination spheres, with M-O distances of 2.735(1)-3.032(2) Å for the potassium salt and 2.526(5)-2.790(5) Å for the silver salt. Each M(OSO) complex is connected to three other cationic complexes through their six μ-SO-κO,κO' ligands. The structure of Ag(HO)Y is unique [different from that of K(HO)Y]. Planes of close-packed arrays of anions are offset from neighboring planes along only one of the linear ⊙···⊙···⊙ directions of the close-packed arrays, with [Ag(μ-HO)Ag(μ-HO))] infinite chains between the planes of anions. There are two nearly identical AgOF coordination spheres, with Ag-O distances of 2.371(5)-2.524(5) Å and Ag-F distances of 2.734(4)-2.751(4) Å. This is only the second structurally characterized compound with four HO molecules coordinated to a Ag ion in the solid state. Comparisons with crystalline HO and SO solvates of other Ag and K salts of weakly coordinating anions show that (i) N[(SO)(1,2-CH)], BF, SbF, and Al(OC(CF)) coordinate much more strongly to Ag than does Y, (ii) SnF coordinates somewhat more strongly to K than does Y, and (iii) BCl coordinates to K about the same as, if not slightly weaker than, Y.