The perhalogenated closo-dodecaborate dianions [B12 X12 ](2-) (X=H, F, Cl, Br, I) are three-dimensional counterparts to the two-dimensional aromatics C6 X6 (X=H, F, Cl, Br, I). Whereas oxidation of the parent compounds [B12 H12 ](2-) and benzene does not lead to isolable radicals, the perhalogenated analogues can be oxidized by chemical or electrochemical methods to give stable radicals. The chemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) with the strong oxidizer AsF5 in liquid sulfur dioxide (lSO2 ) yielded the corresponding radical anions [B12 X12 ](⋅-) (X=F, Cl, Br). The presence of radical ions was proven by EPR and UV/Vis spectroscopy and supported by quantum chemical calculations. Use of an excess amount of the oxidizing agent allowed the synthesis of the neutral perhalogenated hypercloso-boranes B12 X12 (X=Cl, Br). These compounds were characterized by single-crystal X-ray diffraction of dark blue B12 Cl12 and [Na(SO2 )6 ][B12 Br12 ]⋅B12 Br12 . Sublimation of the crude reaction products that contained B12 X12 (X=Cl, Br) resulted in pure dark blue B12 Cl12 or decomposition to red B9 Br9 , respectively. The energetics of the oxidation processes in the gas phase were calculated by DFT methods at the PBE0/def2-TZVPP level of theory. They revealed the trend of increasing ionization potentials of the [B12 X12 ](2-) dianions by going from fluorine to bromine as halogen substituent. The oxidation of all [B12 X12 ](2-) dianions was also studied in the gas phase by mass spectrometry in an ion trap. The electrochemical oxidation of the closo-dodecaborate dianions [B12 X12 ](2-) (X=F, Cl, Br, I) by cyclic and Osteryoung square-wave voltammetry in liquid sulfur dioxide or acetonitrile showed very good agreement with quantum chemical calculations in the gas phase. For [B12 X12 ](2-) (X=F, Cl, Br) the first and second oxidation processes are detected. Whereas the first process is quasi-reversible (with oxidation potentials in the range between +1.68 and +2.29 V (lSO2 , versus ferrocene/ferrocenium (Fc(0/+) ))), the second process is irreversible (with oxidation potentials ranging from +2.63 to +2.71 V (lSO2 , versus Fc(0/+) )). [B12 I12 ](2-) showed a complex oxidation behavior in cyclic voltammetry experiments, presumably owing to decomposition of the cluster anion under release of iodide, which also explains the failure to isolate the respective radical by chemical oxidation.

The weakly coordinating anion [Me3 NB12 Cl11 ](-) has been prepared by a simple two-step procedure. The anion [Me3 NB12 Cl11 ](-) is easily obtained in batches of up to 20 g by chlorination of the known [H3 NB12 H11 ](-) anion with SbCl5 at about 190 °C and subsequent N-methylation with methyl iodide. Starting from Na[Me3 NB12 Cl11 ], several synthetically useful salts with reactive cations ([NO](+) , [Ph3 C](+) , and [(Et3 Si)2 H](+) ) were prepared. Full spectroscopic (NMR, IR, Raman, TGA, MS) characterization and single-crystal X-ray diffraction studies confirmed the identity and purity of the products. The thermal, chemical, and electrochemical stability as well as the basicity of the [Me3 NB12 Cl11 ](-) anion is similar to that of the structurally related weakly coordinating 1-carba-closo-dodecaborate and closo-dodecaborate anions. The facile preparation of the [Me3 NB12 Cl11 ](-) anion and its ideal chemical and physical properties make it a cheap alternative to other classes of weakly coordinating anions.

The efficiency of methylating reagents strongly depends on the weakly coordinating properties of the anion. The introduction of carborane anions [CHB 11 R 5 X 6 ] À (R = Me, Cl; X = Cl, Br) and the synthesis of the methylating agents Me(CHB 11 Me 5 X 6 ) (X = Cl, Br) by Reed was a recent breakthrough.[1] The replacement of triflate anions by the more weakly coordinating carborane anions [CHB 11 R 5 X 6 ] À (R = Me, Cl; X = Cl, Br) significantly increased the methylating power.[2] Me(CHB 11 Me 5 X 6 ) (X = Cl, Br) methylates benzene and converts alkanes into the corresponding alkyl cations with concomitant formation of methane.[ [4c] These anions are thus of great interest as weakly coordinating dianions for methylating agents and stabilization of the resulting cations.We therefore attempted to methylate the perchlorinated dodecaborate cluster [B 12 Cl 12 ] 2À and explore its properties. In a well-known reaction, methyl fluoride was treated with the Lewis acid AsF 5 in liquid sulfur dioxide at temperatures below À30 8C to give [MeOSO][AsF 6 ] [Eq. (1)], which can be subsequently used to methylate very weak donor molecules. [5]

The alkali metal salts (M = Li, Na, K, Rb, Cs) of the perchlorinated closo-dodecaborate [B(12)Cl(12)](2-) were prepared by reaction of [NEt(3)H](2)[B(12)Cl(12)] with the corresponding alkali metal hydroxide. Crystallization of M(2)[B(12)Cl(12)] from liquid sulfur dioxide gave the sulfur dioxide complexes [Li(2)(SO(2))(8)][B(12)Cl(12)], Na(2)[B(12)Cl(12)].4SO(2), K(2)[B(12)Cl(12)].8SO(2), Rb(2)[B(12)Cl(12)].4SO(2), and Cs(2)[B(12)Cl(12)].SO(2), which were characterized by single crystal X-ray diffraction. In this work structurally characterized SO(2) complexes of the alkali metal cations K(+) and Rb(+) are reported for the first time. The structure of [Li(2)(SO(2))(8)][B(12)Cl(12)] contains discrete [Li(2)(SO(2))(8)](2+) dications and [B(12)Cl(12)](2-) dianions. Born-Haber cycles based on quantum chemical calculations and estimations of lattice enthalpies for the solid state explain the stability of the discrete dication [Li(2)(SO(2))(8)](2+) in the solid state. Heavier alkali metals form three-dimensional networks containing metal-anion and metal-sulfur dioxide contacts. The crystal structures of Na(2)[B(12)Br(12)].8SO(2) and Na(2)[B(12)I(12)].8SO(2) were determined to investigate the influence of the halogen substituent on the anion. They contain similar three-dimensional network structures. Na(2)[B(12)Br(12)].8SO(2) is isostructural to K(2)[B(12)Cl(12)].8SO(2). In addition the crystal structures of the complexes Na(2)[B(12)I(12)].8SO(2).H(2)O and Na(2)[B(12)H(12)].6SO(2).2H(2)O, which contain water ligands, are reported as well. A comparison of halogenated dodecaborates [B(12)X(12)](2-) (X = F, Cl, Br, I) based on [small nu, Greek, tilde](N-H) stretching frequencies of the corresponding [Oct(3)NH](2)[B(12)X(12)] (X = F - I) salts shows that the fluorinated anion [B(12)F(12)](2-) is the least basic and the iodinated anion [B(12)I(12)](2-) is the most basic anion in this series. These findings are in agreement with those for the corresponding series of perhalogenated carboranes and are explained by the polarizability of the halogen substituent.

The oxidation of elemental sulfur in superacidic solutions and melts is one of the oldest topics in inorganic main group chemistry. Thus far, only three homopolyatomic sulfur cations ([S ] , [S ] , and [S ] ) have been characterized crystallographically although ESR investigations have given evidence for the presence of at least two additional homopolyatomic sulfur radical cations in solution. Herein, the crystal structure of the hitherto unknown homopolyatomic sulfur radical cation [S ] is presented. The radical cation [S ] represents the first step of the oxidation of the S molecule present in elemental sulfur. It has a structure similar to the known structure of [S ] , but the transannular sulfur⋅⋅⋅sulfur contact is significantly elongated. Quantum-chemical calculations help in understanding its structure and support its presence in solution as a stable compound. The existence of [S ] is also in accord with previous ESR investigations.