The reaction of [Ph(3)C](2)[B(12)Cl(12)] with R(3)SiH (R = Me, Et, iPr) in 1,2-difluorobenzene yielded the corresponding silylium compounds (R(3)Si)(2)B(12)Cl(12) containing the weakly coordinating dianion [B(12)Cl(12)](2-). The products were fully characterized by IR and Raman spectroscopy and by multinuclear ((1)H, (11)B, (13)C, (29)Si) NMR spectroscopy in solution and the solid state (magic angle spinning). (Et(3)Si)(2)B(12)Cl(12) and (iPr(3)Si)(2)B(12)Cl(12) were characterized by X-ray diffraction. In the solid state, the silylium cations are coordinated to the [B(12)Cl(12)](2-) anion via silicon-chlorine contacts, which are significantly shorter than the sum of the van der Waals radii. Two different coordination patterns were found. The [Et(3)Si](+) cations are coordinated to chlorine atoms of [B(12)Cl(12)](2-) in the 1 and 12 positions, while the [iPr(3)Si](+) cations coordinate to chlorine atoms in the 1 and 7 positions. The 1,12 regioisomer is calculated [for (Me(3)Si)(2)B(12)Cl(12)] to be favored over the 1,7 isomer by only 8 kJ mol(-1), indicating that packing effects may cause the difference. The silylium cations are very reactive and bind to every Lewis base, being stronger than the aromatic solvent (e.g., benzene, 1,2-difluorobenzene, etc.) used. Consequently, three different crystal structures containing cationic Lewis acid-base complexes [iPr(3)Si-donor](+) were obtained from preparations of (iPr(3)Si)(2)[B(12)Cl(12)]. The presence of traces of water leads to crystals of [iPr(3)Si(OH(2))](2)[B(12)Cl(12)] containing the protonated silanol [iPr(3)Si(OH(2))](+), which is only the second example of its kind. Structures containing the [iPr(3)SiOS(H)OSiiPr(3)](+) cation were obtained from the reaction of [Ph(3)C](2)[B(12)Cl(12)].2SO(2) with an excess of iPr(3)SiH in 1,2-difluorobenzene. [iPr(3)SiOS(H)OSiiPr(3)](2)[B(12)Cl(12)] and [iPr(3)SiOS(H)OSiiPr(3)][(iPr(3)Si)B(12)Cl(12)] were structurally characterized by X-ray diffraction. On the basis of the structural data and quantum chemical calculations, the crystallographically invisible hydrogen atom bound to the sulfur atom was identified. A comparison of the weakly coordinating dianion [B(12)Cl(12)](2-) with the widely applied corresponding chlorinated carboranes based on several criteria including the nu(N-H) scale established the dianion [B(12)Cl(12)](2-) to be as weakly coordinating as the single negatively charged carboranes.

Single crystals of dark-red MgB(7) were grown from the elements in a Cu-melt. The crystal structure (Pearson symbol oI64; space group Imma; a = 10.478(2) Å, b = 5.977(1) Å, c = 8.125(2) Å, 2842 reflns, 48 params, R(1)(F) = 0.018, R(2)(I) = 0.034) consists of a hexagonal-primitive packing of B(12)-icosahedra and B(2)-units in trigonal-prismatic voids. According to the UV-vis spectra and band structure calculations MgB(7) is semiconducting with an optical gap of 1.9 eV. The long B-B distance of 2.278 Å within the B(2)-unit can be seen as a weak bonding interaction. The new Mg(∼5)B(44) occurs beside the well-known MgB(12) as a byproduct. Small fragments of the black crystals are dark-yellow and transparent. The crystal structure (Pearson symbol tP196, space group P4(1)2(1)2, a = 10.380(2) Å, c = 14.391(3) Å, 4080 reflns, 251 params, R(1)(F) = 0.025, R(2)(I) = 0.037) is closely related to tetragonal boron-II (t-B(192)). It consists of B(12)-icosahedra and B(19+1)-units. With a charge of -6 for the B(19+1)-units and a Mg-content of ∼20 Mg-atoms per unit cell the observed Mg content in Mg(∼5)B(44) is quite close to the expected value derived from simple electron counting rules. All compositions were confirmed by EDXS. The microhardness was measured on single crystals for MgB(7) (H(V) = 2125, H(K) = 2004) and MgB(12) (H(V) = 2360, H(K) = 2459).

Transparent and nearly colorless single crystals of r-LiB 13 C 2 were obtained by reaction of boron with Li 2 CO 3 in a Cu melt at 1250-1300°C. The structure analysis [R3m, a = 5.6535(1), c = 12.5320(2) Å, 421 independent reflections, 22 parameters, R 1 = 0.034, wR 2 = 0.093] revealed a crystal structure that can be described as a filling variant of rhombohedral B 13 C 2 . Li + is located in a void above or below the linear CBC unit. The site occupation is close to 50 % resulting in an electron-precise composition according to Wade's rules if a positive charge is given to the CBC entity: Li + (B 12 ) 2-(CBC) + . The displacement parameters of the CBC unit indicate disorder in the [001] ARTICLE Results and Discussion Crystal StructureSingle crystals of r-LiB 13 C 2 can be selected from other products like Li 2 B 12 C 2 and o-LiB 13 C 2 based on their shape (Figure 1). Li 2 B 12 C 2 forms well-developed rods or bricks, and o-LiB 13 C 2 was obtained as less or more regular hexagonal platelets. In contrast to this, the shapes of crystals of r-LiB 13 C 2 are very irregular. Powdered samples of r-LiB 13 C 2 are of lightgreen color. Interestingly, r-LiB 13 C 2 is only formed if Li 2 CO 3 is used as starting material, being a source for both lithium and carbon. In contrast to this, o-LiB 13 C 2 and the more stable Li 2 B 12 C 2 were obtained from syntheses with elemental Li and C and Sn as an auxiliary metal. [3]

We present synthesis, crystal structure, hardness, and IR/Raman and UV/Vis spectra of a new compound with the mean composition LiB(12)PC. Transparent single crystals were synthesised from Ga, Li, B, red phosphorus and C at 1500 °C in boron nitride crucibles welded in Ta ampoules. Depending on the type of boron used for the synthesis we obtained colourless, brown and red single crystals with slightly different P/C ratios. Colourless LiB(12)PC crystallizes orthorhombic in the space group Imma (No. 74) with a=10.188(2) Å, b=5.7689(11) Å, c=8.127(2) Å and Z=4. Brown LiB(12)P(0.89)C(1.11) is very similar, but with a lower P content. Red single crystals of LiB(12)P(1.13)C(0.87) have a larger unit cell with a=10.4097(18) Å, b=5.9029(7) Å, c=8.2044(12) Å. EDX measurements confirm that the red crystals contain more phosphorus than the other ones. The crystal structure is characterized by a covalent network of B(12) icosahedra connected by exohedral B-B bonds and P-P, P-C or C-C units. Li atoms are located in interstitials. The structure is closely related to MgB(7), LiB(13)C(2) and ScB(13)C. LiB(12)PC fulfils the electron counting rules of Wade and also Longuet-Higgins. Measurements of Vickers micro-hardness (H(V)=27 GPa) revealed that LiB(12)PC is a hard material. The optical band gaps obtained from UV/Vis spectra match the colours of the crystals. Furthermore we report on the IR and Raman spectra.

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