11B-NMR-Spektren von Alkyl-, Halogeno- und Rhodanohydrohexaboraten / 11B NMR Spectra of Alkyl-, Halogeno- and Rhodanohydrohexaborates

The temperature dependence of the B NMR spectra of the monosubstituted and protonated c/oso-hexaborates RB , R=CH , C , C , C C , (SCN)B and XB X = Cl. Br. I, has been determined in the range 180-300 K. The extra proton migrates at higher temperatures intramolecularly, probably across the edges of the B6 core. The extra proton is fixed to a facet of the octahedron below the coalescence temperatures 240 K (RB ) and 210 K (XB ) as recognized by the splitting of the signal of the equatorial B atoms due to the lowering of the symmetry from C to C . From the spin-spin coupling it can be deduced that the proton prefers with the softer Brönsted acids RB facets adjacent to the substituent, while with the stronger Brönsted acids XB facets including the antipodal B atom are occupied.