STRUCTURAL FEATURES OF POTASSIUM AND CESIUM DODECAHYDRO-CLOSO-DODECABORATES(2-) ACCORDING TO H-1 AND B-11 NMR DATA

The structural and dynamic characteristics of the salts K2B12H12 (I) a nd Cs2B12H12 (II), containing an icosahedral closo-anion B12H122-, wer e investigated by the NMR method. Disagreement was found between the o btained NMR data and the published results from an x-ray crystallograp hic analysis with respect to the position of the H and B atoms in the crystal lattices of the compounds. The H-1 and B-11 NMR data give reas on to suppose that compounds (I) and (II) can be assigned to the quasi periodic crystal class with respect to the positions of the H and B at oms. From analysis of the line shapes in the H-1 NMR spectra the inter atomic separations r(B-H) in the B12H122- anion in the salts (I) and ( II) were determined (1.21 +/- 0.01 Angstrom). Activation dynamics char acterized by activation barriers of 54.4 and 38.9 kJ/mole respectively were obtained for the B12H122- anions.