LI-7 SOLID-STATE NMR OF LITHIUM AMIDES - STRUCTURAL INFORMATION FROM LI-7 QUADRUPOLAR COUPLING-CONSTANTS

Lithium-7 quadrupolar coupling constants, chi(Li-7), were measured for a number of microcrystalline lithium amides by solid-state Li-7 magic angle spinning (MAS) NMR. A linear correlation between chi(Li-7) and the structural N-Li-N angle known from x-ray diffraction work was foun d: chi(Li-7)=(4.1 +/- 0.5) not less than N-Li-N - (110.8 +/- 69.0). On this basis, structural information for new systems becomes available. For the polymer material [H2C(CH2)(3)NLi](n) a ladder structure is pr oposed. The pi-flip of the five-membered metallacycle formed by the co ordination of tetramethylethylenediamine (TMEDA) with lithium in [(H2C (CH2)(3)NLi)(2) . TMEDA](2) was detected by C-13 cross-polarization/MA S DNMR spectroscopy. From the analysis of the temperature-dependent li neshape of the methyl signals, a barrier of Delta G(not equal)(293) = 66 kJ mol(-1) was derived for this rotational process in the solid, wh ich compares favourably with data derived for related compounds. (C) 1 998 John Wiley & Sons, Ltd.