A structural study of bis-(trimethylamine)alane, AlH3·2NMe3, by variable temperature X-ray crystallography and DFT calculations
摘要:
The structure of AlH3 center dot 2NMe(3) has been investigated by single-crystal X-ray diffraction over the range of 296-173 K. Over this temperature range a phase change is observed from Cmca to Pbcm where the methyl groups convert from a statistically disordered conformation to adopt a mutually eclipsed conformation at lower temperatures. Measurement of the unit cell dimensions shows a decrease in the lengths of the a and b axes, and an increase in that of the c axis as the temperature is lowered, with inflections apparent between 223 and 233 K in the region of the phase change. Low-temperature DSC measurements reveal the change from Pbcm to Cmca to occur at 218.3 K, with an enthalpy of 107,7 J mol(-1). The molecular structure of AlH3 center dot 2NMe(3) is compared with those of related amine adducts of Group 13 hydrides, either measured experimentally or calculated using DFT methods. H-1, C-13 and Al-27 NMR spectroscopy has also been utilized to characterize AlH3 center dot 2NMe(3) and its 1:1 counterpart AlH3 center dot NMe3. 2009 Elsevier B.V. All rights reserved.