Molecular motion in solid ammonia trimethylalane |
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Authors: | Gianina Tutoveanu Kenneth DM Harris Jens Müller |
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Institution: | a School of Chemical Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UKb Faculty of Chemistry, University of Bochum, D-44780 Bochum, Germanyc Department of Chemistry, University of Saskatchewan, 110 Science Place, Sask., Canada SK S7N 5C9 |
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Abstract: | Solid state 2H NMR has been used to study molecular motion in deuterated ammonia trimethylalane (CH3)3AlND3. From analysis of the 2H NMR lineshape between 123 and 298 K, reorientation of the -ND3 group about the molecular Al-N axis is shown to occur at a rate higher than 108 s-1, and simulation of partially relaxed 2H NMR lineshapes shows that the reorientation can be described as a 3-site 120° jump motion. From the temperature dependence of the 2H spin-lattice relaxation time, the activation energy for this motion is estimated to be 9.3±0.3 kJ mol-1. There is no evidence from either 2H or 27Al NMR data for any site-exchange between the sites occupied by the -ND3 and -CH3 groups. The anisotropy of the dynamics of (CH3)3AlND3 indicates that the orientation of the Al-N bond is highly constrained, presumably by a strong interaction between the electric dipoles of neighboring molecules. |
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