1H NMR Studies on Cationic Dynamics in Solid Methylguanidinium, 1,1-Dimethylguanidinium, 1,2,3-Trimethylguanidinium, and 1,1,3,3-Tetramethylguanidinium Chlorides

The temperature dependence of 1H NMR second moments and spin-lattice relaxation times, T1 and T1ϱ in the laboratory and rotating frames, respectively, were observed for solid methylguanidinium (MeguH+), 1,1-dimethylguanidinium (1,1-Me2guH+), 1,2,3-trimethylguanidinium (1,2,3-Me3guH+), and 1,1,3,3-tetramethylguanidinium (1,1,3,3-Me4guH+) chlorides. Phase transitions were found for (1,1-Me2guH)Cl and (1,2,3-Me3guH)Cl at 400 and 409 K, respectively, which were confirmed by differential thermal analysis experiments. Below room temperature, rapid C3 reorientational motions of CH3 groups were detected for the all cations in the above crystals. The activation energy for the motion of each CH3 group in the cations was evaluated. Above room temperature, the temperature dependences of T1ϱ were determined against T−1 for (1,1-Me2guH)Cl, (1,1,3,3-Me4guH)Cl, and their partially deuterated (NH2 ND2) analogs. For these salts, 1H T1ρ minima were observed and could be interpreted as arising from the 180° flip motions of the NMe2 group and also of the whole cation for (1,1-Me2guH)Cl and its deuterated analog about the C+—NMe2 axis of the cations, and the whole cationic 180° flip motion about the C+—NH2 or C+—ND2 bond axis of the cation for (1,1,3,3-Me4guH)Cl or its deuterated analog, respectively, in addition to the NMe2 180° flip motions.

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