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

Abstract

Molecular Dynamics / Phase TransitionsThe temperature dependence of 'H NMR second moments and spin-lattice relaxation times, Tl and TI, in the laboratory and rotating frames, respectively, were observed for solid methylguanidinium (MeguH +), 1,l-dimethylguanidinium (1,l -MezguH +), 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,l-MezguH)Cl and (1 ,2,3-Me3guH)C1 at 400 and 409 K, respectively, which were confirmed by differential thermal analysis experiments. Below room temperature, rapid C, reorientational motions of CH, groups were detected for the all cations in the above crystals. The activation energy for the motion of each CH, group in the cations was evaluated. Above room temperature, the temperature dependences of Ti, were determined against T -' for (l,l-MezguH)C1, (1,1,3.3-Me4guH)C1, and their partially deuterated (NH2 + ND2) analogs. For these salts. 'H T,, 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 (l.l-Me2guH)C1 and its deuterated analog about the C+-NMe2 axis of the cations, and the whole cationic 1 8 0 flip motion about the C' -NH, or C' -ND, bond axis of the cation for (1,1,3,3-Me4guH)C1 or its deuterated analog, respectively, in addition to the NMez 1 8 0 flip motions. Spectroscopy, Nuclear Magnetic Resonance