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首页> 外文期刊>Hyperfine Interactions: Journal Devoted to Research in the Border Regions of Solid State, Atomic and Nuclear Physics >~(127)I NQR and 1H NMR studies of 4-aminopyridinium tetraiodoantimonate(III); molecular motion and phase transition
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~(127)I NQR and 1H NMR studies of 4-aminopyridinium tetraiodoantimonate(III); molecular motion and phase transition

机译：〜（127）I NQR和1H NMR研究4-氨基吡啶四碘锑酸酯（III）;分子运动和相变

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摘要

The crystals of 4-NH_2PyHSbI_4 (Py = C_5H_4N) have been investigated by means of ~(127)I NQR, 1H NMR T1 and DTA. The crystals can exist in two modifications of β and α(I) at room temperatures. The α(I)-phase is a metastable state which is obtained when the stable β form is heated. The α(I)-phase undergoes a first-order type phase transition of α(I)←→ α(II) at 272 K (on heating), while the β-phase is stable down to 77 K. Four and two ~(127)I (m=±1/2←→±3/2) NQR lines have been found for the β- and α(II)-phases, respectively. One half of them is assignable to the terminal I atom(s) and the other to the bridging I atom(s) in each phase. All the resonance lines of the α(II)-phase underwent a disappearance above ca. 240 K and no resonance line was observed in the α(I)-phase. The second moment M_2 value of ~1H NMR spectra with 8 G2 at 290 K shows that the 4-NH_2PyH~+ cations reside in the rigid lattice in the β-phase. In contrast, in the α(I)-phase the cation rotates about an axis more symmetric than pseudo threefold axis. The activation energy of 21 kJ mol~(-1) was estimated for the reorientational motion in the α(I)-phase from the ~1HNMR T_1 measurements. The nature of phase transitions in the 4-NH_2PyHSbI_4 is discussed in comparison with that in 4-NH_2PyHSbBr_4.
机译：已通过〜（127）I NQR，1H NMR T1和DTA研究了4-NH_2PyHSbI_4（Py = C_5H_4N）的晶体。在室温下，晶体可以β和α（I）两种形式存在。 α（I）相是亚稳态，当稳定的β形式被加热时获得。 α（I）相在272 K（加热时）经历α（I）←→α（II）的一阶类型相变，而β相在低至77 K时稳定。4和2〜已经发现分别针对β相和α（II）相的（127）I（m =±1/2←→±3/2）NQR线。在每一相中，它们的一半可分配给末端I原子，另一部分可分配给桥接I原子。 α（II）相的所有共振线都在ca之上消失。 240 K，在α（I）相中未观察到共振线。在290 K下8 G2的〜1H NMR谱图的第二矩M_2值表明4-NH_2PyH〜+阳离子驻留在β相的刚性晶格中。相反，在α（I）相中，阳离子围绕比伪三重轴对称的轴旋转。根据〜1HNMR T_1测量，估计了α（I）相中方向性运动的21 kJ mol〜（-1）的活化能。与4-NH_2PyHSbBr_4中的相变性质进行了讨论。

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