Temperature dependence of hydrogen bond structure by ^2D NMR.

许多“氢盐”与没有被金属离子取代的酸性氢形成短氢键。在这种短氢键中，键长和核四极耦合常数（QCC）的取值各不相同，它们之间的关系并不简单。这与控制氢键行为的势能面变化有关。随着氢键长度的减小，其最小形状由双最小形状变为单最小形状。然而，这些区别往往难以解释氢键的静态和动态性质。在一些极短氢键中，QCC随温度的升高而升高，而不是随温度的降低而升高。QCC的温度依赖性不仅改变了它的绝对值，而且改变了它的符号，可以很好地指示氢键的性质。但只有少数观察结果存在。为了进行更详细的讨论，我们利用上年制作的仪器，观察了R_∞=2.445 Å的乙炔二羧酸单钾盐（ADCAKH）和R_∞=2.449 Å的单铷盐（ADCARbH）的二维核磁共振波谱的温度依赖性。在这两种氢盐中，QCC随温度的升高而线性增加。两种盐的温度系数基本相同，但ADCARbH的QCC绝对值大于ADCAKH，其顺序与氢键长度相同。如果氢键长度越长导致QCC值越大，则QCC值随温度升高而增大可以解释为氢键热膨胀的影响。另一方面，在r_∞~ 2.61 Å ^的碳酸氢钾中，二维核磁共振光谱显示QCC略有下降，其温度系数很小。在KDCO_3中，OH键具有单键特征，因此，由于OH键的非谐波振动激发导致的平均效应主导了QCC的温度依赖性。

Many kinds of "hydrogen salt" make short hydrogen bonds with acidic hydrogen that is not substituted by metal ions. In such short hydrogen bonds, bond length and nuclear quadrupole coupling constant (QCC) have various values and their relation is not simple. This fact has been related to the change of potential energy surface that dominates the behavior of hydrogen bond. It becomes symmteric from asymetric, and its shape changes from double to single minimum shape with decreasing hydrogen bond length. However these distinctions is often difficult to account for both static and dynamic properties of hydrogen bond. In some very short hydrogen bond QCC increases with increasing temperature contrary to normal decreasing temperature dependence of QCC.Temperature dependence of QCC could be a good indicator of the nature of hydrogen bond because it varies not only its absolute value but also its sign. But a few observations was only exist. To proceed more detailed discussion, weUsing apparatus made in previous year, temperature dependences of 2D NMR spectra of acetylenedicarboxylic acid mono potassium salt (ADCAKH) with R_∞=2.445 Å and mono rubidium salt (ADCARbH) with R_∞=2.449 Å was observed. In both hydrogen salts, QCC increases linearly with increasing temperature. The temperature coefficients of both two salts are almost same, but the absolute value of QCC of ADCARbH is more than of ADCAKH in same order as their hydrogen bond length. If longer hydrogen bond length causes more QCC value, increase of QCC with increasing temperature would be explainable as an effect of thermal expansion of hydrogen bond.On the other hand, in potassium hydrogen carbonate with r_∞〜2.61 Å ^2D NMR spectra show slight decrease of QCC, and its temperature coefficient is very small. In KDCO_3, OH bond has a single bond character, therefore averaging effect due to anharmonic vibrational excitation of OH bond dominates the temperature dependence of QCC.