Deuteron Magnetic Resonance Study of Some Crystals Containing an O—D···O Bond

A deuteron magnetic resonance study was made on four compounds with an O—D···O hydrogen bond of different strengths. The deuteron quadrupole coupling constant eqQ, asymmetry parameter η, and the directions of the field gradient tensor were determined. The eqQ and η obtained are: $$\begin{array}{cc}{\mathrm{KDCO}}_3& \text{154.4±0.6\hspace{0.17em}}\mathrm{kc/sec}\text{,0.194±0.018,}\\ (\mathrm{COOD}{)}_{2}2{\mathrm{D}}_2\mathrm{O}& \end{array}$$ $$\begin{array}{cc}{\mathrm{D}}_1(\mathrm{water})& \text{230.3±2.0\hspace{0.17em}}\mathrm{kc/sec}\text{,0.062±0.006,}\\ {\mathrm{D}}_2(\mathrm{water})& \text{219.1±2.0\hspace{0.17em}}\mathrm{kc/sec}\text{,0.16±0.03,}\end{array}\}\mathrm{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}(}\mathrm{at}{\text{−70}}^{\circ }\mathrm{C})$$ $$\begin{array}{ccc}\mathrm{\hspace{0.17em}\hspace{0.17em}}{\mathrm{D}}_1\hspace{0.17em}\mathrm{and}\hspace{0.17em}{\mathrm{D}}_2& \text{121±3\hspace{0.17em}}\mathrm{kc/sec}\text{,0.93±0.02,}& (\mathrm{at}{\text{\hspace{0.17em}67}}^{\circ }\mathrm{C})\\ \mathrm{\hspace{0.17em}\hspace{0.17em}}{\mathrm{D}}_3(\mathrm{carboxyl})& \text{139.2±0.8\hspace{0.17em}}\mathrm{kc/sec}\text{,0.098±0.005,}& \\ {\mathrm{ND}}_4{\mathrm{D}}_2{\mathrm{PO}}_4\mathrm{\hspace{0.17em}(}\mathrm{acid\; D})& \text{119.6±0.8\hspace{0.17em}}\mathrm{kc/sec}\text{,0.053±0.008,}& \\ \mathrm{K,\; D-maleate}& \text{\hspace{0.17em}56.0±0.8\hspace{0.17em}}\mathrm{kc/sec}\text{,0.53±0.07.}& \end{array}$$ The results are discussed in relation to the crystal structure in each case. It was found that the oxalic acid dihydrate crystal used was a new modification, different from the ordinary one. Reorientational motion of a water molecule similar to that in other hydrated crystals was observed in oxalic acid dihydrate from the measurement at different temperatures. A barrier to this motion of 10.0 kcal/mole was determined from the temperature dependence of the linewidth. In each compound studied, correlation between the principal axis directions of the field‐gradient tensor and the local atomic arrangement in the crystal can be readily observed. The direction of the largest principal component of the field gradient tensor is in good agreement with the O—D direction or the O—D···O direction. The direction of the second principal component is generally in good agreement with the normal to the plane defined by [Complex chemical formula] The deviation from the latter rule can be seen in D₁ of oxalic acid dihydrate where O—D···O differs greatly from a straight bond. A marked decrease of eqQ with increasing hydrogen‐bond strength is observed. Both the field gradient and the square of the OH stretching frequency as a function of O···O distance are in fairly good agreement with each other, similar to the near equality of the field gradient and force constant in diatomic hydrides. The change in the electronic contribution to the field gradient with O–H distance in the hydrogen bonded system is estimated.