Temperature dependence of the effect of deuteriation on the chlorine-35 quadrupole resonance frequency in an Mg(H2O)6SnCl6 crystal

Abstract

The ³⁵Cl NQR frequencies of Mg(H₂O)₆SnCl₆ and Mg(D₂O)₆SnCl₆, and the linewidth of the FT spectrum of the former compound were measured accurately as a function of temperature between 100 and ca. 420 K. A positive temperature dependence of the resonance frequencies was observed, which is attributed to weak O—H⋯Cl hydrogen bonds. The observed frequency shift due to deuteriation was negative below 273 K and depended strongly on temperature. This is inconsistent with the general behaviour of weak hydrogen bonds in which the zero-point-energy effect of the asymmetric potential-energy curve for motion of the proton along the bond axis plays an important role. The results can be explained by taking into account the effect of deuteriation on rotational motion of the water molecules.