Temperature Dependence of ²H Nuclear Quadrupole Interaction in Very Short Hydrogen Bonds in Some Organic Acidic Salt Crystals

Abstract

The 2 H nuclear quadrupole interaction parameters, 2 and , are closely related to the shape of the potential energy surface at hydrogen bonds and depend sensitively on their geometry. We measured the temperature dependence of the 2 H NMR spectra of the crystalline acidic salts KDCO 3 , KD acetylenedicarboxylate, RbD acetylenedicarboxylate, and KD maleate, which contain very short O-D O type hydrogen bonds. The temperature coefficient decreases with increase in the O O distance in the hydrogen bond. Ab inito molecular orbital calculations of the electric field gradient tensor based on the temperature dependent structure of each crystal indicate that thermal expansion of the hydrogen bond geometry is not responsible for this tendency. Ab initio calculations also predict that a fictitious off center shift of the hydrogen position in a symmetric hydrogen bond causes very high

Temperature Dependence of NMR Parameters Calculated from Path Integral Molecular Dynamics Simulations

“…21 For NMA, however, a 6.9 kHz increase was observed when the temperature increased from 200 to 300 K. 44 Similar unusual temperature dependence of quadrupolar couplings has also been reported for other systems with short hydrogen bonds. 45,46 Previous ab initio calculations, even with high-level corrections for electron correlation, did not accurately reproduce such NMR data observed in such strongly hydrogen-bonded systems. 47,48 It has been shown that a simple model based on the anharmonicity of the hydrogen bond potential fails to describe temperature dependence of quadrupolar couplings.…”