The determination of deuterium atom coordinates and nuclear quadrupole interactions in lanthanum nicotinate dihydrate crystals by Nd3+–deuterium double resonance

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Abstract
We have obtained the ENDOR (electron nuclear double resonance) spectra of the four deuterons of the two D2O molecules coordinated to Nd3+ dilutely substituted for La3+ in La2(C5H4NCO2)6 (D2O4)4 (dimeric lanthanum nicotinate dihydrate) molecules in single crystals. From the measurements of the values of the anisotropic magnetic hyperfine interactions between Nd3+ and the deuterons we have determined the coordinates of the deuterons in the principal axis system of the Nd3+ Zeeman interaction with average standard deviation, 0.011 Å. We have made detailed comparisons of the ENDOR values of the coordinates with values determined by x‐ray diffraction. We have also obtained the values of the quadrupole coupling constants, asymmetry parameters, and directions of the principal axes of the electric field gradient tensors at each deuteron site. The analysis of the magnetic hyperfine and electric quadrupole interactions in relation to water molecule geometry, orientations of water molecules, hydrogen bond lengths, and isotope effects in hydrogen bonding, is discussed. Comparisons are made with earlier ENDOR results for the same molecule with H2O coordinated to the metal ion.

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