Deuteron Magnetic Resonance Study of Potassium Binoxalate

A DMR single‐crystal study of KDC₂O₄ was done. It was found that there are two equivalent pairs of identical sites per unit cell. The coupling constants and asymmetry parameters at room temperature are 115.9 ± 0.7 kc/sec and 0.175 ± 0.010, 115.8 kc/sec and 0.194 ± 0.010. The major principal axes for the EFG lie in the $\mathrm{bc}$ plane making angles of ±5° with the $c$ axis. Results are consistent with placing the deuteron on certain O–O line segments between neighboring oxalate groups, thus resolving a previous uncertainty. The coupling constant fits an empirical functional relation of coupling constants versus O–O bond lengths. The values are much closer to the theoretical value obtained by Weissmann than to that of Bersohn. The coupling constant increased from 114.1 to 120.2 kc/sec in the range −37.3– + 137.7°C. Such an increase is rare; it may be due to vibration of the deuteron along the O–D···O bond or to thermal expansion of the crystal.