Nuclear Magnetic Resonance Studies of K2CuCl4·2H2O

Nuclear magnetic resonance of 35Cl in paramagnetic K2CuCl4∙2H2O has been investigated in single crystal samples at several different temperatures from 340 °K down to 4.2 °K. Zeeman splitting studies yield the two quadrupole coupling and transferred hyperfine tensors which correspond to the two inequivalent Cl ions. The quadrupole parameters at room temperature are (e2qQ/h)I = 19.05 ± 0.02 MHz, ηI = 0.183 ± 0.001 and (e2qQ/h)II = 3.262 ± 0.006 MHz, ηII = 0.945 ± 0.003. The nuclear magnetic resonance of 39K has also been investigated at room temperature. The quadrupole parameters are e2qQ/h = 0.1032 ± 0.0004 MHz and η = 0.00. The quadrupole coupling tensors for 35Cl and 39K are compared with various model calculations. The temperature dependence of the quadrupole parameters for both Cl(I) and Cl (II) can be explained by introducing a single molecular torsional motion of the rigid (CuCl4∙2H2O)2− anion. The torsional motion has an angular frequency of ~3 × 1012 rad/s around the Cu—Cl(I) bond axis. This low frequency vibration might also be involved with the anomalous temperature dependence of Cu2+ electron spin resonance previously observed in this salt.