Relaxation resulting from the modulation of dipolar interaction the quadrupolar interaction. It has been shown that, for 2 H is commonly used for estimating distances in molecules in soluand 23 Na in single crystalline solids, the transitions 0m } tions. However, for most nuclei with spin I ΓΊ 1 2 the single-quantumm are affected to the first order by the dipolar interaction transition relaxation by dipolar interaction is masked by quadru-(1, 2) while the other transitions are dominated by the quadpolar relaxation. In the present study, it is shown that even in rupolar interaction. The measurements of transitions where systems where single-quantum relaxation times are dominated by Dm ΓΊ 1 were made possible by the development of multiplequadrupolar interaction, dipolar relaxation can be measured by quantum-filtering (MQF) techniques (3, 4). It was shown following the 0m } m transitions. This is demonstrated for 7 Li in by Jaccard et al. (5) that MQF measurements are also possithe complex [Li-Kryptofix 211] / X 0 (X Γ
Cl, Br) dissolved in ble for half-integer spins in solution, if the motion is suffiglycerol at temperatures for which slow motion prevails and no
ciently slow, i.e., vt c ΓΊ 1. The present study shows theoreti-1 H-7 Li NOE can be observed. The relaxation times that are most important for the assessment of the dipolar interaction of 7 Li are cally and experimentally that, for such solutions, it is also
2 and they are measured by multiple-quantumtrue that the relaxation rates of the transitions 0m } m filtration techniques. For estimating the quadrupolar interaction, are dominated by the dipolar interaction. Furthermore, the the relaxation times of the populations and those of the transitions dipolar interaction can be assessed from these relaxation { 1 2 } { 3 2 were measured. The longitudinal and transverse relaxrates whereas the NOE is too small to be adequate for such ation times of 6 Li as well as the 1 H-6 Li NOE were also measured an assessment. The theory for the relaxation mechanism by and, together with the 7 Li measurements, were used to obtain the dipolar interaction is developed for any spin with I ΓΊ 1 2 , and strengths of dipolar (D) and quadrupolar ( x) interactions. The it is tested by measurements of single-and multiple-quantum experimental data were analyzed using several models to describe relaxation times of 7 Li (I Γ
3 2 ).
the motion. The model that gave the best fit and resulted in parameters that were physically meaningful encompassed a whole-body isotropic motion as well as internal anisotropic motion. For this THEORY particular model, the following values for the quadrupolar and the dipolar interactions strength were obtained: D( 7 Li)/2p Γ
6.8
The spin dynamics under the effect of the quadrupolar kHz, x( 7 Li)/2p Γ
85 kHz and D( 6 Li)/2p Γ
1.4 kHz, x( 6 Li)/2p Γ
interaction has been given in great detail in the literature for 2.6 kHz. From the value of D, an estimate of the average lithiumisotropic as well as anisotropic motion for 1 Β£ I Β£ 7 2 (5proton distance was calculated to be 3.3 A Λ, which is in fair agree-9). In multiple-pulse experiments on isotropic media, evenment with crystallographic studies. The sizes of the quadrupolar rank tensors are not formed unless cross correlations between and dipolar interactions were independently confirmed by the 7 Li quadrupolar and dipolar (or dipolar and dipolar) (10-12) NMR powder spectra of the complexes that were used for the interactions are significant or, as shown in Appendix A, the solution studies.