Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

Abstract

(1)H, (19)F, and (7)Li pulsed gradient spin-echo (PGSE) NMR measurements for a series of salts are reported. The (7)Li is shown to complement the (1)H and (19)F measurements; however, the use of higher concentrations (for the less-sensitive (7)Li) can lead to aggregation. For all of the salts discussed {Li(BF(4)); (n-Bu(4)N)(BF(4)), a trinuclear Ru cluster; [Ir(1,5-COD)(4)](BF(4)), where 4 is a chiral P,N ligand; and the crown ether stabilized potassium salt, [K(18-crown-6)(NPh(2))], 6}, the use of THF seems to promote strong ion pairing. In several cases, the degree of ion pairing approaches 100%. In THF solution, the potassium salt, 6, prefers to exist as a more classical ion pair rather than as the pi complex found in the solid state. In some cases, (1)H, (1)H NOESY and (1)H, (19)F HOESY spectra help to pinpoint the cation/anion spatial relationship.

Applications of NMR diffusion methods with emphasis on ion pairing in inorganic chemistry: a mini‐review

“…The small ruthenium (η 6 ‐p‐cymene) cluster, 5 , shown in Scheme , offers a good example of the multinuclear diffusion approach. All three D‐values ( 1 H, 19 F and 7 Li) were found to be identical, indicating a strong interaction between the BF 4 − and the lithium cation, which, in turn, is buried in the oxyanion cluster …”

“…D ( 7 Li) = 8.26; D ( 19 F) = 8.22; D (H) = 8.22. Values are ×10 −10 m 2 s −1 . Right: Crown ether potassium anilide salt, 6 .…”

“…For salts in which NOE probes are present in both the cation and anion, such as the crown ether potassium anilide salt, 6 , in Scheme , NOE contacts can help to refine the structure of the ion pair . For 6 , the structure shown represents that from X‐ray data; however, the solution structure, based on NOE contacts, is more classical in that the η 6 ‐bound arene is no longer coordinated to the potassium ion.…”

Structure, Formation, and Dynamics of Mo12 and Mo16 Oxothiomolybdenum Rings Containing Terephtalate Derivatives

“…[34][35][36] In this context, we applied the DOSY NMR technique to determine the nuclearity of the host-guest systems based on the anions [Mo 12 , whereby MM x stands for the molecular weight and ñ x corresponds to the specific partial volume. [37] The diffusion coefficients D x of our three compounds were measured with respect to that of [Mo 12 Trim] 3À ion [29] (MM r = 2139 g mol…”

Competitive demethylation and substitution in N,N,N-trimethylanilinium fluorides

“…Pregosin and coworkers exploited HOESY experiments to gain insight into the nature of ion pairing [43] for ammonium salts. Where tight ion pairing between an organic cation and a fluorinated anion occurs, 1 H-19 F HOESY data can also indicate the site(s) of the ion pairing interaction(s).…”