Ligand‐Exchange Processes on Solvated Lithium Cations: DMSO and Water/DMSO Mixtures

Abstract

Solutions of LiClO(4) in solvent mixtures consisting of dimethylsulfoxide (DMSO) and water, or DMSO and gamma-butyrolactone, were studied by (7)Li NMR spectroscopy (for complexation by cryptands in gamma-butyrolactone as a solvent, see: E. Pasgreta, R. Puchta, M. Galle, N. J. R. van Eikema Hommes, A. Zahl, R. van Eldik, J. Incl. Phen., 2007, 58, 81-88). Chemical shifts indicate that the Li(+) ion is coordinated by four DMSO molecules. In the binary solvent mixture of water and DMSO, no selective solvation is detected, thus indicating that on increasing the water content of the solvent mixture, DMSO is gradually displaced by water in the coordination sphere of Li(+). The ligand-exchange mechanism of Li(+) ions solvated by DMSO and water/DMSO mixtures was studied using DFT calculations. Ligand exchange on [Li(DMSO)(4)](+) was found to follow a limiting associative (A) mechanism. The displacement of coordinated H(2)O by DMSO in [Li(H(2)O)(4)](+) follows an associative interchange mechanism. The suggested mechanisms are discussed in reference to available experimental and theoretical data.

Ligand Exchange Processes on Solvated Zinc Cations – DFT Analysis of Hydrogen Cyanide Exchange on [Zn(HCN)6]2+

“…Following the suggestions of Hartmann et al, [13] and for comparison with recent studies on solvent exchange at Li + , [17,18,22] Be 2+ , [19,23] and Al 3+ , [20,21] we fully optimized the structures at the B3LYP/6-311+G** level of theory [24] and characterized by computation of vibration frequencies the structures as local minima or transition states.…”

“…15 , M = Li (m = 4, n = 1), [22] Be (m = 4, n = 2), [23a] Zn (m = 6, n = 2) and Al (m = 6, n = 3) [21] complexes versus the charge on the metal ion. [21] shows that the sum of the metal-nitrogen bond lengths (∑(M-NCH)) as a quantum [21].…”

Computational Perspectives on Organolithiums

“…Larger aggregates are most frequently monosolvated or disolvated depending on the size of the solvent (and solute), but lithium is generally considered to be tetracoordinated [36,39]. Solvent exchange between the coordinating solvent and the solvent in the bulk and flexibility due to hemilabile ligands are also processes that may take place, and these are dynamical temperature-and concentration-dependent processes, phenomena well studied by both NMR and computational techniques [28,[48][49][50][51][52][53][54][55]. Solvation energies of lithium organic compounds are routinely estimated computationally and have been compared with experimental results in several studies.…”

Application of High Pressure in the Elucidation of Inorganic and Bioinorganic Reaction Mechanisms

“…The kinetics of the ligand exchange process between solvated lithium ions (solvated by g-butyrolactone, (S), an industrially pertinent solvent) and lithium ions complexed with the cryptands, C222 or C221, (L), have been studied by 7 Li NMR spectroscopy. 380 Analysis from earlier studies using other solvents indicated that the reaction follows two competing mechanisms, bimolecular association (between Li (L) þ and Li(S) þ ) and unimolecular reaction involving Li(L) þ . The former process would be expected to proceed by an associative mechanism and when S ¼ gbutyrolactone, the present study yields an entropy of activation of a value that supports an associative interchange mechanism, although the rate of this reaction exhibited almost no dependence upon pressure.…”

“…This study confirmed that experimental and theoretical evidence supports a coordination number of four for both DMSO and DMSO/water mixtures. 386 A computational study suggested that ligand exchange on [Li(DMSO) 4 ] þ follows a limiting associative (A) mechanism, whereas displacement of coordinated water by DMSO follows an associative interchange (I a ) mechanism. A similar investigation indicated that Li þ ions in acetonitrile exhibit four-coordination and that in a binary aqueous acetonitrile mixture, the more strongly coordinating water leads immediately to formation of [Li (H 2 O) 4 ] þ .…”