Etude vibrationnelle des associations ioniques dans les solvants aprotiques. 7. Solvatation de (LiNCS)_p par les solvants peu polaires

Abstract

Solutions of LiSCN in donor solvent – benzene mixtures have been investigated by solubility measurements and by infrared spectrometry. The state of aggregation of LiSCN has been obtained from the ir spectra in the ν(CN) region 2100–2000 cm−1. The selected solvents (tetrahydrofuran, pyridine, acetone, diethylcarbonate, butylacetate, ethylmethylketone) are more or less associating towards LiSCN. The addition of benzene causes an increase of the associating ability of the solvents. By changing the donor solvent and the amount of benzene it has been possible to obtain the ion pair LiNCS, the dimer (LiNCS)2, and higher aggregates in various proportions. The solvation number of lithium has been measured in solvent vibration regions. Each step of aggregation is accompanied by lithium desolvation. The coordination of lithium in all the species which are formed remains equal to 4, or slightly lower in some cases.

A Computational Study of Lithium Enolate Mixed Aggregates

“…50 Similarly, infrared spectra of lithium thiocyanate in benzene-THF mixtures indicate that each lithium has 2-3 THF's in the monomer and two in the dimer. 51 The CIP portion of diphenyl-n-hexyllithium in benzene with THF is of the form RLi‚2THF. 52 Titrating with HMPA, a strongly coordinating reagent for lithium cation, is another useful technique.…”

“…Studies of equilibria with THF in toluene suggest that the dimer of lithiated cyclohexanone phenylimine is disolvated and the monomer is trisolvated . Similarly, infrared spectra of lithium thiocyanate in benzene−THF mixtures indicate that each lithium has 2−3 THF's in the monomer and two in the dimer . The CIP portion of diphenyl- n -hexyllithium in benzene with THF is of the form RLi·2THF .…”

Unusual behavior of the conductivity of LiNO3 in tert-butanol: ion clustering or ion-pair aggregation

“…In aprotic solvents such as tetrahydrofuran, diethyl ether, pyridine, and diethyl carbonate, the salts LiNCS and LiBr form ion pairs that can agglomerate (8,9). For example, the following species have been detected by various spectroscopic methods (8,9): The trimer (LiNCS)3,s was not detected.…”

“…For example, the following species have been detected by various spectroscopic methods (8,9): The trimer (LiNCS)3,s was not detected. The tetramer has a cubane-like structure.…”