Relationship between Triple Ion Formation Constants and the Salt Concentration of the Minimum in the Conductometric Curves in Low-Permittivity Solvents

Abstract

Conductivities of a number of uni-univalent salts, including tetrabutylammonium and lithium nitrophenolates, were measured at 25.0 °C in low-permittivity solvents such as tetrahydrofuran (THF, εr = 7.58), 1,2-dimethoxyethane (DME, 7.2), chloroform (4.8), and ethyl acetate (6.0). Minima in the conductometric curves (Λ−C 1/2) were observed for concentrations which were dependent upon both the salt and the solvent, C min = 1.73 × 10-4 mol dm-3 for 2,4-(NO2)2C10H5OLi (lithium 2,4-dinitro-1-naphtholate) in THF and 2.56 × 10-2 mol dm-3 for LiPic (lithium picrate) in DME. The observed molar conductivities including C min could be completely explained by the formation of ion pairs (M+ + X- ⇌ MX, K 1), “symmetrical” triple ions (2M+ + X- ⇌ M2X-, K 2; M+ + 2X- ⇌ MX2 -, K 3; K 2 = K 3), and (in some cases) additional formation of quadrupoles (2MX ⇌ M2X2, K 41). A linear relationship (the slope of −1) between the triple ion formation constants (log(K 2/K 1)) and the salt concentrations at the minimum (log C min) was given for all the salts in the various solvents, except for some systems in which a distinct formation of quadrupole takes place, e.g., LiNO3 in DME (K 1 = 3.16 × 1010, K 2 = 4.5 × 1013, and K 41 = 35). The formation of triple ions might be attributed to the ion sizes in solutions in which Coulombic interactions were the only main forces between ions (R4N+···X-). However, coordination (or covalent) bonding forces as well as Coulombic forces had to be considered for the lithium salts except for LiClO4 and LiBF4). Gutmann's donor and acceptor numbers of solvents (and not the permittivity) accounted for the larger difference of C min of lithium salts in THF and DME. In mixed solvents of THF and 2-ethyl-1-hexanol (εr = 7.58), the C min values of LiNO3 and 2,4-(NO2)2C10H5OLi increased with increasing contents of the hexanol, whereas the C min values of LiClO4 and Bu4NX (X- = NO3 -, 2,4-(NO2)2C10H5O-, and ClO4 -) remained constant for 0−30 vol % hexanol added to THF. The positive shifts in C min were explained quantitatively by the decrease in triple ion formation constants and/or by an increase in the quadrupole formation constants.

Anionic Palladium(0) and Palladium(II) Ate Complexes

“…Again, the addition of NBu 4 Br led to ab roadening and shift of the 19 Fs ignal, as one would expect for the formation of [L 3 PdBr] À ( Figure S46).…”

“…[19] Control experiments demonstrated that the addition of LiBr to as olution of Ld id not increase the conductivity ( Figure S34) and, thus,c onfirmed that the ligand does not interact with bromide anions to as ignificant extent. [19] Control experiments demonstrated that the addition of LiBr to as olution of Ld id not increase the conductivity ( Figure S34) and, thus,c onfirmed that the ligand does not interact with bromide anions to as ignificant extent.…”

Ion-pair and triple-ion formation of some tetraalkylammonium iodides in n-hexanol and its binary mixtures with o-toluidine

“…Solvent properties such as viscosity and the relative permittivity have been taken into consideration as these properties help in determining the extent of ion association and the solventsolvent interactions. Thus, extensive studies on electrical conductances in various mixed organic solvents have been performed in recent years [9][10][11][12][13] to examine the nature and magnitude of ion-ion and ion-solvent interactions. Tetraalkylammonium salts are frequently selected as desired electrolytes in conductance studies, even though they show little or no solvation in solution due to their low surface charge density [14,15].…”

Anionische Palladium(0)‐ und Palladium(II)‐At‐Komplexe

“…PdBr] À führte zum Verlust der Phosphanliganden [Gl (1). Wieaus der Literatur bekannt[19] wies reines LiBr in THF eine sehr geringe Leitfähigkeit auf.W eitere Kontrollexperimente zeigten, dass die Zugabe von LiBr zu einer Lçsung von Ld ie Leitfähigkeit nicht erhçhte (Abbildung S34), was eine signifikante Wechselwirkung des Liganden mit Bromidanionen ausschließt. Energieabhängige Fragmentierungsexperimente ergaben, dass die gemischten Komplexe die Liganden L Ph1 und L Ph2 leichter als La bspalteten (Abbildungen S25-S30), und bestätigten so dessen hçhere Affinitätzum anionischen Pd 0 -Zentrum.½L 3 PdBr À !½L 3Àn PdBr À þ n Lð1ÞDer Verlust des Phosphans,a ber nicht des Br À -Anions, verdeutlicht die Stärke der Wechselwirkung zwischen Metallzentrum und Halogenid.…”