Study of ion–solvent interactions of some tetraalkylammonium halides in THF + CCl4 mixtures by conductance measurements

Conductivities of some tetraalkylammonium halides, viz. tetrapentylammonium chloride (Pen4NCl), tetrahexylammonium chloride (Hex4NCl), tetraheptylammonium chloride (Hep4NCl), and tetraoctylammonium chloride (Oct4NCl) were measured at 298.15 K in THF + CCl4 mixtures with 40, 60 and 80 mass% of THF. A minimum in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed at concentrations which is dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M+ + X− ↔ MX, KP) and triple-ions (2M+ + X− ↔ M2X+; M+ + 2X− ↔ MX2−, KT). A linear relationship between the triple-ion formation constants [log(KT/KP)] and the salt concentrations at the minimum conductivity (log Cmin) was given for all salts in THF + CCl4 mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R4N+⋯X−).