Coordination phenomena of alkali metal, alkaline earth metal, and indium ions with the 1,3,6-naphthalenetrisulfonate ion in protic and aprotic solvents

Abstract

Not only in acetonitrile (MeCN) but also in primary alcohols (from methanol to 1-hexanol), the coordination ability of alkali metal (Li+, Na+), alkaline earth metal (Mg2+, Ca2+, or Ba2+), and indium (In3+) ions with the 1,3,6-naphthalenetrisulfonate ion (L3−, 1.0×10−4moldm−3) has been examined by means of UV–visible spectroscopy. In MeCN, the precipitation takes place completely between alkali metal or alkaline earth metal ions and L3−. In the presence of excess amounts of the metal ions, the precipitates of Li3L and Mg2L3 tend to re-dissolve partially to form the “reverse” coordinated species of Li4L+ and Mg2L+. However, those precipitates of Na3L, Ca3L2, and Ba3L2 would not re-dissolve even in the presence of large excess amounts of the metal ions in MeCN. Between In3+ and L3−, both precipitation and successive re-dissolution reactions can occur in all the primary alcohols. The solubility products (pKsp) and “reverse” coordination constants with L3− (log K4(1+), log K2(2+), and log K2(3+) for alkali metal, alkaline earth metal, and indium ions, respectively) have been evaluated in MeCN, the primary alcohols, and binary solvents of MeCN–H2O and MeCN–MeOH. Where, for instance, K4(1+)=[M4L+]/([M+]4 [L3−]) for the reaction: 4M++L3− ⇄ M4L+. DFT calculations have been performed to predict the coordinating structures of the Li4L+ species in MeCN.