Specific coordination phenomena of alkaline earth metal ions with aromatic sulfonate ions in alcohols and binary solvents of acetonitrile-alcohols

摘要

The specific interactions between alkaline earth metal (Mg~(2+), Ca~(2+), or Ba~(2+)) and p-toluenesulfonate (L~-), 1,5-naphthalenedisulfonate (L~(2-)), or 1,3,6-naphthalenetrisulfonate (L~(3-)) ions (from the tetraethylammonium salt of L~-, L~(2-), or L~(3-)) have been examined bymeans ofUV-visible spectroscopy in primary alcohols (frommethanol to hexanol) as well as in the binary acetonitrile-alcohols (MeCN-MeOH, MeCN-EtOH), ethanol-methanol (EtOH-MeOH) and methanol-water (MeOH-H_2O) solvents. The precipitation of non-charged species (e.g. ML~0) and the successive re-dissolution of the precipitates, with increasing concentration of M(ClO_4)_2, have revealed the formation of cationic charged species or "reverse coordinated" species, M_2L~(2+), even in the protic media aswell as in the aprotic solvent MeCN. The solubility products (Ksp) and the "reverse coordination" constants (2M~(2+)+L~(2-) ?M_2L~(2+), K_(2(-2))=[M_2L~(2+)] / [M~(2+)]2 [L~(2-)]) have been evaluated. In ethanol, both phenomena of the precipitation of ML~0 and the successive re-dissolution to produceM_2L~(2+) are observed for Ca~(2+) or Ba~(2+), but not forMg~(2+). In butanol, the interaction between Mg~(2+) and the L~(2-) causes the complete precipitation of MgL~0 (pK_(sp)=10.39) and also the successive re-dissolution of Mg_2L~(2+) (log K_(2(-2))=8.08). Even inmethanol, the interaction between Ba~(2+) and L~(2-) results in precipitation (log K_(sp)=8.28) and the "reverse coordinated" species, Ba_2L~(2+) (log K_(2(-2))=5.58). The interaction of Ba~(2+) with L~- or L~(3-) causes no precipitation inmethanol; however, in all the other alcohols, it results both in precipitation (BaL2 or Ba3L2) and the "reverse coordinated" species, BaL~+ or Ba_2L~+. The formulation for the formation constants (K2(-3)) for M~(2+) and L~(3-) is newly presented and the constants (2Ba~(2+) + L~(3-) ? Ba_2L~+, K2(-3)=[Ba_2L~+] / [Ba~(2+)]~2 [L~(3-)]) are evaluated in ethanol and propanol as well as in the binary EtOH-MeOH solvents, up to 70% (v/v) MeOH. The donicities toward M~(2+) of the media have been related to the pK_(sp) and "reverse coordination" constants for L~-, L~(2-) and L~(3-).