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 tetraethylammnonium salt of L
−, L
2−, or L
3−) have been examined by means of UV-visible spectroscopy in primary alcohols (from methanol to hexanol) as well as in 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 protic media as well as the aprotic solvent MeCN. The solubility products (
Ksp) and the "reverse coordination" constants (2M
2+ + L
2− ↔ M
2L
2+,
K2(−2) = [M
2L
2+]/[M
2+]
2 [L
2−]) have been evaluated. In ethanol, both phenomena concerning the precipitation of ML
0 and the successive re-dissolution to produce M
2L
2+ are observed for Ca
2+ or Ba
2+, but not for Mg
2+. In butanol, the interaction between Mg
2+ and the L
2− causes the complete precipitation of MgL
0 (p
Ksp = 10.39) as well as the successive re-dissolution of Mg
2L
2+ (log
K2(−2) = 8.08). Even in methanol, the interaction between Ba
2+ and L
2− results the precipitation (p
Ksp = 8.28) and the "reverse coordinated" species, Ba
2L
2+ (log
K2(−2) = 5.58). The interaction of Ba
2+ with L
− or L
3− causes no precipitation in methanol, however, in all the other alcohols, it results in both precipitation (BaL
2 or Ba
3L
2) and "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 the binary EtOH-MeOH solvents, up to 70% (v/v) MeOH. The donicities towards M
2+ of the media have been related to the p
Ksp and "reverse coordination" constants for L
−, L
2−, and L
3−.
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