A method of obtaining a complex acidic salt of a divalent metal and a dicarboxylic acid includes heating water in a reactor; adding a dicarboxylic acid to the heated water; stirring the water to dissolve the dicarboxylic acid in the heated water to produce a solution or a suspension of the dicarboxylic acid in the heated water; adding MeO to the solution or the suspension, where Me is a divalent metal; continuing the stirring of the solution or suspension until formation of the complex acidic salt Me(AcH)2.nH2O begins, where Ac is an anion of the dicarboxylic acid, and n=0-8; cooling the complex acidic salt to below a temperature of crystallization; sedimenting the complex acidic salt; filtering the complex acidic salt to remove water from the complex acidic salt; and drying the complex acidic salt.