A Study and Optimization of Complexation of Cobalt Ions with Dihydroquercetin in Aqueous Solutions

This work continues a series of studies devoted to complex formation of ions of biogenic metals with the flavonoid dihydroquercetin (DHQ). The interaction of Со 2+ ions with DHQ in aqueous solutions has been investigated. It has been found that, at different pH of a solution, complex compounds (CC) with different stoichiometry are formed; a variation of the pH value of a solution from 6.0 to 7.0 results in the formation of compounds ( 1 )–( 3 ) with the metal : flavonoid ligand ratio (Met : L) from 1 : 2 at рН 6.0 ( 1 ), through 2 : 3 at pH 6.4–6.7 ( 2 ), to 1 : 1 at рН 6.8–7.0 ( 3 ). By using the thermogravimetric method and the data of the elemental analysis, the most probable composition of the compounds with the determination of the amount of bound water has been proposed: [CoL 2 (H 2 O) 4 ] for ( 1 ), [Co 2 L 3 (ОН)(H 2 O) 4 ] for ( 2 ), and [CoL(ОН)(H 2 O) 2 ] for ( 3 ). Conditions for the optimization of product yield in the complexation reaction of Со 2+ ions with DHQ in an aqueous solution have been determined for compound ( 2 ): the рН value of solution 6.7; the reaction time 15 min; the temperature of the reaction solution 90°С; the molar ratio of the initial reagents DHQ : Со 2+ 1 : 1.5; the initial concentration of DHQ 0.020 mol/L and that of Со 2+ 0.030 mol/L; and the use of CoSO 4 ⋅ 7H 2 O as a source of cobalt ions. The yield of the product is 81.8%.