A Ternary Complex of Vanadium(V) with 4-(2-Pyridilazo)-resorcinol and Thiazolyl Blue and its Application

^aDepartment of General and Inorganic Chemistry, Plovdiv University, 24 Tsar Assen Str., 4000 Plovdiv, Bulgaria,  kgavazov@abv.bg
^bDepartment of Chemical Technology, Plovdiv University, 24 Tsar Assen Str., 4000 Plovdiv, Bulgaria.

Absrtract
A new ternary complex of vanadium(V) with 4-(2-pyridilazo)-resorcinol (PAR) and thiazolyl blue (MTT) has been obtained and studied by using an extraction-spectrophotometric method. The complex absorbs light at 560 nm with a molar absorptivity coefficient of 3.84x10⁴ L mol^-1 cm^-1 at the optimum extraction conditions: pH=5.8±0.7, C_PAR=1.2x10^-4 mol L^-1, C_MTT=1.0x10^-4 mol L^-1, extraction time - 2 min. Beer’s law is obeyed up to 1.5 mg V(V) mL^-1. The following constants have been calculated: the distribution constant (Log K_D=1.61), the association constant (Log b=15.9), the extraction constant (LogK_ex=17.5) and the recovery factor (R=97.49%). The composition of the complex has been found to be V(V):PAR:MTT=1:2:3. The effect of foreign ions has been studied and a sensitive, selective and precise extraction-spectrophotometric method for the direct determination of vanadium(V) and indirect determination of vanadium(IV) has been proposed.

Keywords: vanadium, speciation, 4-(2-pyridilazo)-resorcinol, tetrazolium salt, extraction, spectrophotometry, catalysts