Physico-chemical studies on the chelation behaviour of acenaphthenequinone monothiosemicarbazone (AQTS) with some bivalent metal ions
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The stability constants of the chelates formed from acenaphthenequinone monothiosemicarbazone and magnesium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) or cadmium(II) have been determined pH-metrically in 75% v/v aqueous dioxan at various ionic strengths of NaClO4 and at different temperatures. The method of Bjerrum and Calvin(1, 2) as modified by Irving and Rossotti(3), has been used to determine the ñ and pL values. The stability constants were calculated on an IBM 360 FORTRAN-IV computer patterned after that of Sullivanet al.(4) to give βn values using a weighted least squares method. The Smin, values were also calculated. The thermodynamic stability constant has been determined by extrapolating the log K1vs √μ plot at zero ionic strength. The other thermodynamic functions have been calculated from the stability constants obtained for different temperatures at constant ionic strength. The bivalent metal stability sequence of AQTS chelates is in agreement with reported metal orders for other chelating reagents. The order of free energies and enthalpies of chelate formation for AQTS are: Mn2+<Co2+<Ni2+<Cu2+>Zn2+.
KeywordsCadmium Ionic Strength Dioxan Stability Constant NaClO4
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