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Subject: Chemistry × Author: Jain, Sweety × End date: 2009 × Start date: 2002 × Type: Thesis ×
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    ThesisItemOpen Access
    Stability constants of mixed ligand complexes of some bivalent transition metal ions under laboratory and soils conditions
    (CCSHAU, 2005) Jain, Sweety; Nepal, J.K.
    The stability constants of binary and ternary complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) with N-(2-hydroxyethyl) imino diacetic acid, iminodiacetic acid, nitrilotriacetic acid, lactic acid, glycolic acid, thioglycolic acid were determined potentiometrically at ionic strengths ( = 0.1 and 0.2 M KNO3) and temperature 298±0.5K. The protonation constants of the ligands were determined using Calvin-Bijerrum pH. titration technique as modified by Irving and Rossotti at ionic strengths ( = 0.1 and 0.2 M KNO3) and temperature (298±0.5 K). The following computational techniques were used. i) Interpolation of half values ii) Pointwise calculation method iii) Correction term method The calculation of stability constants for binary (1:1) systems and ternary (1:1:1) systems were carried out by Ramamoorthy and Santapa method. The stability constants for binary systems Mn(II) / Fe(II) / Co(II) / Ni(II) / Cu(II) / Zn (II) – HIMDA / IMDA / NTA / Lactic Acid / Glycolic acid / Thioglycolic acid were evaluated to characterize the stability Introduction of ternary complexes. The stability constants in these systems were found to follow the general trend. Mn(II) < Fe(II) > Co(II) < Ni (II) < Cu (II) > Zn (II). Lactic acid complexes were found to be more stable than other complexes with these metal ions. The stability constants of ternary systems [M(II) – HIMDA / IMDA / NTA – Lactic acid / Glycolic acid / Thioglycolic acid] in terms of metal ions follow the general trend Mn(II) < Fe(II) > Co(II) < Ni(II) < Cu(II) > Zn(II). The ternary complexes with lactic acid as secondary ligand are more stable as compared to others. The stability constants in all systems generally decrease with increase in ionic strength. The variation in stability due to ligand – ligand interaction was interpreted by the expression.  log KM, which quantities the stability of ternary complexes relative to binary parent complex. In present investigation the variation in hetero-ligand interaction follow the trend as given below : At  = 0.1 M KNO3, temperature (298±0.5 K) Mn(II) – IMDA-Lactic acid > HIMDA-Lactic acid > NTA – Lactic acid. Fe(II) – IMDA-Lactic acid > HIMDA-Lactic acid > NTA – Lactic acid. Co(II) – HIMDA -Lactic acid > IMDA -Lactic acid > NTA – Lactic acid. Ni(II) – IMDA-Lactic acid > HIMDA-Lactic acid > NTA – Lactic acid. Cu(II) – IMDA-Lactic acid > HIMDA-Lactic acid > NTA – Lactic acid. Zn(II) – IMDA-Lactic acid > HIMDA-Lactic acid > NTA – Lactic acid. Activity trend of complexes against C. falcatum and F. oxysporum : In case of F. oxysporum the decreasing order of anti-fungal activity of complexes of system at  = 0.1 M KNO3 (298±0.5K) is as follows : Zn(II)-NTA-Thioglycolic acid > Zn(II)- NTA-Glycolic acid > Zn (II)-NTA > Zn(II) And in case of C. falcatum the decreasing order of antifungal activity (MIC) is : Zn(II)-NTA-Glycolic acid > Zn(II)-NTA-Thioglycolic acid / Zn(II)-NTA > Zn(II). Effect of chalating agent on DTPA extractable metals : Extractability of metals increases with the addition of NTA. But when lactic acid was added with NTA extractability of Zn, Co, Cu decreased while Ni, Mn increased but of Zn remained same.