• Sangeeta Verma

      Articles written in Journal of Chemical Sciences

    • Tetrad effects in mixed ligand lanthanide chelates. Part I: Lanthanide, EDTA/NTA, IMDA ternary systems

      Sangeeta Verma M C Saxena

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      The occurrence of tetrad effects has been studied for the variations in formation constants (logKMALMA) of the mixed ligand complexes of the type [Ln(III).A.L.] (where Ln(III)=La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III) or Dy(III); A=EDTA or NTA; L=IMDA), with the number of 4f electrons of the tervalent lanthanides. A differential plot method has been suggested for locating the (minor) breaks at the 4f3–4f4 and 4f10–4f11 stages in the Ln(III) series.

    • Tetrad effect in mixed-ligand lanthanide chelates. Part II: Lanthanide. CDTA/DTPA. orcinol/resorcinol/phloroglucinol ternary systems

      Sangeeta Verma M C Saxena

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      The variation profiles of certain properties of the lanthanide [Ln(III)] series show discontinuities at or around Gd(III) (4f7 stage), Nd (IH)-Pm(III) (4f3−4f4 stage) and Ho (III)-Er (III) (4f10−4f11 stage) due to the presence of a tetrad effect. In the present work the occurrence of the tetradic phenomenon has been studied for the formation constants, log KMALMA of the mixed-ligand Ln (III) chelates of the type [Ln(III).A.L], where Ln(III) = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb (III) or Dy(III); A = CDTA or DTPA; L = orcinol, resorcinol or phloroglucinol. The presence of the tetrad effect in log KMALMA values has been tested with the help of the straight line approximation method, differential plot method and inclined-W hypothesis. The magnitude of the effect has been found to lie in the sequence f7 > f3 −f4.

    • Periodicity in the formation constant values of lanthanide(III). aminopolycarboxylate. resorcinol/orcinol/phloroglucinol mixed ligand complexes

      Sangeeta Verma S N Limaye M C Saxena

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      Formation constants (logKMALMA) of mixed ligand complexes[Ln(III).A.L.], where Ln(III) = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+ or Dy3+; A=NTA, HEDTA or EDTA and L = resorcinol (res), orcinol (orc) or phloroglucinol (phl) have been determined pH-metrically using the Irving-Rossotti approach at 25°C and at an ionic strength,I = 0·2(mole dm−3, NaClO4). The logKMALMA values lie in the sequence: (i) NTA > HEDTA > EDTA and (ii) orc > res > phl with respect to primary (A) and secondary (L) ligands, respectively.

      Periodicity has been observed in the formation constant values, which lie in the sequence La3+ < Ce3+ < Pr3+ < Nd3+ < Sm3+ < Eu3+ > Gd3+ < Tb3+ < Dy3+ with respect to Ln(III) ions. The evaluated extrastabilization and nephelauxetic ratio values lend support to inter-electronic repulsion theory; these values and the magnitude of the tetrad effect lie in the sequencef7>f3f4f10f11. Hydration numbers (HN) of Ln(III) ions have been calculated; tetrad effect is present in HN.

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