• M C Saxena

      Articles written in Journal of Chemical Sciences

    • Inter-ligand stacking interactions in some0-phenanthroline amino acid biligand complexes

      Shikha Bajpai M C Saxena

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      Biligand complexes of the type metal/o-phenanthroline/amino acid, where metal = Co2+, Ni2+, Cu2+, Zn2+, Cd2+; and amino acid = β-phenyl alanine or tryptophan have been found to show inter-ligand stacking interactions in aqueous solutions. This interaction has been evaluated quantitatively from a knowledge of the formation constants of these complexes (and that of the identical biligand complex with α-alanine) as determined by potentiometric pH titration at25°C and an ionic strength,I=0·2 (mol dm−3, KNO3) by following the Irving-Rossotti approach. The sequence of interaction is tryptophan > β-phenyl alanine.

    • 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.

    • 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.

    • Electronic spectral studies on rare earth doped pseudogarnets

      Rashmi Singhai Sudhir N Limaye M C Saxena

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      Spectral parameters viz. oscillator strengths (P), Judd-Ofelt parameters (τλ), inter-electronic repulsion (Racah)∂Ek parameters (IERP) and nephelauxetic ratio (δE3/δE1) have been determined using aqueous solutions of representative lanthanide (rare earth) (III) ions, Pr(III), Nd(III), Sm(III), Eu(III), and Er(III) and rare earth-doped concentrated (∼ 1.0 M) solutions of pseudogarnets sodiumm-silicate, sodium molybdate and sodiumm-vanadate. These parameters have been studied as a function of (i) symmetry around the Ln(III) ions, and (ii) matrix environment due to different pseudogarnets.

      The electronic transitions for various Ln(III) ions and changes in their positions due to corresponding changes in matrix environment are observed to show red shift. The oscillator strength values increase significantly in the sequence aqua <MoO42−<VO3<SiO32−. The τλ values are found to lie in the orderτ6>τ4>τ2. The∂Ek and∂E3/∂E1 values are observed to lie in the theoretically calculated ranges. The nature of dopant-matrix interaction appears to change from ionic to ionocovalent on going across the Ln(III) series.

    • Ground termL andJ quantum number profiles of the oscillator strengths (fJO) andpH values of some lanthanoids in aminopolycarboxylate ligand environments

      Puspanjali Rout Rashmi Singhai Sudhir N Limaye M C Saxena

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      Electronic spectral studies of some lanthanoids [(viz. Pr(III), Nd(III), Sm(III), Eu(III), Dy(III), Er(III) and Tm(III)] in aminopolycarboxylate (viz. IMDA, NTA, HEDTA, EDTA, CDTA and DTPA) environment have been undertaken with a view to evaluate the oscillator strengths (fJO), Judd-Ofelt parameters (τλ), inter-electronic repulsion Racah parameters (∂Ek) and nephelauxetic ratios (∂E3/∂E1). The parameters have been evaluated for the entirepH range (pH 2–9) with intervals of 0.5 in order to study the dependence of oscillator strengths onpH values. The extent of covalency (via parameterτ2) and symmetry (via parametersτ4 andτ6) in the metal-ligand interaction have been estimated with the help of τλ parameters. The values of oscillator strengths and Judd-Ofelt parameters have been discussed in the light of coordination number of lanthanoid metal ions, denticity and basicity of the ligands. The metal-ligand bonding pattern has been studied in the light of changes in Racah parameters and the nephelauxetic ratio. The oscillator strength values for some specific hypersensitive transitions and for the transition whereUλ values are significantly large have been studied as a function of ground termL andJ quantum numbers of the lanthanoids.

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