Studies on some eight-coordinated lanthanide(III) metal complexes of a pentadentate schiff base

Abstract

Trivalent rare earth metal complexes of 2,6-diacetlpyridyl bis(pyrazinecarboxylic hydrazone), dappyzh, of composition [Ln(dappyz )CI₃].3H₂O (where Ln=La, Pr, Nd, Sm, Eu Gd, Tb, Dy and Y) have been synthesized and their structures studied by elemental analyses, electrical conductance, magnetic susceptibility, electronic, IR, ¹H, ¹³C and ¹³⁹La NMR spectral techniques. Various bonding parameters, viz., b, b^1/2,%d and ŋ calculated for Pr(Ill), d(III), Sm(IlI) and Dy(III) complexes suggest ionie nature of bonding between the metal and ligand. The hypersensitive band profile of Nd(IlI) complex implies coordination number to eight in the present complexes. Further, the oscillator strengths and three intensity parameters (Tλ =2,4,6), c )computed from Judd- Ofelt equation, have been found in good agreement with the experimental oscillator strength values. IR and NMR spectral studies suggest a neutral pentadentate nature of dappyzh, the bonding sites being carbonyl oxygens, azomethine nitrogens and pyridine ring nitrogen. Low site molecular symmetry has been proposed in the present complexes on the basis of the line width of the ¹³⁹La NMR signal.