Metal complexes of a new class of polydentate Mannich bases: Synthesis and spectroscopic characterisation

A new class of polydentate Mannich bases featuring an N2S2 donor system, bis((2-mercapto-N-phenylacetamido)methyl)phosphinic acid H3L1 and bis((2-mercapto-N-propylacetamido)methyl)phosphinic acid H3L2, has been synthesised from condensation of phosphinic acid and paraformaldehyde with 2-mercaptophenylacetamide W1 and 2-mercaptopropylacetamide W2, respectively. Monomeric complexes of these ligands, of general formula K2[CrIII(Ln)Cl2], K3[M′II(Ln)Cl2] and K[M(Ln)] (M′ = Mn(II) or Fe(II); M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The structures of new ligands, mode of bonding and overall geometry of the complexes were determined through IR, UV–Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) and Fe(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Co(II), Zn(II), Cd(II) and Hg(II) complexes. Complex formation studies via molar ratio in DMF solution were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1).

The reaction of bis((2-mercapto-N-phenylacetamido)methyl)phosphinic acid H3L1 and bis((2-mercapto-N-propylacetamido)methyl)phosphinic acid H3L2 with metal chloride salt in a 1:1 mol ratio in the presence of KOH as a base, affords an anionic four and six coordinate monomeric metal complexes. The study of complex formation via molar ratio has been investigated and results were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1).Figure optionsDownload as PowerPoint slide