Reaction of 1,1,3,3-tetramethoxypropane with 1,8-diaminonaphthalene in presence of a nickel(II) template in aqueous medium generates the free acyclic ligand 1-(8'-amino-α-naphthyl)-4-(8'-amino-α-naphthylamine)-1-azabuta-1,3-diene (LH; H: dissociable proton) as a 1.5 hydrate. The ligand undergoes acid dissociation in non-aqueous solvents which is reflected in its 13C NMR spectrum in deuteriated dimethyl sulphoxide (DMSO). Its pK(a) value determined in DMSO from conductivity data is 5.18. With copper(II) perchlorate, LH forms air sensitive complexes of type CuL(ClO4).3H2O and CuL(ClO4).DMF (DMF: dimethylformamide). In both the complexes, the perchlorate anion is weakly bound to the metal as revealed by their conductivity in DMF suggesting a CuN4O2+ chromophore. Their EPR spectra in DMF-toluene glass at 77 K are almost identical and have rhombic features (<g3>, 2.40; <g2>, 2.08; <g1>, 2.01; <A3>, 137x10-4 cm-1; <A2>, 18x10-4 cm-1) indicating that the coordination sphere around the copper ion is of distorted square-pyramidal type. ZINDO calculations show that the CuL+ fragment has a butterfly like shape with the naphthalene fragments spanning like two wings and the metal in the N4 plane. In cyclic voltammetric experiments in DMF at a platinum electrode, the complexes show a quasi-reversible two-electron ligand oxidation with an E(1/2) of 0.12 V vs saturated calomel electrode (SCE) and an irreversible metal oxidation process at a low potential (< 0.5 V vs SCE).
|Original language||English (US)|
|Number of pages||7|
|Journal||Indian Journal of Chemistry - Section A Inorganic, Physical, Theoretical and Analytical Chemistry|
|State||Published - Jan 1 2000|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry