Template synthesis of 1-(8'-amino-α-naphthyl)-4-(8 '-amino-α-naphthylanline)- 1-azabuta-1,3-diene, a tetraaza half-cyclised ligand, and characterisation of its copper(II) complexes

Abstract

<span style="font-size:12.0pt;line-height: 115%;font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:hi"="" lang="EN-IN">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 sulphexide (DMSO). Its <i>pK</i>_a<i> </i>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 <span style="font-size:12.0pt; line-height:115%;font-family:" times="" new="" roman","serif";mso-fareast-font-family:="" hiddenhorzocr;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">glass <span style="font-size:12.0pt;line-height:115%; font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:hi"="" lang="EN-IN">at 77 K are almost identical and have rhombic features (<g<sub>3>, 2.40; <g<sub>2>, 2.08; <g<sub>1>, 2.01; <<i>A</i>₃>, 137×10^-4 cm^-1; <<i>A</i>₂>, 18×10^-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 <span style="font-size:12.0pt;line-height:115%;font-family:" times="" new="" roman","serif";="" mso-fareast-font-family:hiddenhorzocr;mso-ansi-language:en-in;mso-fareast-language:="" en-in;mso-bidi-language:hi"="" lang="EN-IN">quasi<span style="font-size:12.0pt; line-height:115%;font-family:" times="" new="" roman","serif";mso-fareast-font-family:="" "times="" roman";mso-ansi-language:en-in;mso-fareast-language:en-in;="" mso-bidi-language:hi"="" lang="EN-IN">reversible two-electron ligand oxidation with an E_1/2 of 0.12V vs saturated calomel electrode (SCE) and a irreversible metal oxidation process at a low potential (< 0.5 V vs SCE).</span></span></g<sub></g<sub></g<sub></span></span></span>