Carbonyl compound dependent hydrolysis of mono-condensed Schiff bases: a trinuclear Schiff base complex and a mononuclear mixed-ligand ternary complex of copper (II)

Abstract

Two Schiff bases, HL¹ and HL² have been prepared by the condensation of N-methyl-1,3-propanediamine (mpn) with salicylaldehyde and 1-benzoylacetone (Hbn) respectively. HL¹ on reaction with Cu(ClO₄)₂•6H₂O in methanol produced a trinuclear Cu^II complex, [(CuL¹)₃(μ₃-OH)](ClO₄)₂•H₂O•0.5CH₂Cl₂ (1) but HL² underwent hydrolysis under similar reaction conditions to result in a ternary Cu^II complex, [Cu(bn)(mpn)ClO₄]. Both complexes have been characterised by single-crystal X-ray analyses, IR and UV–vis spectroscopy and electrochemical studies. The partial cubane core [Cu₃O₄] of 1 consists of a central μ₃-OH and three peripheral phenoxo bridges from the Schiff base. All three copper atoms of the trinuclear unit are five-coordinate with a distorted square–pyramidal geometry. The ternary complex 2 is mononuclear with the square–pyramidal Cu^II coordinated by a chelating bidentate diamine (mpn) and a benzoylacetonate (bn) moiety in the equatorial plane and one of the oxygen atoms of perchlorate in an axial position. The results show that the Schiff base (HL²) derived from 1-benzoylacetone is more prone to hydrolysis than that from salicylaldehyde (HL¹). Magnetic measurements of 1 have been performed in the 1.8–300 K temperature range. The experimental data clearly indicate antiferromagnetism in the complex. The best-fit parameters for complex 1 are g = 2.18(1) and J = −15.4(2) cm⁻¹.