Magnetic properties of mono-, bi-, and tri-nuclear copper(II) complexes of novel oxamato and oxamido ligands. Crystal structure of a mononuclear precursor

Abstract

Three novel ligands (H₃Lⁱ with i= 1,2, or 3) of the oxamato and oxamido types have been obtained and used to prepare the related ‘mononuclear’ entities [CuLⁱ]^–, H₃L¹ being N-(4-methyl-6-oxo-3-azahept-4-enyl)oxamic acid, H₃L² being N-(4-methyl-6-oxo-3-azahept-4-enyl)oxamide, and H₃L³ being N-methyl-N′-(4-methyl-6-oxo-3-azahept-4-enyl)oxamide. The complex of H₃L¹ crystallizes in the monoclinic system, space group P2₁/n, with a= 21.705(2), b= 9.380(1), c= 19.131(2)Å, and β= 101.17(1)°. The structure consists of three mononuclear anions [CuL¹]^–together with three sodium cactions and four water molecules. From the mononuclear fragments, binuclear complexes[CuLⁱCuL]⁺(L = 2,2′-bipyridine or diethylenetriamine) have been synthesized and spectroscopically characterized. A symmetrical binuclear complex [Cu₂L⁴][H₄L⁴=N,N′-bis-(4-methyl-6-oxo-3-azahept-4-enyl)oxamide] and two trinuclear complexes, [(CuL¹)₂Cu] and [(CuL¹)₂Zn], have also been prepared. The magnetic properties of these complexes have been investigated in the range 5–290 K. The importance of the antiferromagnetic interactions mediated by the oxamato and oxamido bridges is discussed with respect to the nature of the H_nLⁱ(n= 3 or 4) and L ligands.