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

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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 HnLi(n= 3 or 4) and L ligands.

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