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Picolinamidato complexes of copper(II)

The binding of metal ions by amides is of fundamental interest because of the importance of metal ions in biological systems. As a part of our ongoing research on preparation and characterization of metal complexes with small organic molecules of biological interest(1), we examined the structural properties of pyridine-2-carboxamidato complexes with copper(II). Picolinamide (pia), having the carboxamide group in o-position to endocyclic nitrogen, acts as chelating N, O-ligand in most of its complexes. There are only four complexes known so far where pia exhibits its N, N'-coordination mode. These are NiII, CuII, PdII and AuIII picolinamidato complexes. Square-planar coordination of metal ion is observed in all of them regardless of the number of the pia ligands present in coordination sphere. The violet copper complex 1 is a solvatomorph of already characterized one, [Cu(pia– H)2] 4H2O(2). The complex 1 crystallizes with two H2O molecules and additional difference is observed in shortening of Cu— Npy bonds in (1). The blue copper complex 2 is the first structurally characterized one with two pia ligands building up the coordination sphere and each exhibiting different coordination mode. One pia is bound to CuII ion in its usual N, O-chelating mode, while the other picolinamide ligand after deprotonation of the amide N atom achieves N, N'-coordination and thus forming dimeric [Cu2(ClO4)2( -pia– H)2(pia)2] units. None of commonly found supramolecular synthons in the amide structures denoted in terms of their graph set descriptors R22(8) for the dimers and C(4) for the chain arrangements are found in (1). In (2) robust R22(8) head-to-head dimers are formed between amidato groups of two neighboring molecules.

copper(II) complexes; picolinamide; H-bonding

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