Copper(II) bipyridyl and iminopyridyl analogoues of streptonigrin

Abstract

The crystal structures of (3-amino-6,6′-dimethyl-2,2′-bipyridine) dichlorocopper(II)[CuL¹Cl₂], and aqua[3-imido-6-(methoxycarbonyl)-2,2′-bipyridine-6′-carboxylato]copper(II), [CuL³(H₂O)], have been determined. The complex [CuL¹Cl₂] crystallizes in space group Pnama with a= 19.434(3), b= 7.427(2), c= 9.403(1)Å and Z= 4. The structure has been refined to a final R value of 0.057 based on 680 independent reflections. The copper(II) centre exhibits tetrahedral co-ordination to the bipyridyl nitrogens of L¹ and two chlorine atoms. Crystals of [CuL³(H₂O)] were grown from a solution of 3-amino-6,6′-bis(methoxycarbonyl)-2,2′-bipyridine (L²) and excess Cu^II. The complex crystallizes in space group P2₁/n with a= 3.724(2), b= 14.375(3), c= 22.953(5)Å, β= 90.72(3)° and Z= 4. The structure has been refined to a final R value of 0.061 based on 944 independent reflections. The Cu^II centre is square planar with a slight tetrahedral deformation, and co-ordinates to an imino nitrogen, adjacent pyridyl nitrogen, carboxylate oxygen and a water molecule. The implications of these results on the types of complexes formed by streptonigrin are discussed.