Bis(didentate) open-chain and tetradentate pseudo-macrocyclic bridging co-ordination modes of N,N′ -bis(1,3-dimethyl-5-nitroso-2,4-dioxopyrimidin-6-yl)butane-1,4-diamine

Abstract

The reaction of N,N′ -bis(1,3-dimethyl-5-nitroso-2,4-dioxopyrimidin-6-yl)butane-1,4-diamine (H ₂ L ² ) with copper(II) salts in ethanol yielded mononuclear complexes of formula [Cu(HL ² )X] (X is the anion of the corresponding copper salt). These mononuclear precursors reacted with either Cu ^II and 2,2′-bipyridine (bipy) or [NiL][ClO ₄ ] ₂ (L = d,l -5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) to afford the homodinuclear complexes [Cu(µ-Cl)(µ-L ² )Cu(bipy)]ClO ₄ ·2H ₂ O 1 and [LNi(µ-H ₂ L ² )NiL][ClO ₄ ] ₄ 2, respectively. Within the dinuclear cation of 1 the copper(II) ions exhibit a 4 + 1 co-ordination environment. The dioxime ligand bridges the basal planes of the metal ions through the oximate groups in a symmetrical syn-syn fashion, Cu(1) · · · Cu(2) being 3.364(3) Å, whereas their apical positions are occupied by a bridging Cl anion, with a Cu(1)–Cl(1)–Cu(2) angle of 80.42(7)°. A magnetic study of 1 revealed that the antiferromagnetic exchange is so strong as to cause complete spin pairing at room temperature. Complex 2 consists of a homodinuclear [LNi(µ-H ₂ L ² )NiL] ⁴⁺ cation and four non-co-ordinated perchlorate anions. The ligand adopts an unusual bis(didentate) open-chain co-ordination mode by elimination of the Cu atom occupying the inner site of the pseudo-macrocyclic ligand in the mononuclear precursor. This results in a Ni · · · Ni distance of 13.370(3) Å. The nickel(II) ions are octahedrally co-ordinated by four nitrogen atoms belonging to the macrocyclic ligand L and the N and O atoms from the nitroso and the neighbouring exocyclic group. The co-ordination modes of H ₂ L ² are compared to those of the related N,N′ -bis(1,3-dimethyl-5-nitroso-2,4-dioxopyrimidin-6-yl)propane-1,3-diamine (H ₂ L ¹ ).