BIS(DIDENTATE) OPEN-CHAIN AND TETRADENTATE PSEUDO-MACROCYCLIC BRIDGING COORDINATION MODES OF NITROSO-2,4-DIOXOPYRIMIDIN-6-YL)BUTANE-1,4-DIAMINE

The reaction of nitroso-2,4-dioxopyrimidin-6-yl)butane-1,4-diamine (H2 L2) with copper(II) salts in ethanol yielded mononuclear complexes of formula [Cu(HL2)X] (X is the anion of the corresponding copper salt). These mononuclear precursors reacted with either Cu-II and 2,2'-bipyri dine (bipy) or [NiL][ClO4](2) (L = 2,14-hexamethyl-1,4,8,11-tetraazacy clotetradecane) to afford the homodinuclear complexes [Cu(mu-Cl)(mu-L- 2)Cu(bipy)]ClO4 . 2H(2)O1 and [LNi(mu-H2L2)NiL][ClO4](4) 2, respective ly. Within the dinuclear cation of 1 the copper(II) ions exhibit a 4 1 co-ordination environment, The dioxime ligand bridges the basal pla nes of the metal ions through the oximate groups in a symmetrical syn- syn fashion, Cu(1) Cu(2) being 3.364(3) Angstrom, whereas their apical positions are occupied by a bridging CI anion, with a Cu(1)-Cl(1)-Cu( 2) angle of 80.42(7)degrees. A magnetic study of 1 revealed that the a ntiferromagnetic exchange is so strong as to cause complete spin pairi ng at room temperature. Complex 2 consists of a homodinuclear [LNi(mu- H2L2)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) Angstrom. The nickel(II) ions are octahed rally 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 H2L2 are compared to those of them related itroso-2,4-dioxopyrimidin-6-yl)propane-1,3-diamine (H 2L1).