A MIXED-BRIDGED CU-3 CLUSTER WITH AN ISOSCELES-TRIANGULAR ARRAY OF COPPER(II) IONS - SYNTHESIS, CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES

The reaction of H(2)L [H(2)L = N,N'-bis(1,3-dimethyl-5-nitrosopyrimidi ne-2,4 (1H,3H)-dion-6-yl)propyl-enediamine] with an excess of Cu(ClO4) (2).6H(2)O in ethanol gave the dinuclear complex [Cu(mu-HL)-Cu(H2O)(2) (EtOH)][ClO4](3) 1, magnetic studies of which revealed that the antife rromagnetic exchange interaction mediated by the oximate groups is so strong that it causes a complete spin coupling at room temperature. Th is compound reacted with NaCl in ethanol-water (5:1) to afford the mix ed-bridged trinuclear copper(II) complex [{Cu(mu-HL)Cu(H2O)CU(mu-Cl)][ ClO4](2).4.88H(2)O 2 the crystal structure of which was solved by sing le-crystal X-ray diffraction. Compound 2 consists of discrete trinucle ar cations [{Cu(mu-HL)Cu(H2O)Cu(mu-L)}(mu-Cl)](2+), non-co-ordinated p erchlorate anions and lattice water molecules. Within the trinuclear c ation, which has C-2, symmetry the three copper ions are arranged at t he corners of an isosceles triangle. Each terminal copper atom Cu(2).. .Cu(2) distance of 3.373(4) Angstrom, whereas a chloride anion bridges the two terminal copper atoms with a Cu(2)...Cu(2) distance of 4.770( 4) Angstrom. The angles Cu(2)-Cu(1)-Cu-2 and Cu(2)-Cl(1)-Cu(2) are 90. 0(1) and 144.4(4)degrees, respectively. The central Cu(1) exhibits a s quare pyramidal CuO5 co-ordination environment with four oxygen atoms of oximate groups in the basal plane and the water oxygen at the apica l site. The terminal Cu(2) atoms occupy the N-4 inner site of the liga nd with the chloride bridging anion occupying the axial position of th e square pyramidal CuN4Cl co-ordination environment. From magnetic sus ceptibility measurements, complex 2 was found to exhibit a very strong antiferromagnetic exchange interaction through the oximate bridges (J = -189 cm(-1)), leading to complete spin coupling at 120 K. Magnetic parameters are discussed on the basis of the structural results and co mpared with those other related complexes.