Exchange interactions in carboxylate-bridged alternating chains of copper(II). Synthesis, crystal structure, spectroscopic and magnetic properties of catena-bis(N-salicylidene- l- methioninato)aquadicopper(II)

Abstract

The synthesis, crystal structure, spectroscopic and magnetic properties are reported for catena-bis(N-salicylidene- l-methioninato)aquadicopper(II), Cu-SALENMET. The compound crystallizes in the orthorhombic space group P2 12 12 1, with Z = 4. Lattice constants: a = 5.077(1), b = 13.229(1), c = 37.602(2) Å, and V = 2525(8) Å 3. Least- squares refinement of 171 parameters led to a final R = 0.052 for 1208 independent reflections having I > 3σ( I). The asymmetric unit consists of two copper atoms and two SALENMET (N-salicylidene- l-methioninato) groups. Each metal atom is directly attached to a single SALENMET group. The first of the two copper atoms has a (4+2) tetragonally elongated coordination geometry. The SALENMET group directly attached to it and the oxygen atom of a coordinated water molecule occupy four of the coordination sites. The coordination sphere is completed by two carboxylic oxygen atoms, one belongs to a SALENMET group of an adjacent ( x−1, y, z translation) asymmetric unit and the other belongs to the SALENMET group which is directly attached to the other copper atom within the asymmetric unit. This second copper atom has a (4 + 1) tetragonally elongated square pyramidal coordination geometry. Three of the coordination sites are occupied by the SALENMET group directly attached to it, one of them by the last above mentioned carboxylic oxygen atom. In this way, this oxygen atom is coordinated to both copper atoms within the asymmetric unit and the two SALENMET groups become linked through a CuOCu bridge. The coordination sphere is completed by two carboxylic oxygen atoms which belong to SALENMET groups of an adjacent asymmetric unit ( x−1, y, z translation). The crystal structure consists of discrete polymeric units generated only by translation along the crystallographic a axis. The polymeric units are built by bonds through adjacent asymmetric units as described above. Magnetic susceptibility data reveal antiferromagnetic interactions that may be described by the Heisenberg alternating-chain theory. The best fit of the magnetic susceptibility data yields value for the exchange coupling constant and alternation parameter, ( J, α) of −62.9 cm −1 and 0.58, respectively.