Structure and magnetic behaviour of the one-dimensional [{Ni2(Medien)2(μ1,1-N3)2(μ1,3-N3)}n][ClO4]n compound with unusually strong ferro-antiferromagnetic alternating interactions

A new mo no dimensional mu-azido-nickel(II) complex of formula [{Ni-2(Medien)(2)(mu(1,1)-N-3)(2)(mu(1,3)-N-3)}(n)][ClO4](n) 1 [Medien = bis(2-aminoethyl)methylamine] has been synthesized and crystallographically characterised. The nickel atom is placed in an octahedral environment bridged by two end-on azido ligands and one end-to-end azido bridge to the neighbouring nickel atoms, giving an alternated I-D system. The magnetic behaviour corresponds to an alternating ferro-antiferromagnetic chain. The superexchange parameters have been calculated as J(AF) = -34.7 cm(-1) and J(FM) = +38.2 cm(-1), a = 1.10, by means of an improved analytical expression for the magnetic susceptibility of the isotropic ferro-antiferromagnetic S = 1 Heisenberg chain in terms of the alternation parameter a = J(FM)/\J(AF)\. Magnetic properties have been correlated to the structural data.