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

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Abstract
A new monodimensional µ-azido-nickel(II) complex of formula [{Ni2(Medien)2(µ1,1-N3)2(µ1,3-N3)}n][ClO4]n1 [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 1-D system. The magnetic behaviour corresponds to an alternating ferro-antiferromagnetic chain. The superexchange parameters have been calculated as JAF = –34.7 cm–1 and JFM = +38.2 cm–1, α = 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 α = JFM/|JAF|. Magnetic properties have been correlated to the structural data.