Alternating Ferromagnetic−Antiferromagnetic Interactions in a Manganese(II)−Azido One-Dimensional Compound:  [Mn(bipy)(N₃)₂]

An alternating di-(μ-(end-on)azido)−di-(μ-(end-to-end)azido) manganese(II) one-dimensional compound, with formula [Mn(bipy)(N 3 ) 2 ] (bipy = 2,2‘-bipyridine), has been synthesized and characterized. Its crystal structure has been solved at room temperature. The complex crystallizes in the triclinic P 1̄ space group, with a = 7.547(2) Å, b = 9.137(4) Å, c = 9.960(4) Å, α = 110.76(4)°, β = 104.43(2)°, γ = 100.41(3)°, and Z = 2. The structure consists of manganese chains in which the Mn II ions are alternatively bridged by two end-on (EO) and two end-to-end (EE) azido bridges. Each Mn II ion has an octahedral coordination, completed by the two nitrogen atoms of the bipy ligand. The EO and EE bridges are arranged cis . This constitutes the first example of such an azido bridge chain for any metallic ion. ESR measurements show signals corresponding to ΔMs = 1 and ΔMs = 2 transitions, with no significant variations by modifying the temperature. The thermal variation of molar susceptibility reveals the existence of alternating ferro- and antiferromagnetic interactions, through alternating EO and EE azido bridges, in the compound. A theoretical model has been developed for an S = 5 / 2 alternating ferromagnetic−antiferromagnetic coupled 1D system: the exchange parameters obtained with this model, considering the spin Hamiltonian H = − J 1 ∑ S 2 i S 2 i +1 − J 2 ∑ S 2 i +1 S 2 i +2, are J 1 = 13.8 K, J 2 = −17.01 K with g fixed at 2.0. Extended Hückel calculations are discussed to model the end-on and end-to-end bridged systems.