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

Abstract

An alternating di-(μ-(end-on)azido)−di-(μ-(end-to-end)azido) manganese(II) one-dimensional compound, with formula [Mn(bipy)(N3)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 P1̄ 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 MnII ions are alternatively bridged by two end-on (EO) and two end-to-end (EE) azido bridges. Each MnII 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 = −J1∑S2iS2i+1 − J2∑S2i+1S2i+2, are J1 = 13.8 K, J2 = −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.