Ferromagnetic interactions in the Mn(N3)4[Ni(en)2(NO2)]2 trinuclear compound.: Crystal structure and physical properties

The goal of this work was to design a ferromagnetically coupled Mn2+Ni2+ species. For this, we attempted to combine nitro-nitrito and end-on azido bridges which are both known to be ferromagnetic couplers. This has led us to the compound of formula Mn(N-3)(4)[Ni(en)(2)NO2](2) (en = ethylenediamine). The crystal structure has been solved at room temperature. The compound crystallizes in the monoclinic system, space group C2, with a = 12.631(14) Angstrom, b = 15.636(2) Angstrom, c = 13.43(2) Angstrom, beta = 90.14(6)degrees, and Z = 4. The structure consists of two very similar but crystallographically independent neutral trinuclear units with a MnNi2 isoceles triangular shape. The Mn and Ni atoms are doubly bridged by an end-on azido and a nitro-nitrito (with respect to Ni and Mn, respectively) group. Both the temperature dependence of the magnetic susceptibility and the field dependence of the magnetization at 2 K have been investigated and have revealed Mn2+-Ni2+ ferromagnetic interactions, which give rise to an S = 9/2 ground state for the triad. The quantitative interpretation of these magnetic properties has given an interaction parameter J between Mn2+ and Ni2+ ions equal to 1.4(1) cm(-1) (H = -JS(Mn).(S-Ni1 + S-Ni2) The electronic absorption spectrum has been recorded at various temperatures down to 20 K and interpreted.