Ferromagnetic Interactions in the Mn(N(3))(4)[Ni(en)(2)(NO(2))](2) Trinuclear Compound. Crystal Structure and Physical Properties.

The goal of this work was to design a ferromagnetically coupled Mn(2+)Ni(2+) 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)NO(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) Å, b = 15.636(2) Å, c = 13.43(2) Å, beta = 90.14(6) degrees, and Z = 4. The structure consists of two very similar but crystallographically independent neutral trinuclear units with a MnNi(2) 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 Mn(2+)-Ni(2+) 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 Mn(2+) and Ni(2+) 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.