Phosphoraneiminato complexes of manganese and cobalt with heterocubane structure

The phosphraneiminato complexes [MnBr(NPEt3)](4) (1) and [M4Br5{NP(NMe2)(3) }(3)] with M = Mn (2) and M = Co (3) are prepared by melting reactions from the anhydrous metal dibromides with the silylated phosphaneimines Me3SiNPR 3 (R = Et, NMe2) in the presence of potassium fluoride. All complexes are c haracterized by crystal structure analyses. 1 forms an only slightly distor ted Mn4N4 heterocubane skeleton with an approximate T-d symmetry and short Mn ... Mn distances of average 295.7 pm. In the structures of 2 and 3 one m u(3)-NPEt3 ligand of 1 is replaced by one bromine atom with mu(3)-function. This leads to the novel heterocubane type M4N3Br with approximate C-3 symm etry. The deformation of the cubic skeleton leads to metal-metal distances of different lengths, i.e. 292.7 and 323.6 pm in 2 and 274.4 and 306.2 pm i n 3. Temperature dependent magnetic susceptibility measurements between 300 and 5 K on 1 have shown that strong antiferromagnetic coupling exists betw een the Mn(II) ions with S = 5/2, with a large negative Weiss constant of T heta = -694 K.