Magnetic properties of a one-dimensional ferromagnet containing a Mn(III)-NC-Fe(III) linkage: Synthesis and crystal structure of a chainlike [Mn(acacen)Fe(CN)(6)](2n-)(n) polyanion

A one-dimensional compound with a Mn(III)-NC-Fe(III) linkage of the formula of [NEt(4)](2)[Mn(acacen)][Fe(CN)(6)] (NEt(4) = tetraethylammonium, acacen = N,N'-ethylenebis(acetylacetonylideneaminato)) has been prepared by the assembly reaction of [Mn(acacen)Cl] and [Et(4)](3)[Fe(CN)(6)] in ethanol/2-propanol. The compound crystallizes in the orthorhombic space group Pnma with the cell dimensions of a = 17.415(5) Angstrom, b = 19.79(1) Angstrom, c = 11.471(4) Angstrom, and Z = 4. The compound assumes a one-dimensional snaky-chain structure consisting of (-Mn-NC-Fe-CN-)(n) repeating units with dimensions of Fe-C = 1.952(4) Angstrom, Mn-N = 2.316(4) Angstrom, Mn-N-C = 152.6(3)degrees, Fe-C-N = 177.1(4)degrees, in which the Fe ion is positioned at the inversion center, the [Mn(acacen)] moiety lies on a mirror plane, and the adjacent one-dimensional chains run like a snake along the b axis with the same phase. On lowering of the temperature, the effective magnetic moment per FeMn increases gradually from 5.05 mu(B) at room temperature and then abruptly below ca. 20 K to 15.5 mu(B) at 1.9 K, indicating that the one-dimensional chain is a ferromagnetic chain due to an intrachain ferromagnetic coupling between Mn(III) and Fe(III) ions through the bridging CN- group. The FCM curve (field-cooled magnetization) under 1 Oe showed a spontaneous magnetization below 2.5 K. The magnetization vs H up to 55 kOe at 1.9 K showed an extremely large zero-field susceptibility, indicating that the compound is a ferromagnet due to a weak interchain ferromagnetic coupling.