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]n2n- 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 [NEt 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) Å, b = 19.79(1) Å, c = 11.471(4) Å, 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) Å, Mn−N = 2.316(4) Å, Mn−N−C = 152.6(3)°, Fe−C−N = 177.1(4)°, 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 μ B at room temperature and then abruptly below ca. 20 K to 15.5 μ 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.