Two-dimensional molecular-based ferrimagnets incorporating decamethylmetallocenium cations

Abstract

Four new molecular-based magnets have been synthesized, and their magnetic properties have been investigated in detail. Their formulae are [M′(C₅Me₅)₂]₂M₂[Cu(opba)]₃·(DMSO)_x(H₂O)_y with M′= Fe, M = Mn, x = 5, y = 4 (1), M′= Fe, M = Co, x = 6, y = 4 (2), M′= Co, M = Mn, x = 5.5, y = 4 (3) and M′= Co, M = Co, x = 5.5, y = 4 (4)[opba =ortho-phenylenebis(oxamato)]. The decamethylmetallocenium cations [Fe(C₅Me₅)₂]⁺ and [Co(C₅Me₅)₂]⁺ are most probably located between the anionic honeycomb-like networks Mn₂[Cu(opba)]₃ and Co₂[Cu(opba)]₃. Compounds 1–4 are two-dimensional ferrimagnets exhibiting a spontaneous magnetization below a critical temperature, T_c, of 14 K for 1, 27 K for 2, 13 K for 3 and 27.5 K for 4. Compounds 1 and 3, with Mn^II ions in the layered framework structure, do not exhibit magnetic hysteresis, while 2 and 4, with Co^II in the layered framework structure, exhibit a wide magnetic hysteresis loop. The coercive fields at 2 K are found to be equal to 3.5 × 10³ Oe for 2 and 5.3 × 103 Oe for 4. The latter is one of the largest values reported so far for a molecular-based magnet. The Mössbaer spectra for 1 and 2 have been recorded at various temperatures. These spectra suggest that the [Fe(C₅Me₅)₂]⁺ units occupy two sites between the layers with a 50/50 distribution, and that they are not directly involved in the long-range magnetic ordering.