Soft and hard molecule-based magnets of formula [(Etrad)(2)M-2{Cu(opba)}(3)]center dot S [Etrad(+) = radical cation, M-II = Mn-II or Co-II, opba = Ortho-phenylenebis(oxamato), S = solvent molecules], with a fully interlockedstructure

The goal of this work was to explore the chemistry and the physics of a fam ily of molecule-based magnets containing three spin carriers, with a fully interlocked structure. The main emphasis was on the coercivity of these mag nets, which confers a memory effect on the materials. For this, three compo unds have been synthetized, namely the precursor [(Etrad)(2)Cu(opba)]. CH3C N . H2O (1), and the magnets [(Etrad)(2)Mn-2{Cu(opba)}(3)(DMSO)(0.5)]. 0.25 H(2)O (2) and [(Etrad)(2)Co-2{Cu(opba)}(3)(DMSO)(1.5)]. 0.25H(2)O (3), wher e Etrad(+) stands for the radical cation 2-(1-ethylpyridinium-4-yl)-4,4,5,5 -tetramethylimidazolin-1-oxyl-3-oxide, and opba stands for ortho-phenyleneb is(oxamato). The crystal structures of the three compounds have been determ ined. The structure of 1 consists of planar Cu(opba) units with one of the radical cations weakly bound to the Cu2+ ion, the other radical cation bein g rather isolated. Compounds 2 and 3 are isomorphous. Their structure consi sts of two interpenetrating graphitelike networks with edge-sharing hexagon s. The magnetic properties of the three compounds have been investigated in detail. For compounds 2 and 3 the temperature dependences of the direct cu rrent (dc) and alternating current (ac) magnetic responses have been measur ed along with the field dependence of the mag netization. Both compounds ex hibit a long-range magnetic ordering with a spontaneous magnetization. The critical temperatures are 22.8 K and 37 K for 2 and 3, respectively. While 2 is a soft magnet, 3 has been found to be a very hard magnet, with a coerc ive field depending on the particle size. This coercive field may reach 24 kOe at 6 K for a sample consisting of very small crystals. Mixed materials with the abbreviated formula [Etrad(2)Mn(2-2x)Co(2x)Cu(3)] (4-x) have also been synthesized. Their critical temperatures have been found to vary almos t Linearly with x. The x dependence of the coercive field has also been inv estigated and analyzed.