Spontaneous Magnetization in Homometallic u6-oxalate Coordination Polymers

Reaction of 1,2,4-triazole and NaF with M(ox) (M = transition metal dication; ox = oxalate dianion) under hydrothermal conditions has lead to the isolation of a variety of hybrid organic-inorganic coordination polymers. Four structurally different 3D networks were obtained, depending on the transition metal, with stoichiometry: [M2(H2O)(m2-ox)][M2(m3-trz)6] (M = Fe (1), Co(2), Ni (3)), [Zn2(H2O)(m3-trz)2(m2-ox)] (4), [Mn3(m3-trz)2(m6-ox)(m3-F)2] (5) and [Fe3(m3-trz)2(m6-ox)(m2-F)2] (6). In all cases, the magnetic behavior is dominated by antiferromagnetic exchange interactions between paramagnetic centers. Remarkably, 5 and 6 present a novel magnetic connectivity around the oxalate anion: a 6-bridging mode. This magnetic geometry promotes multiple triangular arrangements among antiferromagnetically coupled spin carriers resulting in a complex magnetic network due to the presence of competing interactions. These materials exhibit spontaneous magnetization below 9 and 66 K, respectively.