New, Multi-Dimensional Cu(tn)-[M(CN)6]n- Cyano-Bridged, Bimetallic Coordination Materials (M = FeII, CoIII, CrIII and tn = 1,3-Diaminopropane)

International audienceReaction of the [FeIII(CN)6]3– anion with [CuII(tn)(H2O)n]2+ (tn = 1,3-diaminopropane) affords the compounds [{CuII(tn)}2{FeII(CN)6}]·KCl·5H2O (1), [{CuII(tn)}2{FeII(CN)6}]·4H2O (2), and [{CuII(tnH)2(H2O)2}{FeII(CN)6}]·2H2O (3). Each iron center in 1 and 2 is linked to six copper(II) ions by six cyanide bridges, while each copper ion is linked to three equivalent iron(II) ions. Despite these resemblances, the two compounds present large structural differences caused by two different orientations of the Cu–NC–Fe bridges: compound 1 has a 2D structure which can be described as successions of “Cu4Fe3” defective cubane units, while compound 2 displays a 3D arrangement. Compound 3, in which only two trans-CN groups are bridging, displays a 1D structure. The tn ligand is chelating in 1, as is usually observed in several parent compounds, but is unexpectedly a bridging ligand in 2 and a terminal protonated tnH+ ligand in 3. Thus, the dimension of the three compounds seems to depend on the tn coordination modes. For the three iron compounds 1–3, the synthetic processes involve the spontaneous reduction of the paramagnetic [FeIII(CN)6]3– anion into the diamagnetic [FeII(CN)6]4– anion. In order to avoid such diamagnetic building blocks, the paramagnetic [Cr(CN)6]3– anion was used instead of the iron(III) analog, leading to [{CuII(tn)}3{CrIII(CN)6}2]·3H2O (4), which is the first 2D ferromagnet containing “-Cu–NC–Cr-” linkages. A similar study was performed using the diamagnetic [Co(CN)6]3– anion, leading to [{CuII(tn)}3{CoIII(CN)6}2]·3H2O (5), which is the Co analog of 4. The magnetic properties of compounds 1–3 and 5 show the presence of isolated CuII ions with weak ferromagnetic (1) or antiferromagnetic (2, 3, and 5) interactions. Compound 4 presents a long-range ferromagnetic ordering below Tc = 9.5 K