New, Multi‐Dimensional Cu(tn)‐[M(CN) 6 ] n – Cyano‐Bridged, Bimetallic Coordination Materials (M = Fe II , Co III , Cr III and tn = 1,3‐Diaminopropane)

Reaction of the [Fe III (CN) 6 ] 3– anion with [Cu II (tn)(H 2 O) n ] 2+ (tn = 1,3‐diaminopropane) affords the compounds [{Cu II (tn)} 2 {Fe II (CN) 6 }] · KCl · 5H 2 O ( 1 ), [{Cu II (tn)} 2 {Fe II (CN) 6 }] · 4H 2 O ( 2 ), and [{Cu II (tnH) 2 (H 2 O) 2 }{Fe II (CN) 6 }] · 2H 2 O ( 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 “Cu 4 Fe 3 ” 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 [Fe III (CN) 6 ] 3– anion into the diamagnetic [Fe II (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 [{Cu II (tn)} 3 {Cr III (CN) 6 } 2 ] · 3H 2 O ( 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 [{Cu II (tn)} 3 {Co III (CN) 6 } 2 ] · 3H 2 O ( 5 ), which is the Co analog of 4 . The magnetic properties of compounds 1 – 3 and 5 show the presence of isolated Cu II ions with weak ferromagnetic ( 1 ) or antiferromagnetic ( 2 , 3 , and 5 ) interactions. Compound 4 presents a long‐range ferromagnetic ordering below T c = 9.5 K.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)