Structure and Magnetic Ordering of the Anomalous Layered (2D) Ferrimagnet [NEt 4 ] 2 Mn II 3 (CN) 8 and 3D Bridged‐Layered Antiferromagnet [NEt 4 ]Mn II 3 (CN) 7 Prussian Blue Analogues

The reaction of Mn II and [NEt 4 ]CN leads to the isolation of solvated [NEt 4 ]Mn 3 (CN) 7 ( 1 ) and [NEt 4 ] 2 Mn 3 (CN) 8 ( 2 ), which have hexagonal unit cells [ 1 : R $\bar 3$ m , a= 8.0738(1), c =29.086(1) Å; 2 : P $\bar 3$ m 1, a =7.9992(3), c =14.014(1) Å] rather than the face centered cubic lattice that is typical of Prussian blue structured materials. The formula units of both 1 and 2 are composed of one low‐ and two high‐spin Mn II ions. Each low‐spin, octahedral [Mn II (CN) 6 ] 4− bonds to six high‐spin tetrahedral Mn II ions through the N atoms, and each of the tetrahedral Mn II ions are bound to three low‐spin octahedral [Mn II (CN) 6 ] 4− moieties. For 2 , the fourth cyanide on the tetrahedral Mn II site is C bound and is terminal. In contrast, it is orientationally disordered and bridges two tetrahedral Mn II centers for 1 forming an extended 3D network structure. The layers of octahedra are separated by 14.01 Å ( c  axis) for 2 , and 9.70 Å ( c /3) for 1 . The [NEt 4 ] + cations and solvent are disordered and reside between the layers. Both 1 and 2 possess antiferromagnetic superexchange coupling between each low‐spin ( S =1/2) octahedral Mn II site and two high‐spin ( S =5/2) tetrahedral Mn II sites within a layer. Analogue 2 orders as a ferrimagnet at 27(±1) K with a coercive field and remanent magnetization of 1140 Oe and 22 800 emuOe mol −1 , respectively, and the magnetization approaches saturation of 49 800 emuOe mol −1 at 90 000 Oe. In contrast, the bonding via bridging cyanides between the ferrimagnetic layers leads to antiferromagnetic coupling, and 3D structured 1 has a different magnetic behavior to 2 . Thus, 1 is a Prussian blue analogue with an antiferromagnetic ground state [ T c =27 K from d( χT )/d T ].