Structures and magnetism of cyano-bridged grid-like two-dimensional 4f-3d arrays

With the introduction of 4,4′-bipyridine N,N′-dioxide (bpdo) ligands, six novel cyano/bpdo mixed-bridged heterometallic 4f-3d compounds {{Ln(iii)(bpdo)(H₂O)₂M(iii)(CN)₆} ·2H₂O}_n (Ln = Nd(1), Sm(2), Gd(3), Tb(4) with M = Fe; Ln = Nd(5), Sm(6) with M = Co) have been prepared. X-Ray crystallography revealed that they have the same two-dimensional molecular structures, where each [M(CN)₆]^3- unit uses four co-planar cyanide groups to connect with four square anti-prism Ln³⁺ ions and, accordingly, each Ln³⁺ ion links four [M(CN)₆]^3- units, giving a corrugated grid-like layer and, simultaneously, the next nearest Ln ³⁺ ions are bridged by bpdo in the diagonal direction. Magnetic studies showed that the Ln³⁺-Fe³⁺ interaction is ferromagnetic for NdFe (1), antiferromagnetic for SmFe (2) and GdFe (3), while negligible for TbFe (4). Especially, 2 and 3 exhibited ferrimagnetic orderings below 2.9 and 1.9 K, respectively, with a coercive field of 40 Oe at 1.8 K for 2. Additionally, 5 showed an unusual field-induced magnetization relaxation.