Controlled Synthesis of Heterotrimetallic Single‐Chain Magnets from Anisotropic High‐Spin 3 d–4 f Nodes and Paramagnetic Spacers

By using the node-and-spacer approach in suitable solvents, four new heterotrimetallic 1D chain-like compounds (that is, containing 3d–3d′–4f metal ions), {[Ni(L)Ln(NO3)2(H2O)Fe(Tp*)(CN)3]⋅2 CH3CN⋅CH3OH}n (H2L=N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane, Tp*=hydridotris(3,5-dimethylpyrazol-1-yl)borate; Ln=Gd (1), Dy (2), Tb (3), Nd (4)), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide- and phenolate-bridged heterotrimetallic chain, with a {FeCNNi(OLn)NC}n repeat unit. Within these chains, each [(Tp*)Fe(CN)3]− entity binds to the NiII ion of the [Ni(L)Ln(NO3)2(H2O)]+ motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO3)2(H2O)]+ unit is linked to two [(Tp*)Fe(CN)3]− ions through the NiII ion in a trans mode. In the [Ni(L)Ln(NO3)2(H2O)]+ unit, the NiII and LnIII ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1–4 are rare examples of 1D cyanide- and phenolate-bridged 3d–3d′–4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring FeIII and NiII ions through a cyanide bridge and between neighboring NiII and LnIII (except for NdIII) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single-chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d–4f heterotrimetallic single-chain magnets.