Controlled Synthesis of Heterotrimetallic Single-Chain Magnets from Anisotropic High-Spin 3d-4f 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)]center dot 2CH(3)CN center dot 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 {-Fe-C N-Ni(-O-Ln)-N C-}(n) repeat unit. Within these chains, each [(Tp*)Fe(CN)(3)](-) entity binds to the Ni-II 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 Ni-II ion in a trans mode. In the [Ni(L)Ln(NO3)(2)(H2O)](+) unit, the Ni-II and Ln(III) 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 Fe-III and Ni-II ions through a cyanide bridge and between neighboring Ni-II and Ln(III) (except for Nd-III) 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.