Exploring the Magnetism of C₅/C₂B₃ Heteroleptic Organolanthanide Sandwiches

Two families of cyclopentadienyl (Cp)/carboranyl heteroleptic sandwiched organolanthanide complexes, namely [Ln{η⁵:σ-Me₂C(C₅H₄)(C₂B₁₀H₁₀)}₂][Li(DME)₃] (1Ln, Ln = Tb, Dy, Ho, Er) and [2-THF-2'-(μ²-Cl)Li(THF)₃-2,2'-Ln(nido-1,7-C₂B₉H₁₁)Cp*] (2Dy), were synthesized. Family of 1Ln has been proposed based on the mixing-ligands idea by linking Cp and nido-dicarborllide. However, the carborane cage of [Me₂C(C₅H₄)(C₂B₁₀H₁₀)]²⁻ deprotons and forms a mono-C⁻ anion rather than deboron to form dicarborllide dianion. Hence, the family of 1Ln features a dysprosocenium skeleton with extra two coordination of C⁻ anions of carborllides. Such coordination geometry is more like a tetrahedron if abstracting the centroids of two coordinated Cp rings. In this cubic-type geometry, no significant magnetic axiality is presented; only 1Dy and 1Tb show field-induced slow magnetic relaxation behavior below 10 K. Inspired by 1Ln, the free pentamethylcyclopentadienyl (Cp*⁻) and nido-dicarborllide ligands are used to sandwich central Dy³⁺ ion, achieving heteroleptic complex 2Dy. The bending angle by linking the centroid of Cp*⁻, Dy³⁺ and C₂B₃²⁻ in 2Dy is increased to 132.8(1)°. As such, the effective energy barrier for magnetic reversal (U_eff) and magnetic blocking temperature T_B (ZFC) are both increased (U_eff = 616(10) K; T_B = 6 K). The effort of further enhancing U_eff and T_B in such heteroleptic organolanthanide sandwiches should rely on keeping increasing the ligand axiality.