Single-Molecule Magnet Rods: Remarkably Elongated Lanthanide Phosphonate Cores with Quasilinear Hydrazones

Large metal-phosphonate clusters typically exhibit regular polyhedral, wheel-shaped, spherical, or capsule-shaped morphologies more effectively than high-aspect ratio topologies. A system of elongated lanthanide core topologies has now been synthesized by the reaction of lanthanide 1-naphthylmethylphosphonates and four differently terminated pyrazinyl hydrazones. Four new rod-shaped dysprosium phosphonate clusters, [Dy₆(O₃PC₁₁H₉)₄(L¹)₄(μ₄-O)(DMF)₄]·2DMF·3MeCN·3H₂O (<b>1</b>), [Dy₈(O₃PC₁₁H₉)₄(L²)₄(μ₃-O)₄(CO₂)₄(H₂O)₄]·6DMF·4MeCN·3H₂O (<b>2</b>), [Dy₁₂Na(O₃PC₁₁H₉)₆(L³)₆(μ₃-O)₂(pyr)₆]·DMF·2MeCN·H₂O (<b>3</b>), and [Dy₁₄(O₃PC₁₁H₉)₁₂(L⁴)₈(μ₃-O)₂(DMF)₄(MeOH)₂(H₂O)₄]·5DMF·2MeCN·H₂O (<b>4</b>), were obtained. Four single-pyrazinyl hydrazones function as pentadentate bis-chelate terminal co-ligands, coordinating the periphery of dysprosium phosphonate rods. A sodium ion serves as a cation template for constructing heterobimetallic <b>3</b> by occupying the void, demonstrating the ability to reliably control cluster length by modifying the hydrazone co-ligand structure and cation template. Additionally, it was observed that the elongation of the rods has a significant directional impact on the magnetic relaxation behavior, transitioning from a one-step process in <b>1</b> to a three-step process in <b>2</b>, a two-step process in <b>3</b>, and finally a two-step process in <b>4</b>.