Size-Controlled Hapticity Switching in [Ln(C9H9)(C8H8)][Ln(C_{9}H_{9})(C_{8}H_{8})] Sandwiches

Sandwich complexes of lanthanides have recently attracted a considerable amount of interest due to their applications as Single Molecule Magnet (SMM). Herein, a comprehensive series of heteroleptic lanthanide sandwich complexes ligated by the cyclononatetraenyl (Cnt) and the cyclooctatetraenyl (Cot) ligand [Ln(Cot)(Cnt)] (Ln=Tb, Dy, Er, Ho, Yb, and Lu) is reported. The coordination behavior of the Cnt ligand has been investigated along the series and shows different coordination patterns in the solid-state depending on the size of the corresponding lanthanide ion without altering its overall anisotropy. Besides the characterization in the solid state by single-crystal X-ray diffraction and in solution by $^{1}H$NMR, static magnetic studies and ab initio computational studies were performed

Cyclic Structural Transformations from Crystalline to Crystalline to Amorphous Phases and Magnetic Properties of a Mn(II)-Based Metal–Organic Framework

A three-dimensional Mn­(II) framework, [Mn₂(H₂L)­(L)_0.5­(MeOH)­(DEF)]­·0.1MeOH­·0.1DEF­·1.4H₂O (<b>1</b>; H₄L = 2,3-dioxido-1,4-benzenedicarboxylic acid), was synthesized under solvothermal conditions in diethylformamide/methanol (DEF/MeOH), where the Mn centers adopt octahedral and unusual pentagonal bipyramidal geometries. The ligand H₄L was subject to deprotonation to create μ₄-H₂L^2– and μ₆-L^4– anionic bridges, leading to the construction of a coordination network. The MeOH exchange process of crystalline <b>1</b> allowed for another crystalline phase (<b>1a</b>), which reversibly returned to the original crystalline state upon resolvation in DEF/MeOH. After evacuation of <b>1a</b>, the amorphous phase <b>1b</b> was irreversibly formed, followed by the restoration of the original phase <b>1</b> upon resolvation in DEF/MeOH. Consequently, this framework underwent cyclic structural transformations from the crystalline (<b>1</b>) to crystalline (<b>1a</b>) to amorphous (<b>1b</b>) and back to crystalline (<b>1</b>) phase, which are unique transformations for soft coordination networks. Magnetic measurements demonstrated that antiferromagnetic interactions were operative between the Mn­(II) ions and were effectively mediated by the oxygen moieties of the μ₆-L^4– bridge

Control of Interchain Antiferromagnetic Coupling in Porous Co(II)-Based Metal–Organic Frameworks by Tuning the Aromatic Linker Length: How Far Does Magnetic Interaction Propagate?

Three MOF-74-type Co­(II) frameworks with one-dimensional hexagonal channels have been prepared. Co­(II) spins in a chain are ferromagnetically coupled through carboxylate and phenoxide bridges. Interchain antiferromagnetic couplings via aromatic ring pathways operate over a Co–Co length shorter than ∼10.9 Å, resulting in a field-induced metamagnetic transition, while being absent over lengths longer than ∼14.7 Å