Self-assembly of fish-bone and grid-like CoII-based single-molecule magnets using dihydrazone ligands with NNN and NNO pockets

Three Co^II complexes, [Co₂(H₂L¹)₂](ClO₄)₄·4CH₃OH (1), [Co₂(H₄L²)₂](ClO₄)₄ (2) and [Co₄(H₄L²)₄](ClO₄)₈ (3), were constructed by the self-assembly of the symmetrical dihydrazone ligands H2L1 and H4L2 with Co^II ions under different synthetic conditions. The fish-bone-like complex 1 was obtained using the ligand H2L1 in methanol via the solvothermal method, while the self-assembly of H4L2 with Co^II ions is solvent-dependent, producing the fish-bone-like complex 2 and [2 × 2] grid-like complex 3. Magnetic susceptibility measurements and theoretical calculations reveal that the large negative D values for the three complexes stem from their easy-axis magnetic anisotropy. Ac magnetic susceptibility measurements disclosed field-induced slow magnetic relaxation behaviors and the presence of Raman and/or direct processes of the three complexes at various applied dc fields.

Coordination-Directed Self-Assembly of Functional Polynuclear Lanthanide Supramolecular Architectures

Lanthanide supramolecular chemistry is a fast growing and intriguing research field due to the unique photophysical, magnetic, and coordination properties of lanthanide ions (Ln^III). Compared with the intensively investigated mononuclear Ln-complexes, polymetallic lanthanide supramolecular assemblies offer more structural superiority and functional advantages. In recent decades, significant progress has been made in polynuclear lanthanide supramolecules, varying from structural evolution to luminescent and magnetic functional materials. This review summarizes the design principles in ligand-induced coordination-driven self-assembly of polynuclear Ln-structures and intends to offer guidance for the construction of more elegant Ln-based architectures and optimization of their functional performances. Design principles concerning the water solubility and chirality of the lanthanide-organic assemblies that are vital in extending their applications are emphasized. The strategies for improving the luminescent properties and the applications in up-conversion, host-guest chemistry, luminescent sensing, and catalysis have been summarized. Magnetic materials based on supramolecular assembled lanthanide architectures are given in an individual section and are classified based on their structural features. Challenges remaining and perspective directions in this field are also briefly discussed.

Toroidal versus centripetal arrangement of the magnetic moment in a Dy4 tetrahedron

Magnetic investigation and ab initio calculations reveal toroidal arrangement of the magnetic moment rather than centripetal anisotropies in a tetrahedral Dy4 complex.

Anion-Dependent Structure and Luminescence Diversity in ZnII-LnIII Heterometallic Architectures Supported by a Salicylamide-Imine Ligand

To advance the structural development and fully explore the application potential, it is highly desirable but challenging to elucidate the relationship between the structures and properties of Zn^II-Ln^III heterometallic species. Herein, three types of Zn^II-Ln^III heterometallic compounds (Ln^III = Gd^III, Tb^III) formulated as [Zn₁₆Ln₄L₁₂(μ₃-O)₄(NO₃)₁₂]·8CH₃CN (ZnLn-1), [Zn₂Ln₂L₂(NO₃)₆(H₂O)₂]·3CH₃CN (ZnLn-2), and [Zn₄Ln₂L₈(OAc)₁₂]·xCH₃CN (ZnLn-3: for Ln = Gd, x = 5; for Ln = Tb, x = 4) were dictated by common inorganic anions, NO₃^- and OAc^-, with the aid of the multidentate ligand H₂L with propane as the central skeleton and 3-methoxysalicylamide and 3-methoxysalicylaldimine as terminal groups. ZnLn-1 features cubic cages with four {Zn₄L₃} tetrahedral subunits and four Ln³⁺ centers positioned at the eight vertices alternately when NO₃^- was introduced into the reaction system exclusively. An attempt to replace NO₃^- in ZnLn-1 with OAc^- partially led to the formation of {Zn₂Ln₂L₂} heterometallic wheels. Meanwhile, ZnLn-3 featuring double-hairpin-like {Zn₄Ln₂L₄} hemicycles that are orthogonal to each other assisted by intermolecular hydrogen bonds was constructed when NO₃^- in ZnLn-1 was completely replaced by OAc^-. Their structural integrity in solution were ascertained by both emission and ¹H NMR spectroscopy. Ascribed to the different Zn²⁺-containing antenna, ZnTb-2 possesses a relatively strong emission characteristic of Tb³⁺; ZnTb-1 has moderate Tb³⁺ luminescence, yet an absence of Tb³⁺ emission is found in ZnTb-3. Such an emission difference could be mainly attributed to the antenna effect directed by distinct structural characteristics induced by anions. The anion-dictated self-assembly strategy presented herein not only offers a facile approach to regulate the coordination mode of H₂L to such an extent to obtain diverse structures of Zn^II-Ln^III heterometallic species but also provides an understanding of how common inorganic anions tune coordination-driven self-assemblies as well as the subsequent luminescence properties.

Homochiral Dysprosium Phosphonate Nanowires: Morphology Control and Magnetic Dynamics

Controllable synthesis of uniformly distributed nanowires of coordination polymers with inherent physical functions is highly desirable but challenging. In particular, the combination of chirality and magnetism into nanowires has potential applications in multifunctional materials and spintronic devices. Herein, we report four pairs of enantiopure coordination polymers with formulae S-, R-Dy(cyampH)₃  ⋅ CH₃ COOH ⋅ 2H₂ O (S-1, R-1), S-, R-Dy(cyampH)₃  ⋅ 3H₂ O (S-2, R-2), S-, R-Dy(cyampH)₂ (C₂ H₅ COO) ⋅ 3H₂ O (S-3, R-3) and S-, R-Dy(cyampH)₃  ⋅ 0.5C₂ H₅ COOH ⋅ 2H₂ O (S-4, R-4) [cyampH₂ =S-, R-(1-cyclohexylethyl)aminomethylphosphonic acids], which were obtained depending on the pH of the reaction mixtures and the specific carboxylic acid used as pH regulator. Interestingly, compounds 3 were obtained as superlong nanowires, showing 1D neutral chain structure which contains both phosphonate and propionate anion ligands. While compounds 1, 2 and 4 appeared as block-like crystals, superhelices and nanorods, respectively, and exhibited similar neutral chain structures containing only phosphonate ligand. Slow magnetization relaxation characteristic of single-molecule magnet (SMM) behavior was observed for compounds S-1 and S-3. Theoretical calculations were performed to rationalize the magneto-structural relationships.