Functionalized Triptycene-Derived Tripodal Ligands: Privileged Formation of Tetranuclear Cage Assemblies with Larger Ln(III)

Triptycene-based diiron(II) mesocates: spin-crossover in solution

Triptycene-based diiron(II) and dizinc(II) mesocates were obtained using a novel rigid ligand with two pyridylbenzimidazole chelating units fused into the triptycene scaffold. Studies on the diiron(II) assembly in solution showed that the complex undergoes thermal-induced one-step spin-crossover with T1/2 at 243 K (Evans method).

Ligand Chirality Transfer from Solution State to the Crystalline Self-Assemblies in Circularly Polarized Luminescence (CPL) Active Lanthanide Systems

The synthesis of a family of chiral and enantiomerically pure pyridyl-diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid-state structures of these chiral metallosupramolecular systems are determined using X-ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL-LSCM) where the two enantiomers can be clearly distinguished.

Hydrogen Peroxide Disproportionation Activity Is Sensitive to Pyridine Substitutions on Manganese Catalysts Derived from 12-Membered Tetra-Aza Macrocyclic Ligands

The abundance of manganese in nature and versatility to access different oxidation states have made manganese complexes attractive as catalysts for oxidation reactions in both biology and industry. Macrocyclic ligands offer the advantage of substantially controlling the reactivity of the manganese center through electronic tuning and steric constraint. Inspired by the manganese catalase enzyme, a biological catalyst for the disproportionation of H2O2 into water and O2, the work herein employs 12-membered tetra-aza macrocyclic ligands to study how the inclusion of and substitution to the pyridine ring on the macrocyclic ligand scaffold impacts the reactivity of the manganese complex as a H2O2 disproportionation catalyst. Synthesis and isolation of the manganese complexes was validated by characterization using UV-vis spectroscopy, SC-XRD, and cyclic voltammetry. Potentiometric titrations were used to study the ligand basicity as well as the thermodynamic equilibrium with Mn(II). Manganese complexes were also produced in situ and characterized using electrochemistry for comparison to the isolated species. Results from these studies and H2O2 reactivity showed a remarkable difference among the ligands studied, revealing instead a distinction in the reactivity regarding the number of pyridine rings within the scaffold. Moreover, electron-donating groups on the 4-position of the pyridine ring enhanced the reactivity of the manganese center for H2O2 disproportionation, demonstrating a handle for control of oxidation reactions using the pyridinophane macrocycle.

Synthesis and Characterization of Lanthanide Metal Ion Complexes of New Polydentate Hydrazone Schiff Base Ligand

The new homodinuclear complexes of the general formula [Ln₂L₃(NO₃)₃] (where HL is newly synthesized 2-((2-(benzoxazol-2-yl)-2-methylhydrazono)methyl)phenol and Ln = Sm³⁺ (1), Eu³⁺ (2), Tb³⁺ (3a, 3b), Dy³⁺ (4), Ho³⁺ (5), Er³⁺ (6), Tm³⁺ (7), Yb³⁺ (8)), have been synthesized from the lanthanide(III) nitrates with the polydentate hydrazone Schiff base ligand. The flexibility of this unsymmetrical Schiff base ligand containing N₂O binding moiety, attractive for lanthanide metal ions, allowed for a self-assembly of these complexes. The compounds were characterized by spectroscopic data (ESI-MS, IR, UV/Vis, luminescence) and by the X-ray structure determination of the single crystals, all of which appeared to be different solvents. The analytical data suggested 2:3 metal:ligand stoichiometry in these complexes, and this was further confirmed by the structural results. The metal cations are nine-coordinated, by nitrogen and oxygen donor atoms. The complexes are two-centered, with three oxygen atoms in bridging positions. There are two types of structures, differing by the sources of terminal (non-bridging) coordination centers (group A: two ligands, one nitro anion/one ligand, two nitro anions, group B: three ligands, three anions).

Capturing the Trajectory of Metal-Ion-Cluster Formation: Stepwise Accumulation of Zn(II) Ions in a Robust Coordination Space Formed by a Rigid Tridentate Carboxylate Ligand

Organic ligand-directed synthesis of metal-ion clusters with a well-defined number and arrangement of metal ions is an important subject toward the development of functional inorganic-organic nanohybrids. Here we report the synthesis of multinuclear Zn-oxo clusters using a triptycene-based rigid ligand (H₃L) featuring three metal-coordination sites arranged in a triangular shape. Upon complexation of H₃L with zinc acetate dihydrate, a decanuclear Zn-oxo cluster and multinuclear Zn-oxo clusters with a smaller number of Zn(II) ions were formed as the final product and its intermediates, respectively. A comparison of the X-ray structure of the final product with those of the intermediates revealed the cluster-formation process, where four triptycene ligands preorganize to form a robust coordination space to which Zn(II) ions accumulate in a stepwise manner. This stepwise metal-ion accumulation, along with the formation of a large tetrahedral decanuclear Zn-oxo cluster, highlights the potential of ligand design using 1,8,13-substituted triptycenes for the development of various metal-ion clusters.

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.

Triple-stranded triptycene-based metallo-supramolecular helicate displaying efficient encapsulation of bulky guest molecules

Triple-stranded metallo-supramolecular helicates were readily constructed by achieving a coordination of the gallium(iii) cation by ligands based on 2,7- and 2,6-disubstituted triptycenes. The significance of these building blocks in the construction of helicates with the capability for guest encapsulation was also revealed.

Radii-dependent self-assembly polynuclear lanthanide complexes as catalysts for CO2 transformation into cyclic carbonates

A series of lanthanide complexes with structural variation from a dinuclear to pentanuclear structure are found to be dependent on the radii of Ln3+ ions, and show high catalytic performance to obtain cyclic carbonates under solvent-free conditions.

Formation of Heteropolynuclear Lanthanide Complexes Using Macrocyclic Phosphonated Cyclam-Based Ligands

Ligands L₁ and L₂, respectively based on a cyclam and a cross-bridged cyclam scaffold functionalized at N1 and N8 by 6-phosphonic-2-methylene pyridyl groups, are described. While complexation of lanthanide (Ln) cations with L₂ was not possible, a family of complexes has been prepared with L₁, of the general formulae [LnL₁H₂]Cl (Ln³⁺ = Lu, Tb, Yb) or [LnL₁H] (Ln³⁺ = Eu). The solution, structural, potentiometric, and photophysical data for these novel ligands and their complexes have been investigated, including a solid-state study by X-ray diffraction (L₁, L₂, and [EuL₁H]), ¹H NMR complexation investigations (Lu³⁺), as well as UV-vis absorption and luminescence spectroscopy in water and D₂O (pH ≈ 7). L₁ forms 1:1 metal-ligand stoichiometric octadentate complexes in solution. Importantly, the pyridyl phosphonate functions are capable of simultaneous chelation to the metal center and of interaction with a second metal center. ¹H NMR (Lu³⁺) and spectrophotometric titrations of the isolated [TbL₁]^- complex by EuCl₃ salts demonstrated the formation of high-order (hetero)polymetallic species in aqueous solution (H₂O, pH = 7). Global analysis of the luminescence titration experiment points to the formation of 4:1, 3:1, and 3:2 [TbL₁]/Eu heteropolynuclear assemblies, exhibiting a strong preference to forming [TbL₁]₃Eu₂ at increased europium concentrations, with energy transfer occurring between the kinetically inert terbium complex and added europium cations.

Eu(III) Tetrahedron Cage as a Luminescent Chemosensor for Rapidly Reversible and Turn-On Detection of Volatile Amine/NH3

Because of the involvement of the gas-solid diffusion, device fabrication, and the relatively complex photophysical process, the lanthanide complexes are rarely exploited as fluorescence sensors for volatile compound (VC) detection. Herein, we report the first example of a discrete 3D Ln-based architecture as a sensor for VCs. The designed Eu₄L₄ tetrahedral cage shows highly selective, rapidly reversible, and turn-on emissive responses toward volatile amines/NH₃ in a spin-coated film. Through the comprehensive spectral characteristic and density functional theory calculation, an intermolecular weak nucleophilic interaction is proposed for this response mechanism. Combining this weak interactions with the permeability of the cage, the film presents subsecond to second timescales rapid response; combining the fitting electrophilic capability of the β-diketonate units to amine nitrogen with the tunable intramolecular charge-transfer feature, the cage shows excellent selectivity and turn-on emissive response. This work provides a new clue to develop the lanthanide complexes as luminescence probes for VCs.

Two [Ln4] molecular rings folded as compact tetrahedra

A new highly photo-switchable ligand furnishes supramolecular tetrahedral nanomagnets with Ln(iii) ions (Ln = Dy, Tb). Intramolecular weak interactions define the conformation of the ligand, quenching the photochromic activity.

Chiral luminescent lanthanide complexes possessing strong (samarium, SmIII) circularly polarised luminescence (CPL), and their self-assembly into Langmuir-Blodgett films

The lanthanide directed self-assembly of chiral amphiphilic 2,6-pyridinedicarboxylic acid based ligands 1 and 2 with various Ln(CF₃SO₃)₃ (Ln = Tb^III, Sm^III, Lu^III, Dy^III) salts was studied in CH₃CN and evaluated with the expected 1 : 3 and 1 : 1 Ln : Ligand species forming in solution. Ligand chirality was retained and transferred, as depicted by circular dichroism (CD) and circularly polarised luminescence (CPL) measurements (for Tb^III and Sm^III), to the lanthanide centre upon complexation with high dissymmetry factor values for the Sm^III complexes obtained (g_lum = -0.44 and 0.29 and 0.45 and -0.23 for the ⁴G_5/2→⁶H_5/2 and the ⁴G_5/2→⁶H_7/2 transitions of Sm·1₃ and Sm·2₃, respectively). The ability of the complexes to form stable Langmuir monolayers at the air-water interface was also established while Langmuir-Blodgett films of Tb·L₃ and Sm·L₃ exhibited lanthanide luminescent emission.

Optically active triptycenes containing hexa-peri-hexabenzocoronene units

We have successfully generated both left- and right-handed circularly polarized light using crystals prepared from a racemic triptycene containing hexa-peri-hexabenzocoronene units.

Circularly Polarized Luminescent Triptycene-Based Polymers

A series of chiral fluorescent polymers containing optically active triptycene units in the main chain were synthesized via Sonogashira-Hagihara coupling copolymerizations of (R,R)- or (S,S)-2,6-diethynyltriptycene with a range of diiodoaryls. Their optical and chiroptical properties were investigated under various solution conditions. We observe that these polymers emitted circularly polarized light owing to the chiral triptycene framework with a handed twisted rigid structure, and the fluorescence colors could be tuned in the whole visible range from blue to red by replacing the achiral comonomer units. They possessed luminescence dissymmetry factors of approximately 1.0 × 10^-3, regardless of the incorporated comonomer units.

[Ag15(N-triphos)4(Cl4)](NO3)3: a stable Ag-P superatom with eight electrons (N-triphos = tris((diphenylphosphino)methyl)amine)

A first and stable Ag-P superatom nanocluster [Ag₁₅(N-triphos)₄(Cl₄)](NO₃)₃ (1) has been successfully synthesized and characterized. X-ray analysis shows that this Ag₁₅ cluster has a hexacapped body-centered cubic (bcc) framework which is consolidated by four tripodal N-triphos ligands. The identity of 1 is confirmed by high resolution ESI-MS. Cluster 1 has an electronic and geometric shell closure structure with 8 free electrons, matching the stability idea of superatom theory for a nanocluster. DFT calculation of this Ag₁₅ cluster reveals the superatom feature with a 1S²1P⁶ configuration. The chelation of multidentate phosphines enhances the stability of this Ag₁₅ cluster. The AgAg distances between the centered and the vertical Ag atoms of this bcc (Ag@Ag₈) are in the range of 2.57-2.71 Å, and the distances between the face-capped and the vertical silver atoms are in the range of 2.84-2.92 Å, showing strong AgAg interactions within this cluster core. This superatom complex exhibits a relatively high thermal and photolytic stability.

Ln(iii) complexes with triptycene based tripodal ligands: speciation and equilibria

The speciation studies of Ln(iii) complexes with triptycene-based tripodal ligands reveal slow transformations of tetranuclear assemblies in metal excess.

Chiral triptycene-pyrene π-conjugated chromophores with circularly polarized luminescence

Novel chiral triptycenes showing circularly polarized luminescence based on the supramolecular chirality induced in the hydrogen-bonded aggregate have been developed.