Self-Assembly of Luminescent Lanthanide Mesocates as Efficient Catalysts for Transforming Carbon Dioxide into Cyclic Carbonates

Self-Assembly of Rhenium(I) Double-Stranded Helicate and Mesocate from Flexible Ditopic Benzimidazolyl/Naphthanoimidazolyl N-Donor and Rigid Bis-Chelating Hydroxyphenylbenzimidazolyl N∩OH-Donor Ligands: Synthesis, Characterization, and Photophysical and B-DNA Docking Studies

The self-assembly of three rheniumtricarbonyl core-based supramolecular coordination complexes (SCCs), fac-[Re(CO)3(μ-L)(μ-L')Re(CO)3] (1-3) was carried out using Re2(CO)10, rigid bis-chelating ligand (HO∩N-Ph-N∩OH (L1) (where HO∩N = 2-hydroxyphenylbenzimidazolyl), and flexible ditopic N-donor ligands (L2 = bis(3-((1H-benzoimidazol-1-yl)methyl)-2,4,6-trimethylphenyl)methane, L3 = bis(3-((1H-naphtho[2,3-d]imidazol-1-yl)methyl)-2,4,6-trimethylphenyl)methane, L4 = bis(4-(naphtho[2,3-d]imidazol-1-yl-methyl)phenyl)methane) via a one-pot solvothermal approach. In the solid state, the dinuclear SCCs adopt heteroleptic double-stranded helicate and meso-helicate architectures. The supramolecular structures of the complexes are retained in the solution based on the 1H NMR and electrospray ionization (ESI)-mass analysis. The spectral and photophysical properties of the complexes were studied both experimentally and using time-dependent density functional theory (TDDFT) calculations. All of the supramolecules exhibited emission in both solution and solid states. Theoretical studies were conducted to determine the chemical reactivity parameters, molecular electrostatic potential surface plots, natural population, and Hirshfeld analysis for complexes 1-3. Additionally, molecular docking studies were carried out for complexes 1-3 with B-DNA.

Two Synthetic Approaches to Coinage Metal(I) Mesocates: Electrochemical versus Chemical Synthesis

We report two different approaches to isolate neutral and cationic mesocate-type metallosupramolecular architectures derived from coinage monovalent ions. For this purpose, we use a thiocarbohydrazone ligand, H₂L (1), conveniently tuned with bulky phosphine groups to stabilize the M^I ions and prevent ligand crossing to achieve the selective formation of mesocates. The neutral complexes [Cu₂(HL)₂] (2), [Ag₂(HL)₂] (3), and [Au₂(HL)₂] (4) were prepared by an electrochemical method, while the cationic complexes [Cu₂(H₂L)₂](PF₆)₂ (5), [Cu₂(H₂L)₂](BF₄)₂ (6), [Ag₂(H₂L)₂](PF₆)₂ (7), [Ag₄(HL)₂](NO₃)₂ (8), and [Au₂(H₂L)₂]Cl₂ (9) were obtained by using a metal salt as the precursor. All of the complexes are neutral or cationic dinuclear mesocates, except the silver nitrate derivative, which exhibits a tetranuclear cluster mesocate architecture. The crystal structures of the neutral and cationic copper(I), silver(I), and gold(I) complexes allow us to analyze the influence of synthetic methodology or the counterion role on both the micro- and macrostructures of the mesocates.

Strong Circularly Polarized Luminescence at 1550 nm from Enantiopure Molecular Erbium Complexes

Circularly polarized luminescence (CPL) in two subregions of the near-infrared (NIR) has been achieved. By leveraging the rigidity and diminishing detrimental vibrations of the heterobimetallic binolate complexes of erbium [(Binol)₃ErNa₃], species exhibiting an exceptionally high dissymmetry factor (|g_lum |) of 0.47 at 1550 nm were obtained. These erbium complexes are the first reported examples of CPL observed beyond 1200 nm. Analogous complexes of ytterbium and neodymium also exhibited strong CPL (|g_lum| = 0.17, 0.05, respectively) in a higher energy NIR window (800-1200 nm). All complexes exhibit high quantum yields (Er: 0.58%, Yb: 17%, Nd: 9.3%) and high B_CPL values (Er: 57 M^-1 cm^-1, Yb: 379 M^-1 cm^-1, Nd: 29 M^-1 cm^-1). Because of their strong CPL emission in the telecom band (1550 nm), biologically relevant NIR emission window (800-1100 nm), and synthetic versatility, the complexes reported here could permit further promising developments in quantum communication technologies and biologically relevant sensors.

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.

Base- and Metal-Dependent Self-Assembly of Lathanide-Organic Coordination Polymers or Macrocycles with Tetradentate Acylhydrazone-based Ditopic Ligands

Herein, we report a comprehensive study on the lanthanide-directed coordination self-assembly with two bis-tetradentate acylhydrazone ligands H₄ L¹ and H₄ L² . Multifarious outcomes, which are base- and metal-dependent, were revealed by NMR, ESI-TOF-MS and X-ray crystallography. In the absence of base, bent H₄ L¹ was assembled into dinuclear double-strand helicate Ln₂ (H₂ L¹ )₂ by partially-deprotonated assembly with La, Sm or Eu, while trinuclear Ln₃ (H₂ L¹ )₃ with Yb or Lu. For linear H₄ L² , infinite 1D zig-zag metal-organic polymeric chain (Ln₂ H₂ L² )_n was obtained. However, complete deprotonated L¹ and L² assembled into discrete trinuclear Ln₃ (L^{1 /2} )₃ and tetranuclear Ln₄ (L^{1 /2} )₄ macrocyclic structures under the basic condition. For these, there are multiple possible isomers coexisting in the solution which were enumerated and simulated with molecular mechanic modeling. Visible-light sensitized NIR emissions on the Yb complexes have been observed, endowing them potential application in photofunctional materials.

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.

Cerium Pyrazolates Grafted onto Mesoporous Silica SBA-15: Reversible CO2 Uptake and Catalytic Cycloaddition of Epoxides and Carbon Dioxide

The activation and catalytic conversion of CO₂ is a current topic relating to molecular chemistry and materials science alike. As a transdisciplinary field of research, surface organometallic chemistry (SOMC) might be applicable to perform synergistically, thus striking a new path in sustainable chemistry. Both ceric and cerous rare-earth-metal pyrazolates, which were recently shown to reversibly insert CO₂ and to promote the catalytic cycloaddition of epoxides and carbon dioxide, were grafted onto large-pore mesoporous silica SBA-15₅₀₀, thermally pretreated at 500 °C. The obtained hybrid materials [Ce(Me₂pz)₄]₂@SBA-15₅₀₀, Ce(Me₂pz)₄(thf)@SBA-15₅₀₀, Ce₄(Me₂pz)₁₂@SBA-15₅₀₀, and [Ce(Me₂pz)₃(thf)]₂@SBA-15₅₀₀ (Me₂pz = 3,5-dimethylpyrazolato) were characterized by DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy), solid-state ¹H/¹³C NMR spectroscopy, elemental analysis, ICP/OES, and N₂ physisorption. The lanthanum(III)-based material [La(Me₂pz)₃(thf)]₂@SBA-15₅₀₀ was synthesized for better assessment of the cerous materials being highly sensitive to oxidation. To mimic ceric surface species, Ce[OSi(OtBu)₃]₃Cl was treated with 1 equiv of K(Me₂pz), generating the mixed pyrazolyl/siloxy complex KCe[OSi(OtBu)₃]₄(Me₂pz) featuring a cerium(IV)-bonded terminal pyrazolato ligand. All hybrid materials show efficient and reversible carbon dioxide uptake of maximum 20 wt % in the solid state. When combined with tetra-n-butylammonium bromide (TBAB), the hybrid materials catalyze the cycloaddition of CO₂ and epoxides, displaying good conversion of various epoxides and reusability.

Self-assembly of tetranuclear 3d–4f helicates as highly efficient catalysts for CO2 cycloaddition reactions under mild conditions

A series of 4-nuclear lanthanide clusters supported by organic ligands Zn3LnL4 (Ln = Dy(1), Gd(2), Er(3)) were synthesized. These helicates could be used to convert CO₂ into cyclic carbonates with TOF up to 38 000 h⁻¹, without being influenced by moisture or air.

Carbonyl group and carbon dioxide activation by rare-earth-metal complexes

The rare-earth elements (Ln = Sc, Y, La-Lu) are widely used in stoichiometric and catalytic carbonyl group transformations. Sufficient availability, non-toxicity, high oxophilicity, tunable ion size/Lewis acidity and enhanced ligand exchangeability have been major driving factors for their successful implementation. Routinely employed reagents for stoichiometric carbonyl group transformations are divalent ytterbium and samarium compounds (e.g., ketone reduction), bimetallic CeCl3/LiR (C-C coupling), or ceric ammonium nitrate CAN (cyclic ketone oxidation). Rare-earth-metal triflates, and in particular Sc(OTf)3, are prominent examples of Lewis acid catalysts for versatile use in organic synthesis (e.g., Aldol and Michael reactions). Moreover, Ln(ii) and Ln(iii) complexes efficiently catalyze the (co)polymerization of carbonyl group-containing monomers including lactones, lactides, acrylates, and carbon dioxide. Featuring the most notorious greenhouse gas, CO2 is currently assessed as a cheap, abundant, and non-toxic C1 building block. Ln(iii) complexes are not only capable of efficient CO2 capture via reversible insertion but also of CO2 activation for catalytic conversions (copolymerization/cycloaddition with epoxides). This perspective focuses on structurally elucidated Ln complexes resulting from ketone or carbonyl derivative activation/insertion as well as carbon dioxide insertion products. The respective compounds will be sorted by structural motifs and, if applicable, details on reactivity and feasibility of catalytic reactions are presented. The article is subdivided in three parts: (i) donor and insertion products of ketones and aldehydes, (ii) redox-enhanced activation of carbonyl derivatives, and (iii) CO2 insertion/redox products and homogeneous catalytic conversion.

Monometallic lanthanide salicylhydrazone complexes exhibiting strong near-infrared luminescence

We report the synthesis of monometallic lanthanide complexes supported by one salicylhydrazone ligand. Complexes of neodymium, erbium, and ytterbium have been synthesized, and exhibit near infrared luminescence with modest to high quantum yields. The luminescence of ytterbium is increased by a factor of five when comparing our complex to other salicylhydrazone-supported complexes.

Metallopolymers cross-linked with self-assembled Ln4L4 cages

Herein, we report a metallopolymer based on a polydivinylbenzene (PDVB) matrix cross-linked by tetranuclear Ln₄L₄ cages.

Synthesis, structure, photoluminescent, optical and magnetic properties of a novel thulium p-hydroxybenzenesulfonate complex

A novel thulium p-hydroxybenzenesulfonate complex [Tm(C6H5O4S)2(H2O)6](C6H5O4S)·3H2O (1) was solvothermally synthesized and characterized by elemental analyses, photoluminescence, solid-state UV/vis diffuse reflectance, magnetic measurements and single-crystal X-ray diffraction. Complex 1 features an ionic structure with the thulium ion possessing a square antiprismatic geometry. Complex 1 crystallized in the monoclinic system with space group P21. Photoluminescent measurements with solid-state sample demonstrate that the anti-Stokes emission bands in the red/NIR spectral region 710 and 812 nm are observed from the Tm3+ 4f intrashell transitions from the 3F2,3 excited states to the 3H6 and 1G4 excited state to the 3H5 state, respectively. Solid-state UV/vis diffuse reflectance spectra of complex 1 show the existence of a wide optical band gap of 3.56 eV. Variable-temperature magnetic susceptibility and field dependence magnetization measurements are also studied and the magnetic susceptibility obeys the Curie-Weiss law (χ m =c/(T−θ)) with the value C being of 8.6 K and a negative Weiss constant θ being of −0.2 K.

Highly efficient 3d/4d-4f coordination polymer catalysts for carbon dioxide fixation into cyclic carbonates

Two novel highly efficient 3d/4d-4f one-dimensional (1D) double-chain coordination polymer catalysts with unique structures were synthesized for the first time. An X-ray single crystal structure analysis revealed that the two compounds are isomorphous and have a 1D metal-organic network coordination polymer structure. Both compounds also showed significant thermal stability and their structures remained stable up to 325 °C. The reaction conditions, type of substrate, amount of catalyst and its catalytic mechanism were investigated. The catalysts ([Dy2M2L4 (OAc)2 (MeOH)5 (H2O)]) (M = Zn, Cd) exhibited excellent catalytic activity in the cycloaddition of CO2 and styrene oxide (C8H8O, SO). High product yields, high selectivity, and the highest turnover frequency (TOF) of 28 400 h-1 were achieved. Additionally, the catalysts can significantly enhance the application of the present types of 3d/4d-4f catalysts in catalysis for transformations involving the fixation of CO2.

Ambient chemical fixation of CO2 using a highly efficient heterometallic helicate catalyst system

Two novel heptanuclear 3d–4f helicates have been synthesized and characterized.