Ancillary ligand modulated stereoselective self-assembly of triple-stranded Eu(iii) helicate featuring circularly polarized luminescence

Subtle adjustments for constructing multi-nuclear luminescent lanthanide organic polyhedra with triazole-based chelates

Controlled self-assembly of predetermined multi-nuclear lanthanide organic polyhedra (LOPs) still presents a challenge, primarily due to the unpredictable coordination numbers and labile coordination geometries of lanthanide ions. In this study, through introducing triazole-based chelates to increase the chelating angle of C2-symmetric linear ligands and stabilize the coordination geometry of Eu(III) centers, M4L6-type (M = EuIII, L = ligand) tetrahedra were efficiently synthesized, especially a biphenyl-bridged ligand which is well known to form M2L3-type helicates. A series of LOPs were formed and characterized by high-resolution electrospray ionization time-of-flight mass spectroscopy (ESI-TOF-MS) and X-ray crystallography. Moreover, the europium complexes exhibit bright emission (luminescence quantum yield up to 42.4%) and circularly polarized luminescence properties (|glum| up to 4.5 × 10-2). This study provides a feasible strategy for constructing multi-nuclear luminescent LOPs towards potential applications.

Enhancing the Circularly Polarized Luminescence of Europium Coordination Polymers by Doping a Chromophore Ligand into Superhelices

Lanthanide-based molecular materials showing efficient circularly polarized luminescence (CPL) activity with a high quantum yield are attractive due to their potential applications in data storage, optical sensors, and 3D displays. Herein we present an innovative method to achieve enhanced CPL activity and a high quantum yield by doping a chromophore ligand into a coordination polymer superhelix. A series of homochiral europium(III) phosphonates with a helical morphology were prepared with the molecular formula S-, R-[Eu(cyampH)3-3n(nempH)3n]·3H2O (S/R-Eu-n, n = 0-5%). The doping of chromophore ligand S- or R-nempH2 into superhelices of S/R-Eu-0% not only turned on the CPL activity with the dissymmetry factor |glum| on the order of 10-3 but also increased the quantum yield by about 14-fold. This work may shed light on the development of efficient CPL-active lanthanide-based coordination polymers for applications.

Helical fluxionality: numerical frustration drives concerted low-barrier screw motions of a tricopper cluster

Uneven allocation of resources creates frustration, tension, and conflicts. Confronted with an apparent mismatch between the number of donor atoms and the number of metal atoms to be supported, helically twisted ligands cleverly come up with a sustainable symbiotic solution. As an example, we present a tricopper metallohelicate exhibiting screw motions for intramolecular site exchange. A combination of X-ray crystallographic and solution NMR spectroscopic studies revealed thermo-neutral site exchange of three metal centres hopping back and forth inside the helical cavity lined by a spiral staircase-like arrangement of ligand donor atoms. This hitherto unknown helical fluxionality is a superimposition of translational and rotational movements of molecular actuation, taking the shortest path with an extraordinarily low energy barrier without compromising the overall structural integrity of the metal-ligand assembly.

Heterometallic Molecular Architectures Based on Fluorinated β-Diketone Ligands

This review summarizes the data on the synthesis of coordination compounds containing two or more different metal ions based on fluorinated β-diketonates. Heterometallic systems are of high interest in terms of their potential use in catalysis, medicine and diagnostics, as well as in the development of effective sensor devices and functional materials. Having a rich history in coordination chemistry, fluorinated β-diketones are well-known ligands generating a wide variety of heterometallic complexes. In this context, we focused on both the synthetic approaches to β-dicarbonyl ligands with additional coordination centers and their possible transformations in complexation reactions. The review describes bi- and polynuclear structures in which β-diketones are the key building blocks in the formation of a heterometallic framework, including the examples of both homo- and heteroleptic complexes.

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.

Asymmetric induction in quadruple-stranded europium(III) helicates and circularly polarized luminescence

Chiral supramolecular lanthanide-helicates are regarded as promising chiroptical materials due to their combination of ground and excited state chirality and special luminescence property from Ln3+, named as circularly polarized luminescence...