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β-Triketonates have been recently used as chelating ligands for lanthanoid ions, presenting unique structures varying from polynuclear assemblies to polymers. In an effort to overcome low solubility of the complexes of tribenzoylmethane, four β-triketones with higher lipophilicity were synthesised. Complexation reactions were performed for each of these molecules using different alkaline bases in alcoholic media. X-ray diffraction studies suggested that the ligands were undergoing decomposition under the reaction conditions. This is proposed to be caused by in situ retro-Claisen condensation reactions, consistent with two examples that have been reported previously. The lability of the lanthanoid cations in the presence of a varying set of potential ligands gave rise to structures where one, two, or three of the molecules involved in the retro-Claisen condensation reaction were linked to the lanthanoid centres. These results, along with measurements of ligand decomposition in the presence of base alone, suggest the solvent used will modulate the impact of the retro-Claisen condensation in these complexes. [ABSTRACT FROM AUTHOR]

This review aims to provide an overview of recent examples of lanthanoid-calixarene complexes incorporated into light-emitting materials. Background information on the antenna effect and early work on lanthanoid complexes on calixarenes is provided to set the context. Classes of materials discussed include polymers, nanoparticles, and metal clusters. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of 5,11,17,23-tetra- tert-butyl-25-hydroxy-26,27,28-tris(tetrazol-5-ylmethoxy)calix[4]arene is reported. Purification of the macrocycle required the use of preparative HPLC techniques. The macrocycle was found to be a poorer ligand for complexation of lanthanoid cations than the bis(tetrazole) analogue, but somewhat more effective than the tetrakis(tetrazole)-substituted derivative. Two metal complexes of the tris(tetrazole)-calixarene were structurally characterised. A polymeric sodium salt of the tris(tetrazole)-calixarene was isolated from a solution containing yttrium and a sodium acetate buffer. A praseodymium complex was isolated in the presence of an ammonium acetate buffer, where the calixarene acts as a unidentate ligand, bound to the metal atom through one tetrazole N-atom. Increasing the amount of buffer resulted in the crystallisation of a metal-free ammonium salt of the calixarene. [ABSTRACT FROM AUTHOR]

The preparation of discrete tetranuclear lanthanide/alkali metal (Ae) assemblies bearing a tribenzoylmethane ligand (LH) is discussed. These assemblies have the general formula [Ln(Ae·HOEt)(L)4]2, where Ln3+ = Gd3+, Tb3+, Dy3+, Ho3+and Ae+ = Na+, K+, Rb+. The coordination geometries of the lanthanide species were analyzed and compared, revealing a trend between an eight-coordinate square antiprism and triangular dodecahedron dependent on the nature of lanthanide, alkali metal, and lattice solvent. The potassium-containing analogs were also analyzed for their magnetic susceptibility. [ABSTRACT FROM AUTHOR]

Lanthanoid complexes of a tetra-amide substituted calix[4]arene in the cone conformation are characterised by single crystal X-ray structure determination. The structural analysis shows that the metal ions are coordinated to the calixarene through the eight O donor atoms, along with one aqua ligand which is located within the cavity of the calixarene. The calixarene ligand was covalently incorporated into a polymethylmethacrylate monolith throughp-allyl functional groups, followed by loading with a range of lanthanoid cations giving rise to light-emitting materials. The emission from the hydrid materials was found to be comparable to the solution phase emission. [ABSTRACT FROM AUTHOR]

The reaction of hydrated lanthanoid chlorides with tribenzoylmethane and an alkali metal hydroxide consistently resulted in the crystallization of neutral tetranuclear assemblies with the general formula [Ln(Ae ⋅HOEt)( L)4]2 (Ln=Eu3+, Er3+, Yb3+; Ae=Na+, K+, Rb+). Analysis of the crystal structures of these species revealed a coordination geometry that varied from a slightly distorted square antiprism to a slightly distorted triangular dodecahedron, with the specific geometrical shape being dependent on the degree of lattice solvation and identity of the alkali metal. The near-infrared (NIR)-emitting assemblies of Yb3+ and Er3+ showed remarkably efficient emission, characterized by significantly longer excited-state lifetimes ( τobs≈37-47 μs for Yb3+ and τobs≈4-6 μs for Er3+) when compared with the broader family of lanthanoid β-diketonate species, even in the case of perfluorination of the ligands. The Eu3+ assemblies show bright red emission and a luminescence performance ( τobs≈0.5 ms, ${{\Phi}{{{\rm L}\hfill \atop {\rm Ln}\hfill}}}$≈35-37 %, ηsens≈68-70 %) more akin to the β-diketonate species. The results highlight that the β-triketonate ligand offers a tunable and facile system for the preparation of efficient NIR emitters without the need for more complicated perfluorination or deuteration synthetic strategies. [ABSTRACT FROM AUTHOR]

Highlights • Polydentate tetrazole ligands form primary coordination sphere lanthanoid complexes. • Tetrazoles interact extensively with the second coordination sphere of lanthanoids. • Over one third of known lanthanoid tetrazole complexes reported since 2015. Abstract While tetrazole derivatives are well established as anionic ligands for d-block elements, there is a growing interest in lanthanoid complexes of these compounds. Diverse structural chemistry results from the presence of four potential donor N atoms, and the conjugated nature of the heterocycle can impact on the photophysical properties of the complexes. This review examines the range of structurally characterised lanthanoid–tetrazolato complexes, focussing on the structural features of the ligand that impact on the tendency to interact with the first or second coordination spheres. [ABSTRACT FROM AUTHOR]

Lanthanoid picrate (pic) complexes of 5,11,17,23-tetra- tert -butyl-25-hydroxy-26,27,28-tris(diethylcarbamoylmethoxy)calix[4]arene (L H) have been synthesised and structurally characterised, to complete this series for all lanthanoids (other than promethium). From cerium to lutetium, three structural types are observed: Type I, [Ln(L)(O,O ′-pic)](pic), Ln = Ce–Dy; Type II, [Ln(L)(O -pic)](pic), Ln = Tb, Ho; Type III, [Ln(L)(H O Et)](pic)2, Ln = Er–Lu. With lanthanum, three different ten-coordinate complexes were characterised; [Ln(L)(O,O ′-pic)(HOEt)](pic), [Ln(L)(O,O ′-pic)(OH2)](pic), and [Ln(L)(O,O ′-pic)(HOMe)](pic). The crystallisation of Type I and II observed for terbium shows that the stability of the different structures are sensitively poised at the transition points. Nevertheless, the structures show that the vacant space in the coordination sphere left by the trisamide L tends to reduce across the series as expected. It is occupied by a bidentate picrate anion and unidentate solvent molecule with lanthanum, a bidentate picrate anion for cerium to dysprosium (Type I), a unidentate picrate anion for terbium and holmium (Type II), and finally a unidentate solvent molecule from erbium to lutetium (Type III). The coordination number thus reduces from 10 to 8 across the series. Co-ligand binding in a sequence of calixarene complexes changes as a function of lanthanoid cation size. [ABSTRACT FROM AUTHOR]

Large metal—oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate coligand. The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate coligand structure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length. [ABSTRACT FROM AUTHOR]