Eu5(μ4-OH)(μ3-OH)4(μ-DBM)4(DBM)6 (DBM=dibenzoylmethide): a novel Eu5 square-pyramid polynuclear complex with a rare μ4-OH bridging mode

Lanthanide molecular cluster-aggregates as the next generation of optical materials

In this perspective, we provide an overview of the recent achievements in luminescent lanthanide-based molecular cluster-aggregates (MCAs) and illustrate why MCAs can be seen as the next generation of highly efficient optical materials. MCAs are high nuclearity compounds composed of rigid multinuclear metal cores encapsulated by organic ligands. The combination of high nuclearity and molecular structure makes MCAs an ideal class of compounds that can unify the properties of traditional nanoparticles and small molecules. By bridging the gap between both domains, MCAs intrinsically retain unique features with tremendous impacts on their optical properties. Although homometallic luminescent MCAs have been extensively studied since the late 1990s, it was only recently that heterometallic luminescent MCAs were pioneered as tunable luminescent materials. These heterometallic systems have shown tremendous impacts in areas such as anti-counterfeiting materials, luminescent thermometry, and molecular upconversion, thus representing a new generation of lanthanide-based optical materials.

A 12-Connected [Y4((μ3-OH)4]8+ Cluster-Based Luminescent Metal-Organic Framework for Selective Turn-on Detection of F- in H2O

Fluoride ion (F^-) is one of the most hazardous elements in potable water. Over intake of F^- can give rise to dental fluorosis, kidney failure, or DNA damage. As a result, developing affordable, equipment-free and credible approaches for F^- detection is an important task. In this work, a new three dimensional rare earth cluster-based metal-organic framework assembled from lanthanide Y(III) ion, and a linear multifunctional ligand 3-nitro-4,4'-biphenyldicarboxylic acid, formulated as {[Y(μ₃-OH)]₄[Y(μ₃-OH)(μ₂-H₂O)_0.25(H₂O)_0.5]₄[μ₄-nba]₈}_n (1), where H₂nba = 3-nitro-4,4'-biphenyldicarboxylic acid, has been hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that 1 crystallizes in tetragonal system with P4¯2₁m space group, and features a 3D framework with 1D square 18.07(3)² Ų channels running along the [0,0,1] or c-axis direction. The structure of 1 is built up of unusual eight-membered rings formed by two types of {Y₄O₄} clusters connected to each other via 12 μ₄-nba^2- and 4 μ₃-OH^- ligands. Three crystallographic independent Y³⁺ ions display two coordinated configurations with a seven-coordinated distorted monocapped trigonal-prism (YO₇) and an eight-coordinated approximately bicapped trigonal-prism (YO₈). 1 is further stabilized through O-H⋯O, O-H⋯N, C-H⋯O, and π⋯π interactions. Topologically, MOF 1 can be simplified as a 12-connected 2-nodal Au₄Ho topology with a Schläfli symbol {4²⁰·6²⁸·8¹⁸}{4³}₄ or a 6-connected uninodal pcu topology with a Schläfli symbol {4¹²·6³}. The fluorescent sensing application of 1 was investigated to cations and anions in H₂O. 1 exhibits good luminescence probing turn-on recognition ability toward F^- and with a limit detection concentration of F^- down to 14.2 μM in aqueous solution (K_ec = 11403 M^-1, R² = 0.99289, σ = 0.0539). The findings here provide a feasible detection platform of LnMOFs for highly sensitive discrimination of F^- in aqueous media.

Oxidation of europium with ammonium perfluorocarboxylates in liquid ammonia: pathways to europium(II) carboxylates and hexanuclear europium(III) fluoridocarboxylate complexes

The novel coordination polymer [Eu(O₂CCF₃)₂(dmf)₂]_∞ (1) (dmf = N,N-dimethylformamide) containing europium(II) and the two new compounds (NH₄)₂[Eu₆F₈(O₂CCF₃)₁₂(CF₃COOH)₆] (2) and (NH₄)₂[Eu₆F₈(O₂CC₂F₅)₁₂(C₂F₅COOH)₆]·8C₂F₅COOH (3), both based on hexanuclear europiate(III) complexes, were synthesized from precursors with a Eu²⁺ : Eu³⁺ ratio >1, obtained by reaction of europium metal with ammonium perfluorocarboxylates in liquid ammonia. In the crystal structure of 1 the europium(II) ions are bridged by carboxylate groups and N,N-dimethylformamide to form polymeric chains with Eu²⁺⋯Eu²⁺ distances of 408.39(13)-410.49(13) pm. The compound crystallizes in the triclinic space group P1̄ (Z = 2). To the best of our knowledge, this is the first example of a (solvated) perfluorocarboxylate containing a lanthanoid in a subvalent oxidation state. In the crystal structures of 2 and 3 the europium(III) ions are bridged by fluoride ions and carboxylate groups to form hexanuclear complex anions with an octahedral arrangement of the cations. The Eu³⁺⋯Eu³⁺ distances are in the range of 398.27(15)-400.93(15) pm in 2 and 395.37(4)-399.78(5) pm in 3, respectively. Both compounds crystallize in the monoclinic space group type P2₁/n (Z = 4) and are the first examples of octahedro-hexanuclear europium carboxylates for which fluoride is reported as a bridging ligand. In all compounds the oxidation state of europium was monitored via¹⁵¹Eu Mössbauer and photoluminescene spectroscopy.

A fresh look at the structural diversity of dibenzoylmethanide complexes of lanthanides

Synthetic methods for dibenzoylmethanide lanthanide complexes as well as heterolanthanide ones were systematized revealing several species.

New NIR-emissive tetranuclear Er(iii) complexes with 4-hydroxo-2,1,3-benzothiadiazolate and dibenzoylmethanide ligands: synthesis and characterization

Two new Er complexes were prepared and studied.

Novel lanthanide-based polymeric chains and corresponding ultrafast dynamics in solution

Two types of structurally related one-dimensional coordination polymers were prepared by reacting lanthanide trichloride hydrates [LnCl(3)·(H(2)O)(m)] with dibenzoylmethane (Ph(2)acacH) and a base. Using cesium carbonate (Cs(2)CO(3)) and praseodymium, neodymium, samarium, or dysprosium salts yielded [Cs{Ln(Ph(2)acac)(4)}](n) (Ln = Pr (1), Nd (2), Sm (3), Dy (4)) in considerable yields. Reaction of potassium tert-butoxide (KOtBu) and the neodymium salt [NdCl(3)·(H(2)O)(6)] with Ph(2)acacH resulted in [K{Nd(Ph(2)acac)(4)}](n) (5). All polymers exhibit a heterobimetallic backbone composed of alternating lanthanide and alkali metal atoms which are bridged by the Ph(2)acac ligands in a linear fashion. ESI-MS investigations on DMF solutions of 1-5 revealed a dissociation of all the five compounds upon dissolution, irrespective of the individual lanthanide and alkali metal present. Temporal profiles of changes in optical density were acquired performing pump/probe experiments with DMF solutions of 1-5 via femtosecond laser spectroscopy, highlighting a lanthanide-specific relaxation dynamic. The corresponding relaxation times ranging from seven picoseconds to a few hundred picoseconds are strongly dependent on the central lanthanide atom, indicating an intramolecular energy transfer from ligands to lanthanides. This interpretation also demands efficient intersystem crossing within one to two picoseconds from the S(1) to T(1) level of the ligands. Magnetic studies show that [Cs{Dy(Ph(2)acac)(4)}](n) (4) has slow relaxation of the magnetization arising from the single Dy(3+) ions and can be described as a single-ion single molecule magnet (SMM). Below 0.5 K, hysteresis loops of the magnetization are observed, which show weak single chain magnet (SCM) behavior.

Synthesis and structural characterization of cationic 5-hydroxy-1,3-diketonate stabilized dinuclear complexes and tetranuclear lanthanoid clusters

5-Hydroxy-1,3-diketonate ligands have been found to stabilize dimeric complexes and tetrameric lanthanoid clusters dependent on the degree of steric bulk provided by the presence or absence of a methoxy group. Treatment of (R/S,Z)-1'-hydroxy-3-(hydroxy(phenyl)methylene)bi(cyclopentan)-2-one (Hhpb) and the p-methoxyphenyl derivative (Hhmb) with [LnCl(2)(H(2)O)(6)]Cl yields clusters of composition [Ln(4)(Cl)(2)(O)(hpb)(6)]Cl(2) (Ln = Nd (1), Ho (2), Tb (3), and Er (4)) and [Ln(2)(hmb)(5)]Cl (Ln = La (5), Nd (6), Tb (7), Dy (8), and Er (9)). Single crystal X-ray analysis of the tetranuclear cluster has revealed the lanthanoid core to be in a tetrahedral arrangement around a central mu(4)-oxygen, bridged by symmetrical chlorides and shrouded in six bridging hpb ligands. The dimeric complexes are stabilized by three bridging and two terminal hmb ligands. In each instance, double or single cationic charges respectively are balanced by chloride anions.

Lanthanide hydroxide cubane clusters anchoring ferrocenes: model compounds for fixation of organometallic fragments on a lanthanide oxide surface

The reaction of the lanthanide trichloride hexahydrates [LnCl(3).6H(2)O] (Ln = Yb, Lu) with two equivalents of benzoylferrocenoylmethane resulted in the tetranuclear lanthanide hydroxo clusters [Ln(4)(mu(3)-OH)(4)(FcacacPh)(8)] (Ln = Yb (1), Lu (2); FcacacPh = benzoylferrocenoylmethanide). Compounds 1 and 2 are made up of a distorted tetranuclear lanthanide Ln(4)O(4) cubane core consisting of four mu(3)-oxygen atoms while the eight FcacacPh ligands build up the peripheral part of the cluster. These compounds contain the maximum number of ferrocene units anchored to any molecular metal-heteroatom framework reported so far and for which the X-ray structures are known.

Synthesis and Characterization of Two Novel Lanthanide Coordination Polymers with an Open Framework Based on an Unprecedented [Ln7(μ3-OH)8]13+ Cluster

Two novel heptanuclear lanthanide clusters of the dicubane-like type [Ln(7)(micro(3)-OH)(8)](13+) (Ln = Ho (1), Yb (2)) were obtained via hydrothermal reaction, and as building blocks, they were formally assembled into porous three-dimensional networks through the linkage of 1,4-naphthalenedicarboxylate (1,4-NDA), forming first examples of porous lanthanide polymers with 1,4-NDA, [Ln(7)(micro(3)-OH)(8)(1,4-NDA)(6)(OH)(0.5)(Ac)(0.5)(H(2)O)(7)].4H(2)O (Ln = Ho, Yb). The coordinating water molecules and lattice water molecules are enclathrated in the cavities.

Synthesis and structural characterization of nonanuclear lanthanide complexes

A series of nonanuclear lanthanide oxo-hydroxo complexes of the general formula [Ln(9)(mu(4)-O)(2)(mu(3)-OH)(8)(mu-BA)(8)(BA)(8)](-)[HN(CH(2)CH(3))(3)](+).(CH(3)OH)(2)(CHCl(3)) (BA = benzoylacetone; Ln = Sm, 1; Eu, 2; Gd, 3; Dy, 4; Er, 5) were prepared by the reaction of hydrous lanthanide trichlorides with benzoylacetone in the presence of triethylamine in methanol and recrystallized from chloroform/methanol (1:10) at room temperature. These five compounds are isomorphous. Crystal data for 1: cubic, Pn3n; T = 180 K; a = 33.8652(4) A; V = 38838.4(8) A(3); Z = 6; D(calcd) = 1.125 g cm(-)(3); R1 = 3.37%. Crystal data for 2: cubic, Pn3n; T = 180 K; a = 33.8252(8) A; V = 38700.9(16) A(3); Z = 6; D(calcd) = 1.133 g cm(-)(3); R1 = 4.97%. Crystal data for 3: cubic, Pn3n; T = 180 K; a = 33.7061(6) A; V = 38293.5(12) A(3); Z = 6; D(calcd) = 1.157 g cm(-)(3); R1 = 5.13%. Crystal data for 4: cubic, Pn3n; T = 180 K; a = 33.5900(7) A; V = 37899.2(14) A(3); Z = 6; D(calcd) = 1.182 g cm(-)(3); R1 = 4.03%. Crystal data for 5: cubic, Pn3n; T = 180 K; a = 33.5054(8) A; V = 37613.6(16) A(3); Z = 6; D(calcd) = 1.202 g cm(-)(3); R1 = 4.86%. The core of the anionic cluster comprises two vertex-sharing square-pyramidal [Ln(5)(mu(4)-O)(mu(3)-OH)(4)](9+) units. The compounds were characterized by elemental analysis, IR, fast atom bombardment mass spectra, thermogravimetry, and differential scanning calorimetry. The thermal analysis indicated that the nonanuclear species were stable up to 150 degrees C. Luminescence spectra of 2 and magnetic properties of 1-5 were also studied.