Lanthanide Clusters Research Articles

A lanthanide(iii) dodecanuclear structure with a acylhydrazone Schiff-base ligand: slow magnetic relaxation and magnetocaloric effects

In the complex synthesis process, the design of new type structures of lanthanide clusters with high nuclearity provides an opportunity to understand the nature of magnetic dynamics.

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

A series of novel asymmetry 3d-4f helicates Zn3LnL4 (H2L = N-(2-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)ethyl)-2-hydroxybenzamide, Ln = Dy(1), Gd(2), Er(3)) were successfully constructed via selective incorporation of groups with different coordination capabilities. These helicates with the well-defined conformation demonstrate high catalytic efficiency in converting CO2 to cyclic carbonates under mild conditions. Particularly, Zn3ErL4 showed superior catalytic performance with high catalytic activity (TOF up to 38 000 h-1) and extraordinary selectivity (up to 99%) across the wide substrate scope. Meanwhile, these 3d-4f helicates showed stable catalytic performance without being influenced by the moisture and air. The results presented herein highlight an important consideration for constructing heterometallic and asymmetric complexes for catalyzing CO2 conversion.

Two hexanuclear lanthanide Ln6III clusters featuring remarkable magnetocaloric effect and slow magnetic relaxation behavior

Two novel hexanuclear lanthanide clusters (1 and 2) were successfully prepared. Magnetic investigations reveal that 1 exhibits remarkable magnetocaloric effect and 2 displays interesting slow magnetic relaxation behaviors.

PH-controlled construction of lanthanide clusters from lacunary polyoxometalate with single-molecule magnet behavior

Six lanthanide clusters were synthesized via pH-controlled strategy: Na18[Ln4(Sb3O2)2(SbW10O37)2(SbW8O31)2(H2O)6]·(H2O)60 [Ln = Dy3+ (1), Ho3+ (2), Er3+ (3)] in pH 5.5 NaAc-HAc buffer solution displaying tetrameric architectures, and Na23[Ln3(SbW9O33)3(CH3COO)3(WO4)(H2O)3]·(H2O)50 [Ln = Dy3+ (4), Ho3+ (5), Er3+ (6)] in pH 7.2 NaAc/HAc solution featuring trimeric aggregates. Obviously, pH-controlled strategy can design the structures of lanthanide clusters. Moreover, the ac magnetic susceptibilities proved that compounds 1 and 4 manifested apparent slow magnetic relaxation behaviors. Interestingly, compound 1 exhibited both temperature- and frequency-dependent in-phase (χ′) and out-of-phase (χ″) ac signals, behaving as a zero-field SMM with Ueff = 46.8 K, τ0 = 8.11 × 10−7 s calculated on the basis of Orbach process, and Ueff = 58.2 K, τ0 = 3.63 × 10−7 s according to Raman and Orbach relaxation processes. Compound 4 was found to be a SMM with a fast QTM, yielding a reversal barrier Ueff = 1.12 K with τ0 = 9.27 × 10−6 s.

Lanthanide Doped Complexes and Organometallic Clusters: Design Strategies and their Applications in Biology and Photonics

In this review, we discuss the rational design of a new class of lanthanide-doped organometallic nanostructured materials called `molecular minerals`. Molecular minerals are nanostructured materials with a ceramic core made from chalcogenide groups and other heavy metals. Part of the central core atoms is replaced by suitable lanthanide atoms to impart fluorescent spectral properties. The ceramic core is surrounded by various types of organic networks thus making the structure partly ceramic and organic. The central core has superior optical properties and the surrounding organic ligand makes it easy to dissolve several kinds of organic solvents and fluoropolymers to make several kinds of active and passive photonic devices. This chapter starts with elaborate design strategies of lanthanidebased near-infrared emitting materials followed by the experimental results of selected near-infrared emitting lanthanide clusters. Finally, their potential applications in telecommunication, light-emitting diodes and medical imaging are discussed.

Exceptionally Complex Electronic Structures of Lanthanide Oxides and Small Molecules.

Lanthanide (Ln) oxide clusters and molecular systems provide a bottom-up look at the electronic structures of the bulk materials because of close parallels in the patterns of Ln 4fN subshell occupancy between the molecular and bulk Ln2O3 size limits. At the same time, these clusters and molecules offer a challenge to the theory community to find appropriate and robust treatments for the 4fN patterns across the Ln series. Anion photoelectron (PE) spectroscopy provides a powerful experimental tool for studying these systems, mapping the energies of the ground and low-lying excited states of the neutral relative to the initial anion state, providing spectroscopic patterns that reflect the Ln 4fN occupancy. In this Account, we review our anion PE spectroscopic and computational studies on a range of small lanthanide molecules and cluster species. The PE spectra of LnO- (Ln = Ce, Pr, Sm, Eu) diatomic molecules show spectroscopic signatures associated with detachment of an electron from what can be described as a diffuse Ln 6s-like orbital. While the spectra of all four diatomics share this common transition, the fine structure in the transition becomes more complex with increasing 4f occupancy. This effect reflects increased coupling between the electrons occupying the corelike 4f and diffuse 6s orbitals with increasing N. Understanding the PE spectra of these diatomics sets the stage for interpreting the spectra of polyatomic molecular and cluster species. In general, the results confirm that the partial 4fN subshell occupancy is largely preserved between molecular and bulk oxides and borides. However, they also suggest that surfaces and edges of bulk materials may support a low-energy, diffuse Ln 6s band, in contrast to bulk interiors, in which the 6s band is destabilized relative to the 5d band. We also identify cases in which the molecular Ln centers have 4fN+1 occupancy rather than bulklike 4fN, which results in weaker Ln-O bonding. Specifically, Sm centers in mixed Ce-Sm oxides or in SmxOy- (y ≤ x) clusters have this higher 4fN+1 occupancy. The PE spectra of these particular species exhibit a striking increase in the relative intensities of excited-state transitions with decreasing photon energy (resulting in lower photoelectron kinetic energy). This is opposite of what is expected on the basis of the threshold laws that govern photodetachment. We relate this phenomenon to strong electron-neutral interactions unique to these complex electronic structures. The time scale of the interaction, which shakes up the electronic configuration of the neutral, increases with decreasing electron momentum. From a computational standpoint, we point out that special care must be taken when considering Ln cluster and molecular systems toward the center of the Ln series (e.g., Sm, Eu), where treatment of electrons explicitly or using an effective core potential can yield conflicting results on competing subshell occupancies. However, despite the complex electronic structures associated with partially filled 4fN subshells, we demonstrate that inexpensive and tractable calculations yield useful qualitative insight into the general electronic structural features.

A New Three‐dimensional Metal‐organic Framework based on Dinuclear Rare Earth Cluster and Olsalazine

A new microporous metal organic frameworks Eu2(olz)3·7(DMF), based on olsalazine, has been successfully designed and synthesized. Eu‐olz has three‐dimensional structure with dinuclear rare earth cluster and drug molecule olsalazine as ligand, and features as low toxic MOF materials. The Eu‐olz exhibits weak fluorescent emission which can be ascribed to the luminescence of the organic ligand.

Influence of the para ‐Substituent in Lanthanoid Complexes of Bis‐Tetrazole‐Substituted Calix[4]arenes

5,11,17,23-Tetra-tert-butyl-25,27-dihydroxy-26,28-bis(tetrazole-5-ylmethoxy)calix[4]arene has been reported to form remarkable Ln19 and Ln12 elongated clusters, upon addition of aqueous ammonium carboxylates. The impact of the para substituent on lanthanoid cluster formation has been studied by synthesising two new bis-tetrazole calixarenes, with p-H, and p-allyl substituents. Solution phase dynamic light scattering measurements of the reaction mixtures indicated that clusters are not formed with the p-H and p-allyl derivatives, in contrast with the behaviour of the tert-butyl analogue. Lanthanoid complexes of the p-H and p-allyl calixarenes were characterised by single-crystal X-ray diffraction, and were found to form mononuclear complexes, linked to form a one-dimensional coordination polymer for the p-allyl system. All of the complexes were isolated as ammonium salts, with ammonium cation included in the calixarene cavity in most cases. It is concluded that the nature of the para substituent has a profound impact on the lanthanoid cluster formation process, and derivatives with more subtle structural changes will be required to determine if additional lanthanoid “bottlebrush” clusters can be isolated.

Lanthanides based metal organic frameworks for luminescence sensing of toxic metal ions

Two set of lanthanides-based metal organic framework structures incorporating 2,6-naphthalenedicarboxylic acids and 1,5 dihydroxy-2,6-naphthalenedicarboxylic have been successfully synthesized and fully characterized. Interestingly, when 1,5 dihydroxy-2,6-naphthalenedicarboxylic was employed as organic linker, the hydroxyl groups were not involved in the coordination to the lanthanide clusters and therefore hydroxyl-functionalized lanthanides MOFs (AUBM-3) were obtained. The photophysical properties of both set of MOFs were studied and their sensing properties for toxic elements Pb(II), Cr(III), As(III), Cd(II), and Hg(II) and for paraquat were investigated. The hydroxyl-functionalized structures have shown to be promising luminescent sensory materials with high selectivity and sensitivity to mercury.

A series of new polynuclear lanthanide(III) clusters prepared in alkylol amine

A series of new polynuclear lanthanide(III) clusters [Ln4(heda)6(Hheda)2Cl2]Cl4 [Ln = Sm (1a), Eu (1b), Hheda = N-(2-Hydroxyethyl)ethylenediamine] and [Ln6(heda)10(µ-OH)2]Cl6·2H2O [Ln = Y (2a), Gd (2b), Dy(2c), Tb(2d), Ho (2e), Er (2f), Tm(2g)] were solvothermally synthesized and structurally characterized. 1a-b consist of tetra-nuclear lanthanide(III) cluster [Ln4(heda)6(Hheda)2Cl2] built up from two unsaturated [Ln2(heda)3(Hheda)Cl]2+ complex cations via two bridging O atoms of two L− ligands. 2a-g are isostructural and contain hexa-nuclear lanthanide(III) clusters [Ln6(heda)10(µ-OH)2]6+ constructed by the linkages of two unsaturated trinuclear [Ln3(heda)5(µ-OH)] clusters, free Cl− anions as counterions and H2O molecules. Although many transition metal complexes were obtained by using HL ligand as chelating ligand, its polynuclear lanthanide(III) clusters have not been documented to date. 1a-b and 2a-g offer the only examples of polynuclear lanthanide(III) clusters of HL ligand. A preliminary investigation of nine polynuclear lanthanide(III) clusters reveals that the well-known lanthanide contraction has a significant influence on the formation of polynuclear lanthanide(III) clusters under solvothermal conditions. The luminescent properties of 1b and 2d were discussed, and magnetic properties of 1a and 2e were also investigated.

Rare-Earth and Antimony-Oxo Clusters Simultaneously Connecting Antimonotungstates Comprising Divacant and Tetravacant Keggin Fragments.

Four novel rare-earth (RE) and Sb-oxo clusters simultaneously bridging antimonotungstates (ATs) [H2N(CH3)2]8Na6H8{[RE4(H2O)6Sb6O4](SbW10O37)2(SbW8O31)2}·24H2O [RE = Dy3+ (1), Er3+ (2), Y3+ (3), Ho3+ (4)] were triumphantly isolated by using Na9[B-α-SbW9O33]·19.5H2O, dimethylamine hydrochloride, SbCl3, and RE(NO3)3·6H2O in acidic aqueous solution. Their tetrameric polyoxoanions are all established by two [SbW10O37]11- and two [B-α-SbW8O31]11- segments encapsulating a RE-Sb heterometal [RE4(H2O)6Sb6O4]22+ cluster. Under the O→W LMCT excitation at 268 nm of AT segments, RE ions in 1 and 2 can absorb the 3T1u→1A1g emission energy of AT segments, giving rise to the sensitization of AT segments to the emission of RE ions. Through the sensitization of AT segments, the emission intensities of RE ions in 1 and 2 are increased and lifetimes are prolonged. Photoluminescence and energy transfer measurements indicate that Dy3+ ions in 1 can obtain more energy from AT segments than to Er3+ ions in 2. Furthermore, the sensitization effects of AT segments to different f-f transitions of RE ions have been compared in 1 and 2. Under the sensitization of AT segments, the 4F9/2→6H15/2 transition obtains the most energy compared with the 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions in 1, and the 2H11/2→4I15/2 transition obtains more energy than the 4S3/2→4I15/2 transition in 2. It seems that the better energy level match of 3T1u→1A1g transition of AT segments with f-f emission transitions of RE ions will lead to a stronger sensitization effect.

Step-by-Step and Competitive Assembly of Two Dy(III) Single-Molecule Magnets with Their Performance Tuned by Schiff Base Ligands

The assembly process of lanthanide clusters often involves various complex assembly methods. Hence, studying the stepwise assembly mechanism is extremely difficult. In the assembly process of lanthanide clusters, if the in situ reaction or competitive reaction is involved, the reaction intermediates undergo rapid and complex changes, which makes research on the assembly mechanism even more difficult. Herein, 1-methyl-1H-benzo[d]imidazole-2-carbaldehyde (La) and 1-aminonaphthalen-2-ol (Lb) undergo a stepwise assembly reaction with Dy(III) salts under the promotion of a in situ Schiff base reaction to achieve Dy2 synthesis. The stepwise assembly mechanism is La + Lb → HL1 → Dy1 → Dy2. In the above Dy2 formation reaction, La is changed to 2-hydroxy-3-methoxybenzaldehyde (Lc), and then pyridin-2-ylmethanamine (Ld) is added. We have found that two different Schiff base ligands are formed in situ, and both are coordinated with Dy(III) ions to form a mixed ligand cluster Dy4 by competitive and stepwise assembly....

The stability, electronic, and magnetic properties of rare-earth doped silicon-based clusters.

The rare-earth doped silicon-based clusters exhibit remarkable structural, physical, and chemical properties, which make them attractive candidates as building units in designing of cluster-based materials with special optical, electronic, and magnetic properties. The structural, stability, electronic, and magnetic properties of pure silicon Sin +1 (n= 1-9) and rare-earth doped clusters SinEu (n= 1-9) are investigated using the "stochastic kicking" (SK) global search technique combined with density functional theory (DFT) calculations. It was found that: 1) the ground state structures of pure silicon clusters tend to form compact structures rather than cages with the increase of cluster size; 2) the ground state structures for doped species were found to be additional or substitutional sites, and the rare-earth atoms tend to locate on the surface of the silicon clusters; 3) the average binding energy of the doped clusters increased gradually and exhibited the final phenomenon of saturation with the increase of clusters size. The average binding energy of doped clusters was slightly higher than that of pure silicon clusters of the same size, which indicated that the rare-earth atom encapsulated by silicon enhanced the stability of the silicon clusters to some degree; 4) the doped clusters have strong total magnetic moments, which mainly originated from the contribution of rare-earth atoms, whereas the contribution of silicon atoms were almost negligible. As the cluster size increased, the total magnetic moments of binary mixed clusters tended to be stable.

Copper(I)-Based Highly Emissive All-Inorganic Rare-Earth Halide Clusters

Summary The development of new environmentally friendly luminescent materials is crucial for future solid-state lighting, sensor, and display applications. Here, a Cu(I)-based all-inorganic rare-earth halide material, Rb 8 CuSc 3 Cl 18 , has been synthesized by a solid-state reaction method. In this compound, two Cu(I) ions are connected to three rare-earth halide octahedra to form a paddle-wheel-like cluster. The Cu(I) coordinated rare-earth halide clusters contribute to a strong blue photoluminescence emission. This Cu(I)-regulated emission can be extended to other isostructural compounds, such as Rb 8 CuY 3 Cl 18 . Moreover, the crucial role of Cu(I) has been illustrated by the isostructural non-emissive Rb 8 AgSc 3 Cl 18 . On the basis of comprehensive spectroscopy studies and density functional theory calculations, we found that Cu(I) photo-oxidation and correct orbital-energy-level alignment are crucial for the observed bright-blue emission through a proposed metal (Cu)-to-octahedra ([ScCl 6 ] 3− ) charge-transfer mechanism. The discovery of Cu(I)-based all-inorganic rare-earth halide clusters establishes a new strategy for constructing promising emissive halide materials.

Tracking the Stepwise Formation of the Dysprosium Cluster (Dy10) with Multiple Relaxation Behavior.

High-nuclear lanthanide clusters are generally formed by the rapid accumulation of simple building units. Thus, tracking and observing the stepwise assembly process, which is vital for understanding the assembly mechanism, are extremely difficult. Herein, the decanuclear nanocluster [Dy10(L1)6(μ5-NO3)2(OAc)10(HOAc)2]·8H2O (Dy10, H3L1 = (E)-3-((3-ethoxy-2-hydroxybenzylidene)amino)propane-1,2-diol) was obtained from the reaction of Dy(NO3)3·6H2O, Dy(OAc)3·6H2O, 3-ethoxy-2-hydroxybenzaldehyde (L2), and 3-amino-1,2-propanediol (L3). The reaction process was further tracked by time-dependent high-resolution electrospray ionization mass spectrometry, and seven reaction intermediate fragments were screened. A stepwise assembly mechanism was observed based on these fragments, that is, L → Dy1 → Dy2 → Dy3 → Dy4 → Dy5 → Dy6 → Dy10. This study is the first to discover a stepwise assembly mechanism during the formation of high-nuclear lanthanide clusters (cluster nucleus > 3). Magnetic studies have shown the multiple relaxation behavior of Dy10.

A Giant Dy76 Cluster: A Fused Bi-Nanopillar Structural Model for Lanthanide Clusters.

Although great achievements have been made in the synthesis of giant lanthanide clusters, novel structural models are still scarce. Herein, we report a giant lanthanide cluster Dy76 , constructed from [Dy3 (μ3 -OH)4 ] and [Dy5 (μ4 -O)(μ3 -OH)8 ] building blocks. As the largest known Dy cluster, the structure of Dy76 can be seen as arising from the fusion of two Dy48 clusters; these clusters can be isolated under various synthetic conditions and were characterized by single-crystal X-ray diffraction. This new, fused structural model of the pillar motif has not been found in Ln clusters. Furthermore, the successful conversion of Dy76 back into Dy48 in a retrosynthetic manner supports the proposed fusion formation mechanism of Dy76 . Electrospray ionization mass spectrometry (ESI-MS) analysis suggests that the metal cluster skeleton of Dy76 shows good stability in various solvents. This work not only reveals a new structural type of Ln clusters but also provides insight into the novel fusion assembly process.

A Giant Dy76 Cluster: A Fused Bi‐Nanopillar Structural Model for Lanthanide Clusters

AbstractAlthough great achievements have been made in the synthesis of giant lanthanide clusters, novel structural models are still scarce. Herein, we report a giant lanthanide cluster Dy76, constructed from [Dy3(μ3‐OH)4] and [Dy5(μ4‐O)(μ3‐OH)8] building blocks. As the largest known Dy cluster, the structure of Dy76 can be seen as arising from the fusion of two Dy48 clusters; these clusters can be isolated under various synthetic conditions and were characterized by single‐crystal X‐ray diffraction. This new, fused structural model of the pillar motif has not been found in Ln clusters. Furthermore, the successful conversion of Dy76 back into Dy48 in a retrosynthetic manner supports the proposed fusion formation mechanism of Dy76. Electrospray ionization mass spectrometry (ESI‐MS) analysis suggests that the metal cluster skeleton of Dy76 shows good stability in various solvents. This work not only reveals a new structural type of Ln clusters but also provides insight into the novel fusion assembly process.

Two novel hydroxide anions bridged lanthanide coordination polymers based on fluorinated carboxylate ligand: Structures, luminescence and magnetic property

Two unique lanthanide coordination polymers, namely, {[Ln2(μ3-OH)2(Tfpht)2 (H2O)2·0.5bipy]}n (Ln = Gd (1) and Eu (2), H2Tfpht = 3,4,5,6-Tetrafluorophthalic acid, bipy = 4,4′-bipyridine) have been afforded successfully. The coordination polymers 1 and 2 are isostructural and have the same phase, both crystallizing in the triclinic system, with space group of P−1. They both exhibit one-dimensional (1-D) ribbon-double chains composed of trinuclear lanthanide clusters bridged by μ3-hydroxyl bridges and carboxyl oxygen atoms of Tfpht2− ligands, and the chains are further linked by hydrogen bonding interactions to give rise to a 2-D corrugated layer. The solid state luminescence emission spectra of coordination polymer 1 is based on the H2Tfpht acid ligand, whereas 2 displays the characteristic f-f transitions of Eu(III) ions. The direct-current (dc) magnetic susceptibility studies reveal the weak ferromagnetic interaction between the Gd(III) ions in coordination polymer 1.

Two dinuclear lanthanide(III) clusters (Gd2 and Dy2) constructed by bis-(o-vanillin) schiff base ligand exhibiting fascinating magnetic behaviors

Two new dinuclear lanthanide complexes, namely, [Ln2L(dbm)4]·2CH3OH (Ln = Gd (1) and Dy (2), H2L = N,N′-bis(3-methoxysalicylidene)-1,3-diamino-2-propanol, Hdbm = 1,3-diphenyl-1,3-propanedione) have been synthesized and characterized by elemental analyses, single crystal X-ray diffraction and magnetic measurements. The studies of single crystal X-ray diffraction analysis demonstrate that both 1 and 2 are isostructural with a [Ln2] core. Magnetic investigations reveal the presence of a weak antiferromagnetic interaction in 1 and 2, respectively, of which 1 displays magnetocaloric effect with a large magnetic entropy change (−ΔSm = 18.95(2) J kg−1 K−1 for ΔH = 7 T at 2 K), while 2 exhibits slow relaxation of magnetization with the anisotropy energy barrier ΔE/kB = 0.73(1) K.

Unique influence of rare earth (Pr, Nd, and Er) oxide surface acidic texture over CeO2/γ-Al2O3 catalysts for selective production of styrene using CO2 flow

Variety of rare earth oxide-doped CeO2/γ-Al2O3 catalysts were prepared by a wet impregnation method and evaluated for oxidative dehydrogenation of ethylbenzene (EB) using CO2 as soft oxidant in vapor-phase atmospheric-pressure conditions. Amongst the bare CeO2/γ-Al2O3 catalysts, 15 wt% CeO2/γ-Al2O3 exhibited excellent catalytic activity with noteworthy EB conversion and styrene selectivity. After incorporation of 3 wt% Er2O3, Pr2O3, or Nd2O3 oxide onto the 15 wt% CeO2/γ-Al2O3 (15CA) catalyst, unusual catalytic properties were observed in terms of formation of active solid-solution species. The greater fraction of CO2 molecule activation and dissociation phenomenon on the surface rare earth-doped CeO2/γ-Al2O3 catalysts compared with the bare CeO2/γ-Al2O3 catalyst were investigated. Among the rare earth-doped catalysts, 3ErCA showed superior mobile oxygen storage capacity and high CO2 utilization ability, along with optimal surface acidic properties compared with the rare earth solid-solution properties of (CexRE1−xO2−δ) Pr2O3 and Nd2O3 species. Moreover, the better catalytic activity of Er2O3 species can be explained on the basis of active metal–support synergistic interactions and noticeable surface acidic nature. All the catalysts were characterized by X-ray diffraction analysis, Brunauer–Emmett–Teller (BET) surface area measurements, H2-temperature programmed reduction, ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy, temperature-programmed desorption (NH3-TPD), scanning electron microscopy (SEM), and CO2 and O2 pulse chemisorption techniques to elucidate the metal oxide composition and influence of rare earth clusters such as Pr2O3, Nd2O3, and Er2O3 oxides on the catalytic activity.