Tetranuclear Lanthanide Research Articles

Self-assembly of tetra nuclear lanthanide (Pr, Nd) hydroxo clusters with functionalized β-diketone: Experimental and theoretical studies

Reaction of LnCl3·6H2O (Ln = Pr, Nd) with functionalized β-Diketone {ortho-hydroxydibenzoylmethane (HO-DBM)} in 1:2 ratio in methanol and in presence of triethylamine (excess) as base yielded two tetra nuclear lanthanide hydroxo clusters of composition [Ln4(O-DBM)4(HO-DBM)4(µ3-OH)2][Et3NH]2.3CH2Cl2, (Ln = Pr (1), Nd (2)). The clusters 1 and 2 has been structurally characterized by single crystal X-ray diffraction. A one-dimensional supramolecular chain is observed in the solid state structure (2), where dichloromethane solvent molecules are linked to the phenyl rings of adjacent diketone linkers through CH⋯π and Cl⋯π interactions. Theoretical studies support the stability of structure (2), with calculated geometric parameters aligning with experimental findings.

The self-assembly of tetranuclear [Gd4] cluster: Magnetic refrigeration and efficient CO2 chemical fixation

In this paper, the self-assembly of Gd3+ ions and ligand 5-chlorine-8-hydroxylquinoline (HL) successfully generated one tetranuclear lanthanide compound [Gd4(µ3-OH)2(L)6(acac)4] (1) (L = 5-chlorine-8-hydroxylquinoline; Hacac = acetylacetone), in which four Gd3+ ions are connected into a [Gd4O2] cluster. Magnetic studies revealed that anti-ferromagnetic interactions between neighbouring Gd3+ ions were observed in 1. In addition, 1 also shows magnetocaloric effect and the −ΔSm value reaches 28.05 J kg−1 K−1 at T = 2.0 K and ΔH = 7 T. Catalytic experiments indicated that 1 and tetra-n-butylammonium bromide (TBAB) could synergistically catalyze the cycloaddition reaction of CO2 and epoxides at relatively mild condition.

Structural determinations of homo and heterodi- or tetra-nuclear lanthanide complexes and their characterization by μ-Squid experiments

Two families of homo- and heterodinuclear complexes are prepared and structurally characterized, thus demonstrating that genuine complexes involving two lanthanide ions closely located in the lanthanide series can be obtained, taking into account a simple rule that necessitates introduction of the better Lewis acid Ln ion (the smallest Ln ion) into the inner coordination site of the main ligand used in this synthesis. In the first family, the presence of a deprotonated orthovanillin ligand (ovan) around the Ln ion positioned in the outer coordination site of the main ligand allows a good isolation of the dinuclear complexes. These complexes behave as SMSs when a Dy ion is coordinated in the outer site but a weak magnetic magnetic Ln-Dy interaction is needed to create a weak magnetic field able to suppress collapsing of the hysteresis loops in zero external applied field at very low temperature. In the second family, the ovan ligand is replaced by a chloride ligand, so that two dinuclear units are linked together by two Cl…HOMe hydrogen bonds to yield tetranuclear complexes that are not SMMs. Eventually these two preparation pathways are expected to give novel and genuine examples of homo or hetero-dinuclear and tetranuclear lanthanide complexes likely to furnish in future coordination complexes useful in quantum computing.

Syntheses of new di-nuclear and tetra-nuclear lanthanide 9-anthracenecarboxylates: Magnetocaloric effect, slow magnetic relaxation and luminescent properties

Lanthanide complex-based materials with magnetic and luminescent properties have received a great deal of attention, owing to their importantly potential applications in diverse fields. In this work, the 9-anthracenecarboxylic acid (9-Haca) as bridging ligand was applied in combination with optically active π-conjugated 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) to construct a series of new di-nuclear and tetra-nuclear lanthanide 9-anthracenecarboxylates [La2(9-aca)6(tptz)2(μ-H2O)]·0.25H2O (1), [Ln2(9-aca)6(tptz)2(H2O)2]·0.5AQ·CH3COOH2H2O [Ln = Sm (2a), Eu (2b), Gd (2c), Tb (2d), Dy (2e), Tm (2f); AQ = 9,10-anthracenedione] and [Ln4(9-aca)10(tptz)2(CH3COO)2]·H2O [Ln = Eu (3a), Gd (3b), Dy (3c)]. 1 displays a di-nuclear centrosymmetric moiety [La2(9-aca)6(tptz)2(μ-H2O)] built up from two complex [La(9-aca)2(tptz)] groups bridged by one H2O molecule and two syn-syn-μ2-η1:η1-9-aca‒ bridging ligands, while 2a‒2f are isostructural and comprise another di-nuclear centrosymmetric moieties [Ln2(9-aca)6(tptz)2(H2O)2] based on two complex [Ln(9-aca)2(tptz)(H2O)] groups connected by two syn-syn-μ2-η1:η1-9-aca– bridging ligands. 3a‒3c are isostructural and show tetra-nuclear centrosymmetric moieties [Ln4(9-aca)10(tptz)2(CH3COO)2] containing three types of coordination modes of 9-aca– ligands. The present compounds offer the only examples of lanthanide 9-anthracenecarboxylates decorated by optically active tptz. Magnetic investigations of 2a, 2c‒2f, and 3b‒3c indicate that 3c is typical of slow relaxation of the magnetization, while 2c and 3b show significant magnetocaloric effect (MCE) with the value of –ΔSm of 5.26 J/(kg·K) at 4 K and 15.65 J/(kg·K) at 2 K (ΔH = 7 T), respectively. The luminescent properties were also studied and reveal that the characteristic luminescent properties of the π-conjugated aromatic ligands are introduced into magnetic lanthanide 9-anthracenecarboxylates, simultaneously exhibiting slow magnetic relaxation (or MCE) and luminescent properties.

Solid state structures and solution behaviour of tetranuclear lanthanide(III) carbonate-bridged coordination compounds of chiral 3 + 3 amine macrocycle.

The linking of two dinuclear macrocyclic units of large triphenolic hexaazamine by two carbonate anions results in the formation of dimeric tetranuclear Sm(III), Eu(III) and Gd(III) complexes. These complexes were initially obtained serendipitously by fixation of atmospheric carbon dioxide and subsequently obtained in a rational way by the application of carbonate salts. The X-ray crystal structures of these isomorphic complexes show highly folded conformation of the macrocycle. This type of conformation is also confirmed by 2D NMR spectra of the Sm(III) complex. The ESI-MS and NMR spectra reveal also that these carbonate complexes exist in solution in two different forms that are in a concentration-dependent dynamic equilibrium.

Tetranuclear lanthanide complexes display significant slow magnetic relaxation with an open hysteresis loop and the magnetocaloric effect

Herein, we report two tetranuclear lanthanide complexes, of which the Dy4-complex exhibits significant single-molecule magnetic properties with the open hysteresis loop is detected until 6.5 K and a coercive field of 453 Oe is observed at 1.8 K.

Assembly of tetra-nuclear lanthanide compounds: Structures, magnetic refrigeration and slow relaxation of magnetization

Two novel tetranuclear lanthanide compounds with the formula [Ln4(L1)2(L2)2(μ2- OCH3)2(CH3OH)2]·CH3OH (Ln = Gd (1), Dy (2), H2L1 = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-8-hydroxyquinoline, H3L2 = 2-[(2-(N'-acetylhydrazino)propanehydrazide)methyl]-8-hydroxyquinoline) were successfully prepared, and structurally and magnetically characterized. Crystal structural analyses reveal that two compounds are isostructural and they all consist of a tetranuclear Ln4 cluster. All Ln(III) ions in them are eight-coordinated and located in a distorted triangular dodecahedron geometry. Magnetic studies indicate that 1 exhibits large magnetocaloric effect with the entropy change (-ΔSm) of 32.10 J Kg−1 K−1 (at T = 2.0 K and ΔH = 7 T), and 2 displays slow magnetic relaxation behaviors.

Di- and Tetranuclear Dysprosium Single-Molecule Magnets Bridged by Unprecedentedly Disassembled Nitrogen-Enriched Tetrazine Derivatives

A series of di- and tetranuclear lanthanide complexes with the formulas [Dy2bmzch(tmhd)5 (CH3OH)]·CH3OH (1), [Dy2bmzch(dbm)4 (CH3O)(CH3OH)]·0.5CH3OH·0.5H2O (2), and Dy4bmzch(btfa)10 (3), where tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate, dbm = dibenzoylmethane, btfa = benzoyltrifluoroacetone, and bmzch = (Z)-N-[(E)-pyrimidin-2-ylmethylene]pyrimidine-2-carbohydrazonate, were structurally and magnetically characterized. More strikingly, although the nitrogen-enriched bridged ligand 3,6-di(pyrimidin-2-yl)-1,2,4,5-tetrazine (bmtz) was initially adopted, the structures of the complexes obtained indicated that bmtz underwent unprecedented asymmetric ring opening and generated a new ligand bmzch. Combined with different β-diketonates, di- and tetranuclear dysprosium complexes were constructed in which the structural patterns are very sensitive to the selected β-diketonates. In view of this, the bilateral and unilateral dinuclear Dy2 complexes 1 and 2 and tetranuclear Dy4 complex 3 were obtained by choosing different β-diketonates. Magnetic test results reveal that both complexes 1 and 3 showcase typical slow magnetic relaxation behavior without an external direct-current field and the effective energy barrier of the latter is almost twice that of the former, while complex 2 only displays in-field single-molecule-magnetic behavior. Also of note is that these are the first tetrazine-type dysprosium-based single-molecule-magnets undergoing in situ asymmetric ring-opening reaction of this ligand that are formed.

Quick and robust PDF data acquisition using a laboratory single-crystal X-ray diffractometer for study of polynuclear lanthanide complexes in solid form and in solution

Self-assembled polynuclear lanthanide hydroxo complexes are important objects in the reticular chemistry approach to the design of various functional materials. Revealing their structure in the solid state and understanding the molecular mechanism of self-assembly in solution require a universal and reliable structural method. Pair distribution function (PDF) analysis is a powerful technique which enables structural insight for a wide range of crystalline and amorphous materials on the nanoscale, but commonly measurements are performed at synchrotron X-ray sources or on specially designed laboratory diffractometers. In the present paper, a standard Bruker D8 QUEST single-crystal X-ray diffractometer equipped with a micro-focus Mo tube and CMOS Photon III detector was adapted to measure PDF data of high quality with Q max = 16.97 Å–1 for solid and liquid samples. An improved data collection strategy and the original data reduction software FormagiX enable calibration and azimuthal full-frame integration of 2D frames, delivering reliable PDFs up to 80 Å with instrumental parameters Q damp = 0.018 Å−1 and Q broad = 0.010 Å−1. The effectiveness of the developed approach was demonstrated with reference samples and real-case studies of tetranuclear lanthanide hydroxocarboxylates in solid form and in solution.

A series of tetranuclear rare-earth complexes and two-step slow magnetic relaxation in Dy4 complex

A series of new tetranuclear lanthanide metal complexes of [Ln4(μ4-O2−)(HL)2(L)2]·0.5(H2NCH2CHOHCH2NH2)·(CH3CN)·1.25(H2O) (Ln = Tb(1)), [Ln4(μ4-O2−)(HL)2(L)2]·0.5(H2NCH2CHOHCH2NH2)·0.5(CH3CN)·0.25(H2O) (Ln = Dy(2) or Ho(3)), were elaborately synthesized using a Schiff base ligand, 1,3-bis(5-bromosalicylideneamino)-2-propanol) (H3L). They were structurally and magnetically characterized. The crystallographic data reveal the tetranuclear lanthanide core of complexes 1–3 bridged by one μ4-O2− ion. Complexes 1–3 contained one unusual Ln4 boat-shaped unit, forming a novel Ln4 cluster. Detailed static and dynamic magnetic analysis of complexes 1–3 revealed single-molecule magnet (SMM) behavior with anisotropy barrier of Ueff = 20.98 K and Ueff = 43.47 K and two pre-exponential factors τ0 = 7.66 × 10−7 s and τ0 = 9.75 × 10−7 s for complex 2.

Magnetocaloric effect and slow magnetic relaxation in peroxide-assisted tetranuclear lanthanide assemblies

Investigation of a series of rare peroxide-assisted tetranuclear lanthanide assemblies revealed both significant magnetocaloric effect and slow magnetic relaxation.

Magnetic investigation in di- and tetranuclear lanthanide complexes

Dinuclear and tetranuclear dysprosium-based complexes have been constructed by using a crab-like hydrazone ligand, with the former acting as a typical single-molecule magnet and the later showing diamagnetic ground state.

Single molecule magnet behavior and magnetic refrigeration of carbonyl oxygen-bridged tetranuclear lanthanide complexes

Three lanthanide complexes were fabricated and characterized. 1 exhibited cryogenic magnetic refrigeration property and 3 displayed slow relaxation of the magnetization.

Asymmetric Ring Opening in a Tetrazine-Based Ligand Affords a Tetranuclear Opto-Magnetic Ytterbium Complex.

We report the formation of a tetranuclear lanthanide cluster, [Yb4 (bpzch)2 (fod)10 ] (1), which occurs from a serendipitous ring opening of the functionalised tetrazine bridging ligand, bpztz (3,6-dipyrazin-2-yl-1,2,4,5-tetrazine) upon reacting with Yb(fod)3 (fod- =6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octandionate). Compound 1 was structurally elucidated via single-crystal X-ray crystallography and subsequently magnetically and spectroscopically characterised to analyse its magnetisation dynamics and its luminescence behaviour. Computational studies validate the observed MJ energy levels attained by spectroscopy and provides a clearer picture of the slow relaxation of the magnetisation dynamics and relaxation pathways. These studies demonstrate that 1 acts as a single-molecule magnet (SMM) under an applied magnetic field in which the relaxation occurs via a combination of Raman, direct, and quantum tunnelling processes, a behaviour further rationalised analysing the luminescent properties. This marks the first lanthanide-containing molecule that forms by means of an asymmetric tetrazine decomposition.

Tetranuclear Lanthanide Complexes Supported by Hydroxyquinoline‐Calix[4]arene‐Ligands: Synthesis, Structure, and Magnetic Properties of [Ln4(H3L)2(µ‐OH)2(NO3)4] (Ln = Tb, Dy, Yb) and [Dy2(H4L)2(NO3)](NO3)

The coordination behavior of the calixarene‐based N4O4 donor ligand H6L bearing two pendant 8‐hydroxyquinoline‐2‐hydrazone arms towards the lanthanide ions Tb3+, Dy3+, and Yb3+ has been investigated. H6L was found to support tetra‐ and dinuclear mixed‐ligand complexes with the pendant hydrazone units in a deprotonated enolate and/or a neutral amide form. The direct reaction of H6L with Ln(NO3)3(H2O)6 and NEt3 in a 1:1:2 molar ratio leads to tetranuclear [Ln4(H3L)2(µ‐OH)2(η2‐NO3)4] complexes {Ln = Tb (1), Dy (2), Yb (3)} containing a rectangular arrangement of four eight‐coordinate Ln3+ ions bridged by two hydroxido‐ and four quinolinolato‐O atoms as established by X‐ray crystallography. Degradation of 2 occurs upon addition of further equiv. of H6L to give dinuclear [Dy2(H4L)(NO3)2(MeCN)2]NO3 (4) with eight‐ and ten‐coordinated Dy3+ ions. ESI‐MS studies reveal that such dinuclear species exist also in the solution state. The results of variable temperature direct and alternating current magnetic susceptibility measurements for 1–4 and high frequency EPR study on 4 are also reported.

Synthesis of two lanthanide clusters LnIII4 (Gd4 and Dy4) with [2 × 2] square grid shape: Magnetocaloric effect and slow magnetic relaxation behaviors

Two isostructural tetranuclear lanthanide clusters named [Ln4(L)4(CH3O)4]·CH3OH (Ln = Gd(III) for 1, Dy(III) for 2, H2L = N′-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl) picolinohydrazide) were successfully isolated by using a polydentate Schiff based ligand and Ln(III) nitrate salts. The structures of 1 and 2 were characterized by X-ray structural analyses, they are held by four double deprotonated ligands L2−. In them all the lanthanide ions are eight-coordinated and distributed over four vertices of a parallelogram, presenting a Ln4 cluster with a strict [2 × 2] square grid pattern. The details of magnetic analysis show that 1 displays weak anti-ferromagnetic exchange between neighboring Gd(III) ions through carboxylate oxygen and methanol oxygen ligand atoms. Furthermore, 1 exhibits significant magnetocaloric effect with the maximum entropy change –ΔSm value of 28.5 J/(kg·K) for ΔH = 7.0 T at 2.0 K. For compound 2, remarkable slow magnetic relaxation behaviors are observed in the presence of zero magnetic field with τ0 = 1.02 × 10−6 s and energy barrier ΔE/kB = 43.24 K.

Synthesis, Structures, and Magnetic Properties of Zigzag Tetranuclear Lanthanide Complexes

Five isostructural tetranuclear lanthanide complexes with the general formula [Ln4(teaH2)2(teaH)2(NO3)6]·2CH3OH [Ln3+ = Dy3+ (1), Tb3+ (2), Ho3+ (3), Er3+ (4), and Gd3+ (5)] were successfully synthesized by the reaction of various lanthanide nitrate and triethanolamine (teaH3) ligand. Single crystal X‐ray analyses reveal the eight‐coordinate Ln3+ centers adopt a slightly distorted triangular dodecahedron geometry and nine‐coordinate Ln3+ ions own an approximately capped square antiprism environment in similar zigzag Ln4 core. Magnetic studies demonstrate the presence of anitferromagnetic interactions between Ln3+ centers without obvious SMM behavior.

Lanthanide 5,7-Disulfonate-1,4-naphthalenedicarboxylate Frameworks Constructed from Trinuclear and Tetranuclear Lanthanide Carboxylate Clusters: Proton Conduction and Selective Fluorescent Sensing of Fe3.

The novel sulfonate-carboxylate ligand of 5,7-disulfonate-1,4-naphthalenedicarboxylic acid (H4-DSNPDC) was synthesized, and its series of lanthanide compounds {[Ln3(μ2-OH)(DSNPDC)2(H2O)x]·yH2O}n (JXNU-7; Ln = La3+, x = 10. y = 4; Ln = Nd3+, Sm3+ Eu3+, x = 9, y = 2) and {[Ln4(μ3-OH)4(DSNPDC)2(H2O)11]·28H2O}n (JXNU-8; Ln = Eu3+, Gd3+) are presented. JXNU-7 is a three-dimensional structure based on linear trinuclear Ln3 building units, while JXNU-8 has a two-dimensional layer constructed from tetranuclear Ln4(μ3-OH)4 building units. The representative Eu compounds of JXNU-7 and -8 show good proton conductive properties under high humidity. The hydrophilic sulfonate groups pointing to the pores and the water molecules included in the pores mainly contribute to the high proton conductivity for the materials. The presence of one-dimensional infinite hydrogen-bonded networks in channels of JXNU-7(Eu) facilitates a fast and efficient proton transfer, resulting in higher proton conductivity in comparison to that of JXNU-8(Eu). Additionally, JXNU-7(Eu) with a characteristic red emission exhibits a promising potential for selective sensing of Fe3+ ions in aqueous solution. Our work demonstrates the integration of functional organic components (sulfonate groups) and inorganic components (lanthanide centers) in MOFs for the successful preparation of multifunctional MOF materials.

Designing Multicoordinating Nitronyl Nitroxide Radical Toward Multinuclear Lanthanide Aggregates.

Profiting from a multicoordinating nitronyl nitroxide radical, i.e. a functionalized nitronyl nitroxide biradical ligand, a family of novel tetranuclear lanthanide complexes, formulated as [RE4(hfac)12(NITPhO-3Pybis)2] (RE = Gd 1, Tb 2, Dy 3, Ho 4, and Y 5; NITPhO-3Pybis = 5-(3-pyridinyloxy)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene; hfac = hexafluoroacetylacetonate) were successfully constructed and characterized. In these complexes, the designed functionalized nitronyl nitroxide biradical ligand functions as the chelating and/or bridging ligand to bind the lanthanide ions, resulting in tetranuclear octa-spin lanthanide complexes with a circle-shaped arrangement. Direct-current magnetic data show that antiferromagnetic interaction dominates in the Gd derivative, while ferromagnetic coupling plays a leading role in complex Y, in which the relevant magnetic exchange parameters were obtained through applicable magnetic models. Dynamic magnetic studies of Tb and Dy analogues exhibit apparent frequency-dependent out-of-phase signals, which are typical features for slow magnetic relaxation behavior. The values of Ueff and τ0 were obtained as follows: Ueff = 10.5 K and τ0 = 6.6 × 10-7 s for the Tb complex and Ueff = 5.2 K and τ0 = 2.5 × 10-6 s for the Dy compound. Intriguingly, the butterfly shaped hysteresis loop is found for the Tb analogue. Guided by fluorescence spectra, the representative peaks are identified for the Tb derivative.

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.