LnIII Coordination Research Articles

Two Three-Dimensional LnIII Coordination Polymers Exhibiting Luminescent Sensing and a Magnetocaloric Effect.

Two lanthanide 3D coordination polymers [Ln2(L)4Cl2(H2O)4]n (Ln = Eu (1), Gd (2)) with quinoline-2-carboxylic acid (HL) as the ligand were successfully synthesized and characterized. Complex 1 exhibits a highly sensitive and selective luminescent response to 2,6-dipicolinic acid (DPA) in tap water and is virtually unaffected by interferences such as amino acids, aromatic carboxylic acids, and ions. With the addition of DPA, the luminescence intensity of complex 1 decreases rapidly to the naked eye. The detection limit of 1 toward DPA is 3.36 μM, which is much less than the infectious dose (60 μM) of the anthrax spores, indicating the high sensitivity of 1 to DPA. This study offers a basis for employing lanthanide complexes in real sample analysis, enabling direct and efficient detection of DPA with high sensitivity and specificity. Additionally, it is noteworthy that at a magnetic field strength of 7 T and a temperature of 3 K, the maximum entropy change for complex 2 attains a value of 23.56 J kg-1 K-1.

A new 3D HoIII-organic framework constructed from 1,3,5-tris(4-carboxyphenyl)benzene and 1,10-phenanthroline: Crystal structure, morphological and solid state luminescence properties

A new polynuclear LnIII coordination compound (1) with the stoichiometric formula {[Ho(BTB)(phen)]·(DMF)}n, (H3BTB ​= ​1,3,5-Tris(4-carboxyphenyl)benzene, phen ​= ​1,10 –phenanthroline monohydrate and DMF ​= ​N, N – dimethylformamide) has been synthesized by the solvothermal method and characterized by the infrared spectroscopy, thermogravimetric analysis, single-crystal X-ray diffraction studies, elemental analysis and solid-state electronic absorption properties and solid-state photoluminescence measurements. The XRD analyses indicate that 1 crystallizes in a monoclinic system with space group P21/c and also each HoIII ion has eight coordination, forming a distorted square antiprismatic geometry. For all the coordinated oxygen atoms, six of them belong to five carboxylate groups from different BTB3−ligands, while two nitrogen atoms from only one phen ligand were involved in the coordination. Two crystallographically equivalent HoIII ions are bridged to a dimeric unit as secondary unit buildings (SUBs) by four carboxyl groups in different directions, which also form typical 1D hexagonal channels with BTB3− ligands, these channels are connected in a three-dimensional (3D) framework. Also, these open channels were occupied by two different BTB3− ligands. According to the 3D Hirshfeld surface and 2D fingerprint plots analysis, H⋯H intermolecular interactions are the dominant interactions in the HoIII. Additionally, the π⋯π stacking information determined by the shape index and curvedness plots coincides with the crystal structure analysis. Moreover, photoluminescence properties of 1 were recorded and investigated at room temperature in the Vis-NIR region. Under the excitation of UV light, 1 exhibited strong yellowish-orange emission with CIE chromaticity coordinates (0.480, 0.430). 1 emits at 521, 575 and 653 ​nm correspond to 5F3 → 5I8, 5S2 +5F4→ 5I8 and 5F5→ 5I8 in the visible region, whereas only one weakly peak at 761 ​nm originated to 5S2 +5F4→ 5I7 in the NIR region. This polymeric complex can potentially be applied to luminescent probes or OLEDs.

Highly disordering nanoporous frameworks of lanthanide-dicarboxylates for catalysis of CO2 cycloaddition with epoxides

A series of nanoporous [LnIII4(di-nitro-BPDC)4(NO2)3(OH)(H2O)5]·n(methanol) (LnIII ​= ​PrIII, NdIII, SmIII, EuIII, GdIII, PrIII/GdIII and PrIII/EuIII; di-nitro-BPDC2- ​= ​2,2′-dinitrobiphenyl-4,4′-dicarboxylate) was synthesized and characterized. Founded on Lewis acidic LnIII possessing vacant coordination sites and functional groups of di-nitro-BPDC2-, their catalytic activities were evaluated based on the CO2 cycloaddition reactions with epoxides under ambient pressure and solvent-free conditions. Depending on catalytic conditions, satisfying turnover number and turnover frequency of 1106 and 276 h-1, respectively, could be yielded with ≥79(±4)% conversion and 87(±1)% selectivity. The correlation between the catalysis performance and structural factors is proposed on a basis of experimental and computation results. These include the restrained transportation even in the nanoporous framework and crystallographic disorder in the LnIII coordination environment. The excellent robustness of the catalysts, effects of lanthanide contraction, and synergistic activities of the heterometallic PrIII/GdIII and PrIII/EuIII catalysts are also included.

2D Lanthanide Coordination Polymers: Synthesis, Structure, Luminescent Properties, and Ratiometric Sensing Application in the Hydrostable PMMA-Doped Hybrid Films

Three LnIII coordination polymers, [LnL(NO3)3]n∙2C4H8O2 (LnL, Ln= Nd, NdL; Eu, EuL; Tb, TbL) based on a asymmetric poly-monodentate ligand L, which has abundant branched end groups for chelating Ln...

Effect of Heterocyclic Ring on LnIII Coordination, Luminescence and Extraction of Diamides of 2,2'-Bipyridyl-6,6'-Dicarboxylic Acid.

We have synthesized and examined several complexes of lanthanides with diamides of 2,2′-bipyridyl-6,6′-dicarboxylic acid bearing various hetaryl-based side chains for the elucidation of the effect of the heterocycle on the structure and properties of the ligands. The multigram scale methods for the preparation of various N-alkyl-hetaryls and their diamides were developed. The solid state structure of 6-methyl-2-pyridylamide of 2,2′-bipyridyl-6,6′-dicarboxylic acid possesses a flat structure where the conformation is completely different from that previously observed for N-alkylated 2,2′-bipyridyl-6,6′-dicarboxamides and 2,6-pyridinedicarboxamides. The complexes of new ligands were synthesized and NMR and X-Ray studied their structure in solution and solid state. The results demonstrate that complexes possess the same structures both in solid state and in solution. Stability constants of the complexes were less when comparing with dimethyl-substituted diamides, but higher than for unsubstituted dianilide. Contrarily, the extraction ability of 2-pyridyl-diamide is significantly lower than for corresponding anilide. Specific interaction of extractant with solvent molecules, which is not available for electron-sink pyridine amides, can explain this. The luminescence of new Eu complexes was significantly higher than for all previously 2,2′-bipyridyl-6,6′-dicarboxamides and QY reaches 18%. Asymmetry ratios of Eu complexes were 25% higher when compared other complexes with 2,2′-bipyridyl-6,6′-dicarboxamides, which indicates large deviation from the inversion center.

Mixed lanthanide coordination polymers for temperature sensing and enhanced NdIII NIR luminescence

Three LnIII coordination polymers, [Ln2L3(NO3)3]n·2CH3COOCH2CH3 (Ln = Nd (Nd2L3), Eu (Eu2L3), Tb (Tb2L3)), following coordination-assembly reactions involving a new bi-monodentate salicylamide ligand, L = 1,4-bis[(2΄-thenylaminoformyl)phenoxyl]methyl}-benzene, have been successfully synthesized. Among them, Nd2L3 and Tb2L3 were structurally authenticated by single-crystal X-ray diffraction and the results indicate both Nd2L3 and Tb2L3 are one-dimensional corrugated blockchains with LnIII containing 64-membered block loops filled by ethyl acetate molecules alternating in nearly orthogonal directions. For they are isomorphous, two binary co-doped lanthanide coordination polymers, Tb0.965Eu1.035L3 and Tb0.717Nd1.283L3 are obtained. Luminescent studies indicate that Tb0.965Eu1.035L3 exhibits a temperature recognition property with the significantly high sensitivity of 2.61% per K in the 296–386 K temperature range upon excitation at 345 nm as well as white emission when excited in the range of 370–390 nm. Tb0.717Nd1.283L3 shows enhanced NdIII-centred NIR luminescence and diminished TbIII-centred luminescence as compared to those of Nd2L3 and Tb2L3. The results presented herein show that the energy transfer from TbIII to both EuIII and NdIII has been successfully achieved in Tb0.965Eu1.035L3 and Tb0.717Nd1.283L3. Generally speaking, this work explores the potential applications of lanthanide-based coordination polymers based on multi-monodentate salicylamide ligand in the area of thermal sensing.

Three LnIII coordination compounds based on 1,1′,1″-(benzene-1,3,5-triyltris(methylene))tris(4-carboxypyridinium)tribromide: Synthesis, structures, and properties

An exploration of reactions of 1,1′,1″-(benzene-1,3,5-triyltris(methylene))tris(4-carboxypyridinium)-tribromide (H3LBr3) with LnIII salts has led to the formation of three complexes, {[LnL(H2O)2]·3(NO3)·6H2O} (Ln = Eu (1), Gd (2), and Tb (3)). Single-crystal X-ray analyses revealed that these complexes are isomorphous and have 3-D, channel-like structures, in which the carboxylic acids are fully deprotonated with syn–syn μ2-η1:η1 type bridging modes and L ligands in a chair-shaped configuration. Both 1 and 3 showed strong luminescence upon excitation. Magnetic measurements were performed for 2 and 3. The magnetic studies show that very weak antiferromagnetic couplings exist between GdIII and GdIII in 2. Moreover, powder X-ray diffraction, infrared spectroscopy, and elemental analysis were also performed.

Lanthanide coordination compounds with benzimidazole-based ligands. luminescence and EPR

LnIII coordination compounds were synthesized with two benzimidazolic ligands, 2 pb = 2-(2-pyridyl)benzimidazole and 4tb = 2-(4-thiazolyl)benzimidazole, with Eu, Gd, Tb and Dy, namely: [Ln (NO3)3 (Ln)2]⋅S, where Ln = 2 pb, 4tb and S = solvent. They were characterized by IR, 1D and 2D 1H and 13C NMR, solid state UV–Vis–NIR absorption and emission and EPR spectroscopies, X-ray powder diffraction, elemental analyses, electrical conductivity and magnetic susceptibility. The compounds of EuIII with 2 pb and 4tb, TbIII and DyIII with 4tb showed luminescence at RT in the solid state; their emission life time ranged from 0.026 to 1.82 ms. 2 pb and 4tb sensitized lanthanides luminescence. Results of DFT theoretical calculations for the ligand (H2L) are used to assign the ligand singlet and triplet excited state energy levels. Additionally, a full analysis of the X-band EPR spectra in the solid state gave the following results, at 297 K for [Gd(NO3)3 (2 pb)2]·CH3COCH3, g = 1.990, |D| = 0.0687 cm−1, E = 0.0165 cm−1 and λ = |E/D| = 0.240; for [Gd(NO3)3 (4tb)2]⋅CH3COCH3, g = 2.000; |D| = 0.0670 cm−1, E = 0.000 cm−1 and λ = |E/D| = 0.000. At lower temperature, 128 K, compounds showed an increase of the rhombicity as the temperature decreased.

Synthesis, Structure, and Magnetic Properties of a Family of Complexes Containing a {CoII2DyIII} Pivalate Core and a Pentanuclear CoII4DyIII Derivative

A series of new CoII–LnIII complexes with polynuclear {Co2Ln(NO3)(Piv)6} (Ln = La, Gd, Dy; Piv = pivalate) cores were prepared by self‐assembly reactions or step‐by‐step assembly. [Co2Dy(NO3)(Piv)6(MeCN)2] was used as the starting compound for the synthesis of the trinuclear analogue [Co2Dy(NO3)(Piv)6(py)2] (py = pyridine) and the pentanuclear complex [{Co2Dy(NO3)(Piv)6}{CoL(Piv)(H2O)}2][NO3]2 [L = 2,6‐bis(2‐pyridyl)‐4‐(4‐pyridyl)pyridine]. The effects of the coordination environment and temperature on the distortion of the LnIII coordination polyhedra were analyzed for a series of coordination compounds with MII2LnIII cores and close analogues. The distortion of the LnIII polyhedron depends on both the composition of the compound and the temperature; a temperature increase favors the D2d geometry of the LnIII coordination polyhedron. The magnetic properties of the complexes with CoII2DyIII cores were analyzed with consideration of the anisotropy of the CoII and DyIII ions. The compounds containing diamagnetic LaIII and isotropic GdIII ions, [Co2Ln(Piv)6(NO3)(MeCN)2] (Ln = La, Gd), which are isostructural to the CoIIDyIII analogue, were studied to evaluate the CoII magnetic‐anisotropy parameters to minimize the overparameterization of the magnetic properties in the fits for the Co2Dy systems. The magnetic properties of all complexes in this study are governed mainly by the magnetic properties of the isolated ions.

2D carboxylate-bridged LnIII coordination polymers: displaying slow magnetic relaxation and luminescence properties in the detection of Fe3+, Cr2O72- and nitrobenzene.

Eight new 2D isostructural lanthanide coordination polymers (Ln-CPs), [Ln(HL)(H2O)2(NO3)]·NO3 (1-Ln), Ln = NdIII, SmIII, EuIII, GdIII, TbIII, DyIII, HoIII, and YbIII ions, H2L = 4-(3,5-dicarboxylphenyl)-2-methylpyridine, were synthesized by using solvothermal methods and studied by structural analyses, magnetic analyses and luminescent probes. Crystallographic studies revealed that these compounds are 2D frameworks in which dinuclear units with double μ-syn,syn-carboxylate bridges are interlinked by single μ-trans,trans-carboxylate bridges from organic spacers. The layers are further stabilized and combined into 3D architectures through intra- and interlayer ππ stacking interactions and hydrogen bonding, respectively. Magnetic investigations indicated that the carboxylate bridges transmit intralayer antiferromagnetic coupling in 1-Nd, 1-Gd and 1-Ho but transmit intralayer ferromagnetic coupling in 1-Dy. Furthermore, 1-Dy also displays slow magnetic relaxation behavior with a high relaxation energy barrier (ΔUeff) of 100.7 K and a pre-exponential factor (τ0) of 1.4 × 10-8 s under zero dc field. The luminescence investigations showed that CPs 1-Eu and 1-Tb can serve as highly selective and recyclable sensing materials for Fe3+, Cr2O72- and nitrobenzene. Thus, both 1-Eu and 1-Tb should be excellent candidates for multifunctional sensors.

Periodic Behavior of Lanthanide Coordination within Reverse Micelles

Trends in lanthanide(III) (Ln(III)) coordination were investigated within nanoconfined solvation environments. Ln(III) ions were incorporated into the cores of reverse micelles (RMs) formed with malonamide amphiphiles in n-heptane by contact with aqueous phases containing nitrate and Ln(III); both insert into pre-organized RM units built up of DMDOHEMA (N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide) that are either relatively large and hydrated or small and dry, depending on whether the organic phase is acidic or neutral, respectively. Structural aspects of the Ln(III) complex formation and the RM morphology were obtained by use of XAS (X-ray absorption spectroscopy) and SAXS (small-angle X-ray scattering). The Ln(III) coordination environments were determined through use of L(3)-edge XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure), which provide metrical insights into the chemistry across the period. Hydration numbers for the Eu species were measured using TRLIFS (time-resolved laser-induced fluorescence spectroscopy). The picture that emerges from a system-wide perspective of the Ln-O interatomic distances and number of coordinating oxygen atoms for the extracted complexes of Ln(III) in the first half of the series (i.e., Nd, Eu) is that they are different from those in the second half of the series (i.e., Tb, Yb): the number of coordinating oxygen atoms decrease from 9O for early lanthanides to 8O for the late ones--a trend that is consistent with the effect of the lanthanide contraction. The environment within the RM, altered by either the presence or absence of acid, also had a pronounced influence on the nitrate coordination mode; for example, the larger, more hydrated, acidic RM core favors monodentate coordination, whereas the small, dry, neutral core favors bidentate coordination to Ln(III). These findings show that the coordination chemistry of lanthanides within nanoconfined environments is neither equivalent to the solid nor bulk solution behaviors. Herein we address atomic- and mesoscale phenomena in the under-explored field of lanthanide coordination and periodic behavior within RMs, providing a consilience of fundamental insights into the chemistry of growing importance in technologies as diverse as nanosynthesis and separations science.

Unusual Coordination Behaviour of a Phosphonate‐ and Pyridine‐Containing Ligand in a Stable Lanthanide Complex

AbstractAn experimental study of the coordination of lanthanide ions with {ethane‐1,2‐diylbis[imino(pyridin‐2‐ylmethanediyl)]}bis(phosphonic acid), a ligand containing phosphonate and pyridine arms attached to the well‐known ethylenediamine scaffold, is reported. The X‐ray crystal structure of an anionic, octacoordinate EuIII complex of the formula [C(NH2)]6[Eu2(L)2(CO3)2]·8H2O has been obtained and found to contain cyclic dimeric complex anions in which the coordination environment of each EuIII ion is composed of three oxygen atoms from phosphonate groups, two nitrogen atoms from imino groups and one nitrogen atom from a pyridine group, a combination that has seldom been observed for LnIII complexes. In order to check the coordination behaviour of the ligand, an investigation of the complexes in solution has been performed, which revealed a different coordination mode. The protonation constants of the free ligand and the stability constants of their complexes with selected lanthanide ions (LaIII, SmIII, EuIII, GdIII, TbIII, HoIII and LuIII) have been determined potentiometricaly at 25 °C and an ionic strength of 0.1 M (KCl). The results obtained show the formation of monomeric, protonated ([LnH2L], [LnHL]) and nonprotonated ([LnL]) species in the pH range studied (2–11). The determined stability constants (log βLnL) are relatively high, varying between 14.96 and 16.42. The EuIIIL system was also fully characterized by means of UV/Vis spectroscopy, which indicated that the coordination process starts above pH 3 and remains constant in the range pH 4–10. In contrast to the crystal structure, solution NMR and luminescence studies suggested that the pyridine moieties are not present in the LnIII coordination sphere. These results suggest that this ligand–unsaturated metal ion coordination sphere may provide a potential binding site for other target molecules.

Structure of the LnIII tris(β-diketonate) adduct with substituted bipyridine determined by the ESR and computer simulation data

The structural analog of liquid-crystalline adducts of lanthanides containing nitroxyl radicals in the bipyridine moiety was synthesized. The distances between the radicals in the ligand and adduct were determined by the pulse ESR technique. The obtained data were used as a criterion for the adequate choice of the parameters of the semiempirical quantum chemical calculation of the structures of the LnIII coordination compounds containing paramagnetic centers.

Novel lanthanide(III) coordination polymers with 1,4-bis(phenyl-sulfinyl)butane forming unique lamellar square array: syntheses, crystal structures, and properties.

The syntheses, characterization, structures, and properties of a series of LnIII coordination polymers with a flexible bis(sulfinyl) ligand, 1,4-bis(phenylsulfinyl)butane (L), are reported. Unique noninterpenetrated two-dimensional (4,4) nets are formed in these complexes. The coordination number of the LnIII ions across the whole LnIII series remains unchanged, and all the complexes of this series are isomorphous and isostructural. The perchlorate anions may set as a template in the formation of these unique square arrays, and the counteranions may be a key factor in controlling the structures of such complexes.