Antiprismatic Coordination Geometry Research Articles

Structures, photoluminescence, and magnetism of 1D lanthanide coordination polymers dominated on 3,5‐dichlorobenzoate

AbstractTwo series of novel coordination polymers (CPs), namely, Ln3(3,5‐DCB)9(bipy) (H2O)2·(bipy) [Ln = Nd (1), Sm (2)] and Ln2(3,5‐DCB)6(bipy)H2O [Ln = Eu (3), Gd (4), Tb (5) and Dy (6)], have been synthesized by hydrothermal reaction of a bridging ligand, 3,5‐dichlorobenzoic acid (3,5‐HDCB), with LnCl3·nH2O and N‐donor neutral ligand, 2,2′‐bipyridine (bipy). Single‐crystal x‐ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), and powder x‐ray diffraction (PXRD) for 1–6 are presented. CPs 1 and 2 exhibit trinuclear lanthanide architectures, in which the center Ln(III) are seven‐coordinated and eight‐coordinated adopting monocapped triangular prismatic, distorted square antiprism and bicapped trigonal prismatic coordination geometry, respectively, whereas CPs 3–6 are isostructural dinuclear structures. The center Ln(III) ions are also seven‐coordinated and eight‐coordinated with different coordinate modes adopting distorted monocapped triangular prismatic and square antiprism coordination geometry. Trinuclear CPs 1 and 2 are packed together via hydrogen‐bonding interaction to form the two‐dimensional (2D) supramolecular layers. CPs 3–6 exhibit 2D layers by the π–π interaction. CPs 2, 3, 5, and 6 display the characteristic fluorescent emissions of Sm(III), Eu(III), Tb(III), and Dy(III), respectively. CPs 1 and 4–6 exhibit corresponding weak anti‐ferromagnetic and ferromagnetic interactions of Nd(III), Gd(III), Tb(III), and Dy(III) in the low‐temperature range.

Decoration of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) with N-oxides increases the T1 relaxivity of Gd-complexes.

High complex stability and longitudinal relaxivity of Gd-based contrast agents are important requirements for magnetic resonance imaging (MRI) because they ensure patient safety and contribute to measurement sensitivity. Charged and zwitterionic Gd3+-complexes of the well-known chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) provide an excellent basis for the development of safe and sensitive contrast agents. In this report, we describe the synthesis of DOTA-NOx, a DOTA derivative with four N-oxide functionalities via "click" functionalization of the tetraazide DOTAZA. The resulting complexes Gd-DOTA-NOx and Eu-DOTA-NOx are stable compounds in aqueous solution. NMR-spectroscopic characterization revealed a high excess of the twisted square antiprismatic (TSAP) coordination geometry over square antiprismatic (SAP). The longitudinal relaxivity of Gd-DOTA-NOx was found to be r1=7.7 mm-1 s-1 (1.41 T, 37 °C), an unusually high value for DOTA complexes of comparable weight. We attribute this high relaxivity to the steric influence and an ordering effect on outer sphere water molecules surrounding the complex generated by the strongly hydrated N-oxide groups. Moreover, Gd-DOTA-NOx was found to be stable against transchelation with high excess of EDTA (200 eq) over a period of 36 h, and it has a similar in vitro cell toxicity as clinically used DOTA-based GBCAs.

Highly selective recovery of yttrium from mining wastewater using biosynthetic iron sulfide nanoparticles

The selective recovery of rare earth elements (REEs) from mining wastewater has become a hot research topic due to the increasing industrial value of REEs. Herein, biosynthetic iron sulfide nanoparticles (nFeS) were deployed as a superior adsorbent to selectively recover Y(Ⅲ) from mining wastewater. The maximum adsorption efficiency achieved for of Y(Ⅲ) by nFeS was 81.2 % compared to only 38.7 % for Eu(Ⅲ) and 20.8 % for Mn(Ⅱ), demonstrating that nFeS had a high selective adsorption for Y(Ⅲ). To understand the origins of the high selectivity of nFeS, the removal of REEs by the capping layer and the FeS-core were separately investigated. Specifically, given the hard and soft acid base principle (HASB) and the square antiprism coordination geometry of Y(Ⅲ), the adsorption of Y(Ⅲ) by the capping layer was predominantly attributed to CO and –NH2 serving as a monodentate ligand to strongly chelate with Y(Ⅲ), while Y(Ⅲ) interacted with Fe–O on the FeS-core and –COOH more via ion-exchange with Y(Ⅲ). Collectively, cooperative interactions between the capping layer and FeS-core resulted in the overall highly selective adsorption of Y(Ⅲ) by nFeS, suggest this approach has significant potential for future practical remediation and recovery applications to Y(Ⅲ) rich mining wastewaters.

Synthesis and properties of [NR4]3[SbS4] (R = Me, Et, n-Pr, n-Bu) and the crystal structures of [N(n-Bu)4]3[SbS4]⋅6H2O and [N(n-Bu)4]3[Sb(S2O3)3]·2THF

The tetra-alkylammonium tetrathioantimonate(V) salts, [NR4]3[SbS4] (R = Me, Et, n-Pr, n-Bu), have been prepared in basic solution from aqueous [NR4]OH, sulfur and Sb2S3, and characterised by microanalysis, IR, Raman, 1H and 121Sb NMR spectroscopy. The crystal structure of [N(n-Bu)4]3[SbS4]·6H2O shows the presence of the tetrahedral [SbS4]3− anion (disordered over two sites), and also connected through an H-bonding network with the lattice water molecules. The alkylammonium salts are soluble in water and, with the exception of [NMe4]3[SbS4], are also soluble in weakly polar organic solvents, including halocarbons and MeCN. Solubility increases with the R group Me < Et < n-Pr < n-Bu, making the [N(n-Bu)4)3[SbS4] a convenient reagent to explore coordination chemistry or materials applications for which water as the solvent is not suitable. [N(n-Bu)4]3[Sb(S2O3)3]·2THF, the first thiosulfate complex of a p-block element, was produced by slow decomposition of [N(n-Bu)4]3[SbS4] in THF solution in the presence of the [NH(n-Bu)3]Cl (as a source of H+), confirming the instability of the [SbS4]3− anion in acidic media, and the crystal structure of [N(n-Bu)4]3[Sb(S2O3)3]·2THF shows a trigonal antiprismatic coordination geometry with a S3O3 donor set at the antimony(III) centre in the anion.

Slow magnetic relaxation behavior of a {Dy2} complex based on a large π-conjugated bridging ligand

Binuclear lanthanide single molecule magnets (Ln-SMMs) based on large π-conjugated bridging ligands have shown potential in achieving excellent SMM performance. However, their members are still scarce until now. In this work, a novel binuclear Ln-SMM featuring a large π-conjugated bridging ligand, [Dy2(hfac)6(tpphz)]·CH2Cl2 (1), has been prepared. Its two DyIII centers are chelated and bridged by the large π-conjugated tetrapyrido[3,2-a:2′,3′-c:3′′,2′′-h:2′′′,3′′′-j]phenazine (tpphz) ligand. Three 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac-) ions acting as terminal ligands further complete the square antiprism coordination geometry of each DyIII center. Magnetic measurements revealed that 1 exhibits zero field SMM behavior with a single magnetic relaxation process. The effective energy barrier (Ueff) is 13.79 K. Interestingly, dual relaxation behavior including well-separated slow relaxation (SR) and fast relaxation (FR) processes was further observed when a dc field was applied. It could be ascribed to the different single ion anisotropy of the DyIII centers, as well as a possible contribution of magnetic interactions in the system of 1. The Ueff values for the SR and FR processes are 27.3 and 1.30 K, respectively.

Facile transmetallation of [SbIII(DOTA)]- renders it unsuitable for medical applications.

The antimony(iii) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) has been prepared and its exceptionally low stability observed. The Sb(iii) ion in Na[Sb(DOTA)]·4H2O shows an approximately square antiprismatic coordination geometry that is close to superimposable to the Bi(iii) geometry in [Bi(DOTA)]− in two phases containing this anion, Na[Bi(DOTA)]·4H2O, [H3O][Bi(DOTA)]·H2O for which structures are also described. Interestingly, DOTA itself in [(H6DOTA)]Cl2·4H2O·DMSO shows the same orientation of the N4O4 metal binding cavity reflecting the limited flexibility of DOTA in an octadentate coordination mode. In 8-coordinate complexes it can however accommodate M(iii) ions with rion spanning a relatively wide range from 87 pm (Sc(iii)) to 117 pm (Bi(iii)). The larger Bi3+ ion appears to be the best metal–ligand size match since [Bi(DOTA)]− is associated with greater complex stability. In the solution state, [Sb(DOTA)]− is extremely susceptible to transmetallation by trivalent ions (Sc(iii), Y(iii), Bi(iii)) and, significantly, even by biologically important divalent metal ions (Mg(ii), Ca(ii), Zn(ii)). In all cases just one equivalent is enough to displace most of the Sb(iii). [Sb(DOTA)]− is resistant to hydrolysis; however, since biologically more abundant metal ions easily substitute the antimony, DOTA complexes will not be suitable for deployment for the delivery of the, so far unexploited, theranostic isotope pair 119Sb and 117Sb.

Electronic Structure of Ytterbium(III) Solvates-a Combined Spectroscopic and Theoretical Study.

The wide range of optical and magnetic properties of lanthanide(III) ions is associated with their intricate electronic structures which, in contrast to lighter elements, is characterized by strong relativistic effects and spin-orbit coupling. Nevertheless, computational methods are now capable of describing the ladder of electronic energy levels of the simpler trivalent lanthanide ions, as well as the lowest energy term of most of the series. The electronic energy levels result from electron configurations that are first split by spin-orbit coupling into groups of energy levels denoted by the corresponding Russell-Saunders terms. Each of these groups are then split by the ligand field into the actual electronic energy levels known as microstates or sometimes mJ levels. The ligand-field splitting directly informs on the coordination geometry and is a valuable tool for determining the structure and thus correlating the structure and properties of metal complexes in solution. The issue with lanthanide complexes is that the determination of complex structures from ligand-field splitting remains a very challenging task. In this paper, the optical spectra-absorption, luminescence excitation, and luminescence emission-of ytterbium(III) solvates were recorded in water, methanol, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF). The electronic energy levels, that is, the microstates, were resolved experimentally. Subsequently, density functional theory calculations were used to model the structures of the solvates, and ab initio relativistic complete active space self-consistent field calculations (CASSCF) were employed to obtain the microstates of the possible structures of each solvate. By comparing the experimental and theoretical data, it was possible to determine both the coordination number and solution structure of each solvate. In water, methanol, and N,N-dimethylformamide, the solvates were found to be eight-coordinated and have a square antiprismatic coordination geometry. In DMSO, the speciation was found to be more complicated. The robust methodology developed for comparing experimental spectra and computational results allows the solution structures of homoleptic lanthanide complexes to be determined.

Excited State Properties of Lanthanide(III) Complexes with a Nonadentate Bispidine Ligand.

EuIII, TbIII, GdIII and YbIII complexes of the nonadentate bispidine derivative L2 (bispidine=3,7‐diazabicyclo[3.3.1]nonane) were successfully synthesized and their emission properties studied. The X‐ray crystallography reveals full encapsulation by the nonadentate ligand L2 that enforces to all LnIII cations a common highly symmetrical capped square antiprismatic (CSAPR) coordination geometry (pseudo C4v symmetry). The well‐resolved identical emission spectra in solid state and in solution confirm equal structures in both media. As therefore expected, this results in long‐lived excited states and high emission quantum yields ([EuIIIL2]+, H2O, 298 K, τ=1.51 ms, ϕ=0.35; [TbIIIL2]+, H2O, 298 K, τ=1.95 ms, ϕ=0.68). Together with the very high kinetic and thermodynamic stabilities, these complexes are a possible basis for interesting biological probes.

Regulating the distortion degree of the square antiprism coordination geometry in Dy–Na single ion magnets

A DyNa complex (1) and a DyNa2 1D chain (2) have been obtained; their square antiprism coordination geometries were changed from the bicapped triangular prism of the reported DyNa2 complex. Compounds 1 and 2 exhibit single ion magnet behavior.

A Molecular Crystal Shows Multiple Correlated Magnetic and Ferroelectric Switchings

Simultaneous control of the magnetic and electric properties of materials is crucial for their application in next-generation memory and sensor devices. Herein, we report a single-crystal Co(II) co...

Supramolecular structures, thermal decomposition mechanism and heat capacity of the novel binuclear Tb(III) and Dy(III) complexes with 2,3-dimethoxybenzoic acid and 5,5′-dimety-2,2′-bipyridine

Two novel binuclear lanthanide complexes [Tb(2,3-DMOBA)3(5,5′-DM-2,2′-bipy)]2·C2H5OH (1) and [Dy(2,3-DMOBA)3(5,5′-DM-2,2′-bipy)]2·C2H5OH (2) (2,3-DMOBA = 2,3-dimethoxybenzoate, 5,5′-DM-2,2′-bipy = 5,5′-dimety-2,2′-bipyridine) have been successfully synthesized and structurally validated by single-crystal diffraction. The results of single-crystal analyses indicate the complexes contains one free ethanol molecule, and each center Ln(III) is nine-coordinated, exhibiting a distorted monocapped square anti-prismatic coordination geometry. The two center Ln(III) are bound by four 2,3-DMOBA ligands, two of which are bridging bidentate and the other two are bridging–chelating. The adjacent binuclear complexes can form 1D supramolecular structure by a pair of alternating identical C–H···O hydrogen bonding interactions, which further form 2D sheet structures. The thermal behavior of these complexes is investigated by TG-DSC/FTIR. What is more, the heat capacities of the complexes 1–2 are measured by DSC at 259.15–346.15 K, and the result indicates that the heat capacity values of the complexes gradually increased with the increase in temperature. In addition, the thermodynamic functions values (HT − H298.15K) and (ST − S298.15K) of the complexes 1–2 are calculated according to the fitted polynomial equations and the thermodynamic equation. The luminescence property of complex 1 is studied.

Differences in the Relaxometric Properties of Regioisomeric Benzyl-DOTA Bifunctional Chelators: Implications for Molecular Imaging.

The bifunctional chelator S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane- N, N', N″, N‴-1,4,7,10-tetraacetate (IB-DOTA) is on paper the most attractive of the commercially available bifunctional chelators for magnetic resonance imaging (MRI) applications. The preserved DOTA scaffold is known to produce extremely kinetically and thermodynamically robust chelates with the Gd3+ ion. Also, ligation through four acetate pendant arms should ensure that the rapid water exchange kinetics so, crucial to the function of an MRI contrast agent are retained. However, upon ligation of the Gd3+ ion, IB-DOTA differentiates into two distinct isomers defined by the positions of the benzylic substituent (corner or side). A relaxometric analysis of these two isomers revealed marked differences in the property and behavior of the two chelates. Most notably the side isomer is found to be substantially more likely to aggregate in aqueous solution than its corner counterpart. This aggregation results in higher relaxivity for the side isomer versus the corner isomer, an observation that potentially obscures the impact of differences in water exchange kinetics between the two isomers. The side isomer is composed of a significant fraction of a twisted square antiprismatic coordination geometry that exchanges water more rapidly than optimal (τM = 7 ns) for maximizing relaxivity. The impact of this excessively fast exchange is not observed in the relaxivity of the side isomer only because in isolation this chelate tumbles much more slowly than the corner isomer. However, this situation is not expected to persist when the chelate is employed in a typical bioconjugate. These results imply that the corner isomer of IB-DOTA may represent a better choice of bifunctional chelator for bioconjugation applications in which a large macromolecule is to be tagged for MRI applications.

Lanthanide complexes with 3-methoxybenzoic acid and 5,5′-dimethyl-2,2′-bipyridine: Crystal structures, luminescence and magnetic property

Five dinuclear trivalent lanthanide complexes, [Ln(3-MOBA)3(5,5′-DM-2,2′-bipy)]2 (Ln = Er(1), Ho(2), Eu(3), Pr(4), Nd(5); 3-MOBA = 3-methoxybenzoate; 5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine) have been successfully synthesized via conventional solution method at room temperature and structurally characterized by single crystal and powder X-ray diffraction. The molecular structures of complexes 1–5 are very novel-innovative. Complexes 1 and 2 were isomorphic, and the complex 1 was obtained with the coordination number of eight to form a distorted square-antiprism coordination geometry, while complexes 3–5 were nine-coordinated with a distorted monocapped square antiprismatic coordination geometry, but they can be all assembled into the same 1D, 2D supramolecular structure, which has rarely been reported previously. Over the temperature range of 300–1200 K, the thermal decomposition mechanism of complexes 1–5 were discussed by the technology of TG/DSC-FTIR. The luminescence spectra of complex 3 displayed the characteristic emission of Eu3+ ion (5D0 → 7F0-4), and it’s CIE coordinate was also calculated as (0.647, 0.341). In addition, the luminescence lifetime and intrinsic luminescence quantum yield were also investigated. Beyond that, the magnetic properties of complexes 1–2 were studied in detail.

On the consequences of the stereochemical activity of the Bi(iii) 6s2 lone pair in cyclen-based complexes. The [Bi(DO3A)] case.

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(iii) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(iii) ions thanks to μ2-η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(iii) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(iii) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(iii) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (ε = 8770 M-1 cm-1) that was attributed to the Bi(iii)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl-, Br-, I- and N3-, respectively.

Structural Variability of 4f and 5f Thiocyanate Complexes and Dissociation of Uranium(III)-Thiocyanate Bonds with Increased Ionicity.

A series of complexes [Et4N][Ln(NCS)4(H2O)4] (Ln = Pr, Tb, Dy, Ho, Yb) have been structurally characterized, all showing the same structure, namely a distorted square antiprismatic coordination geometry, and the Ln-O and Ln-N bond lengths following the expected lanthanide contraction. When the counterion is Cs+, a different structural motif is observed and the eight-coordinate complex Cs5[Nd(NCS)8] isolated. The thorium compounds [Me4N]4[Th(NCS)7(NO3)] and [Me4N]4[Th(NCS)6(NO3)2] have been characterized, and high coordination numbers are also observed. Finally, attempts to synthesize a U(III) thiocyanate compound has been unsuccessful; from the reaction mixture, a heterocycle formed by condensation of five MeCN solvent molecules, possibly promoted by U(III), was isolated and structurally characterized. To rationalize the inability to isolate U(III) thiocyanate compounds, thin-layer cyclic voltammetry and IR spectroelectrochemistry have been utilized to explore the cathodic behavior of [Et4N]4[U(NCS)8] and [Et4N][U(NCS)5(bipy)2] along with a related uranyl compound [Et4N]3[UO2(NCS)5]. In all examples, the reduction triggers a rapid dissociation of [NCS]- ions and decomposition. Interestingly, the oxidation chemistry of [Et4N]3[UO2(NCS)5] in the presence of bipy gives the U(IV) compound [Et4N]4[U(NCS)8], an unusual example of a ligand-based oxidation triggering a metal-based reduction. The experimental results have been augmented by a computational investigation, concluding that the U(III)-NCS bond is more ionic than the U(IV)-NCS bond.

Metallacrowns as Templates for Diabolo-like {LnCu8 } Complexes with Nearly Perfect Square Antiprismatic Geometry.

A series of diabolo-like nonanuclear {LnIII CuII8 } (Ln=Tb, Dy, Ho, Er, Tm, Yb, and Y) clusters were prepared in which the LnIII ion is capped by two 8-MC-4 metallacrown ligands to form a nearly ideal square antiprismatic (SAP) coordination geometry with D4d symmetry. Despite the lack of crystallographic symmetry, these molecules engender the lanthanide ions with highly axial mJ states. The axial/equatorial nature of the crystal field in environments close to ideal SAP geometry is very subtle and influenced by the nature of the ligand lone pairs. Slow magnetic relaxation behaviour was observed for the DyIII , ErIII , TmIII , and YbIII analogues, and the obtained effective energy barriers are not consistent with excitations on the LnIII ion, suggesting a more nuanced situation.

Synthesis, crystal structures, luminescence and thermal properties of lanthanide complexes containing 2,5-dichlorobenzoic acid and 2,2:6′,2″-terpyridine

Three novel ternary lanthanide complexes [Ln(2,5-DClBA)3(terpy)(H2O)] (Ln = Eu (1), Tb (2), Ho (3), 2,5-DClBA = 2,5-dichlorobenzoate, terpy = 2,2:6′,2″-terpyridine) have been successfully synthesized and characterized by single-crystal and powder X-ray diffraction. Complexes 1–3 are isostructural, and each metal center is nine-coordinated with distorted monocapped square antiprismatic coordination geometry. The mononuclear units are assembled into 1D, 2D, 3D supramolecular structures by the π–π stacking and halogen–halogen interactions. Thermal decomposition mechanisms of the title complexes were investigated by thermogravimetric analysis and further authenticated by TG/DSC-FTIR techniques. The solid-state fluorescent properties of complexes 1–2 were studied at room temperature, and characteristic emission was observed for all complexes. Complex 1 exhibits the strong red emission, while the complex 2 is green under UV light. Moreover, the antibacterial activities of the complexes against Candida albicans, Escherichia coli and Staphylococcus aureus were also evaluated.

Construction of two novel lanthanide complexes supported by 2-bromine-5-methoxybenzoate and 2,2′-bipyridine: Syntheses, crystal structures and thermodynamic properties

Two novel lanthanide complexes with the general formula [Ln(2-Br-5-MOBA)3(2,2′-DIPY)]2 (Ln=Pr(1), Dy(2); 2-Br-5-MOBA=2-bromine-5-methoxybenzoate; 2,2′-DIPY=2,2′-bipyridine) have been successfully synthesized and characterized. The complexes 1 and 2 are isostructural and nine-coordinated with distorted monocapped square antiprismatic coordination geometry by the single-crystal X-ray diffraction analyses. Two complexes are all assembled into the 1D, 2D, 3D supramolecular structures by CH⋯O hydrogen bonding and π–π stacking interactions. The thermal decomposition mechanism for title complexes were obtained by TG/DSC-FTIR technology. The molar heat capacities of the complexes 1 and 2 are measured by a DSC instrument over the temperature range from 263.15K to 365.15K. On the basis of the fitted polynomial and thermodynamic equations, the smoothed values of heat capacities and thermodynamic functions (HT-H298.15K), and (ST-S298.15K) of the two complexes are calculated. In addition, the fluorescence spectra indicate that the complex 2 exhibits the characteristic emission of Dy(III) ion (4F9/2→6H13/2–15/2).

Structures and optical spectroscopy of lanthanide trifluoroacetates obtained from hexafluoroacetylacetone

Several lanthanide trifluoroacetate complexes with 2,2′-bipyridine (Bpy) and 1,10-phenanthroline (Phen) prepared in an unusual method from hexafluoroacetylacetone (H-hfa) have been investigated using single crystal X-ray analysis, photoluminescence and IR spectroscopy. The triclinic crystal structures of [Ln(CF3CO2)3·Bpy·(H2O)3]·Bpy (Ln=Eu (1), Tb (2)) contain outersphere Bpy molecules. The structure of the compound [Eu(CF3CO2)3·Phen·(H2O)3]·Phen (3) is identical to 1 and 2 ones. A distorted square antiprismatic coordination geometry of the Ln3+ luminescence center, lifetimes of the 5D0 (Eu3+) and 5D4 (Tb3+) emitting states, luminescence efficiencies and energy transfer processes are discussed. Analysis of the relative energies of the lowest excited singlet and triplet states of the ligands and the electronic states of the Ln3+ ions showed that the most efficient luminescence excitation in the trifluoroacetates is realized through the auxiliary ligand. The results obtained were compared with available data for lanthanide acetates and β-diketonates. This study can be useful in the identification of lanthanide products synthesized from H-hfa, when the formation of mixtures of hexafluoroacetylacetonate and trifluoroacetate or the complete “replacement” of the final compound is a real problem.

Dinuclear complexes of europium(III) and gadolinium(III) ions with a julolidine–quinoline-based tridentate ligand

The reaction of europium(III) or gadolinium(III) acetates with a Schiff base ligand {HL (C22H21N3O) = ((E)-9-((quinolin-8-ylimino)methyl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-8-ol)} in methanol affords two dinuclear complexes which have been characterized by powder X-ray diffraction, Raman spectroscopy, scanning electron microscope–electron dispersive spectroscopy, absorption and emission spectroscopies as well as single-crystal X-ray diffraction. [Eu2L2(CH3COO)4(CH3OH)2] (1) and [Gd2L2(CH3COO)4(CH3OH)2] (2) are iso-structures, each consisting of two M : L : CH3COO : CH3OH (1 : 1 : 1 : 1) units bridged by two acetate anions with the metal center in a distorted capped square antiprismatic coordination geometry. Their vibration modes, electronic structures, and photoluminescent properties are reported.