EuIII Ions Research Articles

Hydroxyquinoline–Calix[4]arene Conjugates as Ligands for Polynuclear Lanthanide Complexes: Preparation, Characterization, and Properties of a Dinuclear EuIII Complex

The synthesis of calixarene‐based N4O4‐donor ligand H6L, in which two 8‐hydroxyquinoline‐2‐carbaldehyde units are appended via hydrazone‐carbonylmethoxy linkages in a 1,3 arrangement to the lower rim of tert‐butylcalix[4]arene, and its coordination properties towards EuIII are described. The reaction of H6L with Eu(NO3)3·6H2O produced dinuclear complex [Eu2(H3L)2(MeCN)2] (4). The EuIII ions in 4 are well separated from each other (d > 8 Å) and each is coordinated by two tetradentate hydroxyquinoline‐2‐carbaldehyde hydrazone substituents from two triply deprotonated (H3L)3– ligands in a dodecahedral geometry. As a consequence there are no exchange interactions between the EuIII ions, and the magnetic properties are solely associated with thermal population of excited (7F1–7F6) terms. The spin–orbit coupling constant λ is 325.2(4) cm–1. Moreover, H6L was found to extract EuIII and TbIII from aqueous solution at pH 7–8, as established by radiotracing with 160Tb and 152Eu.

A green-emitting iridium complex used for sensitizing europium ion with high quantum yield

A green-emitting iridium(III) complex Ir(dfppy)2(cbphen) (dfppy=2-(4′,6′-difluoro-phenyl)pyridine, cbphen=4-carboxylate-phenanthroline) was synthesized and fully characterized. The single crystal data confirm its Ir(C^N)2(N^N) structure with the carboxylate group on phenanthroline stretching freely which could be able to combine with europium(III) ion. The complex was reacted with EuCl3·6H2O and Eu(TTA)3·2H2O to provide bimetallic complexes. Through photophysical studies, characteristic emission from EuIII ion was obtained, and meanwhile the green emission from iridium(III) center was almost quenched completely, suggesting this iridium(III) complex is a good sensitizer for EuIII ions. It is well worth noticing that by introducing the iridium(III) complex as a chromophore, the excitation wavelength of EuIII ion has been extended to the visible range (470nm). Besides, due to the efficient energy transfer, the quantum yield of Ir3-Eu was nearly equal to that of Eu(TTA)3·2H2O.

Selective Extraction of Americium(III) over Europium(III) Ions with Pyridylpyrazole Ligands: Structure–Property Relationships

To clarify the structure–property relationships of pyridylpyrazole ligands and provide guidance for the design of new and more efficient ligands for the selective extraction of actinides over lanthanides, a series of alkyl‐substituted pyridylpyrazole ligands with different branched chains at different positions of the pyrazole ring were synthesized. Extraction experiments showed that the pyridylpyrazole ligands exhibited good selective extraction abilities for AmIII ions, and the steric effects of the branched chain had a significant impact on the distribution ratios of AmIII and EuIII ions as well as the separation factor. Moreover, both slope analyses and UV/Vis spectrometry titrations indicated the formation of a 1:1 complex of 2‐(1‐octyl‐1H‐pyrazol‐3‐yl)pyridine (C8‐PypzH) with EuIII ions. The stability constant (log K) for this complex obtained from the UV/Vis titration was 4.45 ± 0.04. Single crystals of the complexes of 3‐(2‐pyridyl)pyrazole (PypzH) with Eu(NO3)3 and Sm(NO3)3 were obtained; PypzH acts as a bidentate ligand in the crystal structures, and the N atom with a bound H atom did not participate in the coordination. In general, this study revealed some interesting findings on the effects of the alkyl‐chain structure and the special complexation between pyridylpyrazole ligands and LnIII ions.

Series d-f Heteronuclear Metal-Organic Frameworks: Color Tunability and Luminescent Probe with Switchable Properties.

A series of five unique d-f heteronuclear luminescent metal-organic frameworks (MOFs) in an entangled polyrotaxane array and the light-harvesting block homonuclear zinc compound have been isolated successfully and characterized. The series of isostructural polymers feature 3,4-connected (4.82)(4.83.92)(6.8.9)2(6.92)(83) topology and high stability, exhibiting diverse void spaces. By taking advantage of the isostructural MOFs 2 and 3, the intensities of red and green emissions can be modulated by adjusting the ratios of EuIII and TbIII ions correspondingly, and white-light emission can be generated by a combination of different doped TbIII and EuIII concentrations. The Tb-Zn-based framework {[Tb3Zn6(bipy2)2(Hmimda)7 (H2O)3]·5H2O}n (3; H3mimda = 2-methyl-1-H-imidazole-4,5-dicarboxylic acid and bipy = 4,4'-bipyridine) can detect trace MgII ion with relatively high sensitivity and selectivity. Dehydrated MOF 3a shows a remarkable emission quenching effect through the introduction of I2 solids. Further investigation indicates that it exhibits turn on/off switchable properties for small solvent molecules or heavy-metal ions. Steady/transient-state near-IR luminescence properties for MOFs 1, 4, and 5 were investigated under visible-light excitation.

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.

Time-Gated Detection of Cystathionine γ-Lyase Activity and Inhibition with a Selective, Luminogenic Hydrogen Sulfide Sensor.

Herein, we report the design, synthesis, and characterization of a lanthanideIII complex-based probe for the time-gated luminescence detection of hydrogen sulfide (H2 S) in aqueous media. The probe's unique sensing mechanism relies on the selective reduction of azide to amine by sulfide, followed by intramolecular cyclization to form a quinolinone. The quinolinone is a sensitizer that absorbs near-UV light and transfers excitation energy to coordinated TbIII or EuIII ions to trigger a strong "turn-on" luminescence response with ms-scale lifetimes characteristic of lanthanide complexes. Using this probe, we developed a robust, high throughput screening (HTS) assay for detecting H2 S generated by cystathionine γ-lyase (CSE), one of the main producers of H2 S in mammalian cells. In a 240-compound screen to identify potential CSE inhibitors, the EuIII analogue of the sensor showed a low false-positive rate and high Z'-factor (>0.7).

Luminescent Europium(III) Coordination Zippers Linked with Thiophene‐Based Bridges

AbstractNovel EuIII coordination polymers [Eu(hfa)3(dpt)]n (dpt: 2,5‐bis(diphenylphosphoryl)thiophene) and [Eu(hfa)3(dpedot)]n (dpedot: 2,5‐bis(diphenylphosphoryl)ethylenedioxythiophene) with hydrogen‐bonded zipper structures are reported. The coordination polymers are composed of EuIII ions, hexafluoroacetylacetonato ligands, and thiophene‐based phosphine oxide bridges. The zig‐zag orientation of single polymer chains induced the formation of densely packed coordination structures with multiple intermolecular interactions, resulting in thermal stability above 300 °C. They exhibit a high intrinsic emission quantum yield (ca. 80 %) due to their asymmetrical and low‐vibrational coordination structures around EuIII ions. Furthermore, the characteristic alternative orientation of substituents also contributes to the dramatically high ligand‐to‐metal energy transfer efficiencies of up to 80 % in the solid state.

Exploring the Nature of the Nanocavity and Channels in Apoferritin and Apoferritin–Sodium Dodecyl Sulfate Complex Using an Enhanced Antenna Effect through the Encapsulation of EuIII–Tetracycline

The drug tetracycline hydrochloride (TC), which has cytotoxic and cytostatic effects on tumor cells, has been encapsulated within the nanocavity of apoferritin in the form of its EuIII complex (Eu3TC). The Eu3TC complex was encapsulated within apoferritin through disassembly followed by reassembly of the protein and exhibited significantly enhanced EuIII emission in comparison with that of free Eu3TC in aqueous buffer at pH 8. The steady‐state and transient measurement of the emission of each species in the ternary system suggest that the effective sensitization of EuIII emission may be ascribed to a comparatively rigid environment for the bound TC after encapsulation that promotes efficient energy transfer to the EuIII ions. Emission studies in D2O revealed that the microenvironment of the EuIII ion is shielded from O–H oscillators in the ternary system, and the extent of shielding is greater after the encapsulation of the complex within the apoferritin cavity. The rotational correlation time (θc) of bound TC and docking studies also support the contention that the TC is in a more buried environment after encapsulation within the apoferritin cavity. A competition study with sodium dodecyl sulfate (SDS) revealed that SDS does not interfere with the binding of TC to apoferritin. The biocompatible system consisting of Eu3TC encapsulated within the cavity of apoferritin may be used as an efficient targeted drug transporter, and the sensitization of the EuIII emission may also enable its use as a biosensor.

Intra‐ and inter‐supramolecular complexation of poly(butyl methacrylate)‐co‐2‐(1,2,3‐triazol‐4‐yl)pyridine copolymers induced by CoII, FeII, and EuIII ions monitored by molecular hydrodynamics methods

ABSTRACTPoly(butyl methacrylate) copolymers embedding bidentate 2‐(1,2,3‐triazol‐4‐yl)pyridine (trzpy) chelating units as comonomer in the side chains were synthesized by controlled radical addition‐fragmentation transfer (RAFT) polymerization. Intracomplexation and intercomplexation of the macromolecules of the poly(butyl methacrylate) copolymers containing 20 % mol of trzpy units induced by CoII, FeII, and EuIII ions were studied in the solutions by macromolecular hydrodynamics methods. The sedimentation velocity of extremely diluted copolymer solutions and the dynamic viscosity of moderately diluted solutions were studied in a wide range of the salts concentrations. Differences were observed with respect to the copolymer behavior in the presence of the Co2+, Fe2+, Eu3+ ions. These differences are namely due to the differences in the number of coordination bonds required for complex formation and not explicitly to the nature of the corresponding anions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2632–2639

Hyper-stable organo-Eu(III) luminophore under high temperature for photo-industrial application.

Novel organo-EuIII luminophores, Eu(hfa)x(CPO)y and Eu(hfa)x(TCPO)y (hfa: hexafluoroacetylacetonate, CPO: 4-carboxyphenyl diphenyl phosphine oxide, TCPO: 4,4′,4″-tricarboxyphenyl phosphine oxide), were synthesized by the complexation of EuIII ions with hfa moieties and CPO or TCPO ligands. The thermal and luminescent stabilities of the luminophores are extremely high. The decomposition temperature of Eu(hfa)x(CPO)y and Eu(hfa)x(TCPO)y were determined as 200 and 450 °C, respectively. The luminescence of Eu(hfa)x(TCPO)y under UV light irradiation was observed even at a high temperature, 400 °C. The luminescent properties of Eu(hfa)x(CPO)y and Eu(hfa)x(TCPO)y were estimated from emission spectra, quantum yields and lifetime measurements. The energy transfer efficiency from hfa moieties to EuIII ions in Eu(hfa)x(TCPO)y was 59%. The photosensitized luminescence of hyper-stable Eu(hfa)x(TCPO)y at 400 °C is demonstrated for future photonic applications.

Theoretical Modeling of the Magnetic Behavior of Thiacalix[4]arene Tetranuclear Mn(II)2Gd(III)2 and Co(II)2Eu(III)2 Complexes.

In view of a wide perspective of 3d-4f complexes in single-molecule magnetism, here we propose an explanation of the magnetic behavior of the two thiacalix[4]arene tetranuclear heterometallic complexes Mn(II)2Gd(III)2 and Co(II)2Eu(III)2. The energy pattern of the Mn(II)2Gd(III)2 complex evaluated in the framework of the isotropic exchange model exhibits a rotational band of the low-lying spin excitations within which the Landé intervals are affected by the biquadratic spin-spin interactions. The nonmonotonic temperature dependence of the χT product observed for the Mn(II)2Gd(III)2 complex is attributed to the competitive influence of the ferromagnetic Mn-Gd and antiferromagnetic Mn-Mn exchange interactions, the latter being stronger (J(Mn, Mn) = -1.6 cm(-1), Js(Mn, Gd) = 0.8 cm(-1), g = 1.97). The model for the Co(II)2Eu(III)2 complex includes uniaxial anisotropy of the seven-coordinate Co(II) ions and an isotropic exchange interaction in the Co(II)2 pair, while the Eu(III) ions are diamagnetic in their ground states. Best-fit analysis of χT versus T showed that the anisotropic contribution (arising from a large zero-field splitting in Co(II) ions) dominates (weak-exchange limit) in the Co(II)2Eu(III)2 complex (D = 20.5 cm(-1), J = -0.4 cm(-1), gCo = 2.22). This complex is concluded to exhibit an easy plane of magnetization (arising from the Co(II) pair). It is shown that the low-lying part of the spectrum can be described by a highly anisotropic effective spin-(1)/2 Hamiltonian that is deduced for the Co(II)2 pair in the weak-exchange limit.

Synthesis, Structure, and Fluorescent Properties of Lanthanide Complexes Based on 8‐Hydroxyquinoline‐7‐carboxylic Acid

AbstractThe lanthanide complex [Eu3(8‐HQCA)3(COOH)(OH)2(H2O)3]n·nH2O (8‐HQCA = 8‐hydroxyquinoline‐7‐carboxylic acid) was synthesized and characterized. Single‐crystal X‐ray diffraction shows that the trinuclear structures are linked by ligands to form 2D layers. The results of DFT calculation shows that energy can be transferred effectively from the ligand to EuIII ions. A series of heteronuclear complexes {[(Eu1–xYx)3(8‐HQCA)3(COOH) (OH)2(H2O)3]n·nH2O (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8)} were synthesized and their luminescent properties were studied. The results showed that the doping of YIII ions could change the fluorescent intensity of the EuIII complex, but could not change their positions.

First examples of carbacylamidophosphate pentanuclear hydroxo-complexes: Synthesis, structure, luminescence and magnetic properties

The first representatives of pentanuclear carbacylamidophosphate complexes of composition Ln5L6(μ-L)4(μ3-OH)4(μ4-OH) (LnIII=Eu (1), Gd (2), Tb (3), L−=dimethylbenzoylamidophosphate ion [C6H5C(O)–N–P(O)(OCH3)2]−) were obtained. The single crystal X-ray analysis revealed that polynuclear core of 1 contains five europium ions, connected by the μ3- and μ4-hydroxo groups and carbacylamidophosphate ligands. Compounds 1–3 were found to be isostructural. Temperature dependencies of magnetic susceptibility (χM) of the compounds 1 and 2 could be explained by spin-orbit coupling of EuIII ions or antiferromagnetic exchange interactions of four GdIII ions located in the base of Gd5 pyramid, respectively. In the case of 3, the value of χM increases with temperature decreasing from 300K to 50K, and then falls down during temperature decrease till 2K. Such behavior can be explained by comparable contribution of spin-orbit coupling and exchange interactions. No signs of single-molecule magnet behavior for 3 were found at 2K. Phosphorescence, emission and excitation spectra at 298K and 77K for the complexes were measured, as well as luminescence decay times were determined. The compounds 1 and 3 showed intense luminescence with decay time at 298K equal to 0.66 and 1.44ms respectively. Intrinsic quantum yield for 1 determined from its emission spectrum was found to be 25%.

Structure and luminescent properties of 2D Salen-type lanthanide coordination polymers from the flexible N,N′-bis(salicylidene)-1,4-butanediamine ligand

Three new Salen-type lanthanide coordination polymers, [Ln2(H2L)2(NO3)4(CH3O)2]n (Ln=Sm (1), Eu (2) and Lu (3); H2L=N,N′-bis(salicylidene)-1,4-butanediamine), have been synthesized by a solvothermal method and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra and thermogravimetric analysis. Single-crystal X-ray diffraction studies reveal that complexes 1–3 are isostructural 2D coordination polymers based on dinuclear units, where the μ2-(methoxy-O)2-bridged Ln2O2 cores are linked by four Salen-type ligands in a bidentate mode. Each lanthanide ion is eight-coordinated by eight oxygen atoms, forming a distorted dodecahedral geometry. Luminescence analysis in the solid state at room temperature indicates that complex 1 exhibits the co-luminescence of the ligand and SmIII ions and complex 2 shows the characteristic red luminescence of EuIII ions. Furthermore, the energy transfer mechanisms are described and discussed.

Influence of Metal Cations and Coordination Modes on Luminescent Group 1 and 2 Metal Sulfonate Complexes Constructed from 4,4′‐Dihydroxybiphenyl‐3,3′‐disulfonic Acid

The reactions of 4,4′-dihydroxybiphenyl-3,3′-disulfonic acid (H4L) with group 1 and 2 metal salts in aqueous solution lead to six metal sulfonate complexes, [K2(H2L)]n (1), {[Cs2(H2L)(H2O)]n·nH2O} (2), 2[Mg(H2O)6]2+·2(H2L)2–·2H2O (3), {[Ca(H2L)(H2O)2]n·4nH2O} (4), {[Sr(H2L)(H2O)4]n·3nH2O} (5), and {[Ba(H2L)(H2O)]n·nH2O} (6), which have been characterized by elemental analysis, IR spectroscopy, thermogravimetry (TG), photoluminescence (PL) spectroscopy, powder XRD, and single-crystal XRD. Complexes 1, 2, and 6 exhibit 3D pillared-layered networks formed by M–O–S layers bridged by the biphenyl rings of H2L2– dianions. The [Mg(H2O)6]2+ cations and sulfonate groups in 3 are held together by second-sphere interactions to generate layer motifs. Complex 4 presents a layer structure formed by Ca–O chains bridged by the biphenyl rings of H2L2– dianions. Complex 5 has a 3D interdigitating architecture (2D + 2D 3D), in which the 44 hydrogen-bonding layer is constructed from linear chains. Meanwhile, the recrystallization of H4L from aqueous solution affords the supramolecular complex 2(H3O+)·(H2L)2–·3H2O (S1), which exhibits a 3D pillared-layered network. The solid-state luminescence properties demonstrate that 1–6 exhibit violet emission at room temperature and can sensitize EuIII and TbIII ions to exhibit their characteristic emissions.

Aqueous Complexation of YIII, LaIII, NdIII, SmIII, EuIII, and YbIII with Some Heterocyclic Substituted β‐Diketones

AbstractThis paper deals with spectrophotometric investigation on complexation of YIII, LaIII, NdIII, SmIII, EuIII, and YbIII metal ions with six heterocyclic substituted β‐diketones. The stability constants of 36 monocomplex species was determined in aqueous solutions at 298 K and I = 0.25; it lay in the range from 5.14 to 9.76 logarithmic units. The influence of the natures of the metal and ligand on the stability constant along with the dependence of the stability constant on an ionic potential (z/r) was studied and is discussed. The acid–base, tautomeric, and dimeric equilibriums of the studied substituted β‐diketones have been investigated using UV/Vis and 1H NMR spectroscopy. Also, ab initio calculations of electronic structures of metal aquacomplex species, anions of β‐diketones, and their complex species have been carried out.

Four two-dimensional lanthanide(III)-4,4-biphenyldicarboxylate complexes: Syntheses, structures, magnetic and luminescent properties

Four novel Ln-bpdc coordination polymers [Ln(bpdc)(NO3)(DMA)2] [Ln=La(1), Pr(2), Sm(3), Eu(4)] [Ln=lanthanide, H2bpdc=4,4-biphenyldicarboxylate acid and DMA=dimethylacetamide] have been solvothermally synthesized and structurally characterized by elemental analyses, IR spectra and single-crystal X-ray diffraction. 1–4 crystallize in the monoclinic space group P21/c and show a 2-D layer constructed from 1-D Ln–organic chain and tetradentate bpdc2− ligand. The magnetic behavior of 2–4 has been investigated. The solid-state photoluminescent measurement illustrates that Eu(4) displays the strong fluorescent emissions, which demonstrate that π-rich aromatic organic bpdc2− ligands can efficiently transfer energy to the EuIII ions. In addition, thermogravimetric analysis of Pr(2) is also described.

Syntheses, Structures, and Fluorescent Properties of ­Lanthanide Complexes Based on the Ligand Benzotriazole‐5‐carboxylic Acid

AbstractThree lanthanide complexes with the formula [Ln(Hbtca)3(4,4′‐bpy)(H2O)2]n·nH2O [Ln = Eu (1), Gd (2), Tb (3)] (4,4′‐bpy = 4,4′‐bipyridine; H2btca = benzotriazole‐5‐carboxylic acid) were synthesized and characterized. Single‐crystal X‐ray diffraction analysis shows that complexes 1–3 possess 1D chain structures. There are O–H···N, O–H···O, and N–H···N hydrogen bonds, which result in the formation of 3D supramolecular networks. When excited at 360 nm, complexes 1 and 3 give characteristic emissions of EuIII and TbIII ions, respectively, whereas in the mixed Eu/Tb complex, EuIII emissions are strengthened and TbIII emissions are quenched, which indicates that energy may be transferred from TbIII to EuIII ions.

A Series of Exceptionally Robust Luminescent Coordination Polymers Based on a Bipyridyldicarboxylate Ligand and Rare‐Earth‐Metal Ions

AbstractA series of three‐dimensional rare‐earth coordination polymers, [M2(bpdc)3(H2O)4] (M = Y [1], Sm [2], Eu [3], Gd [4], Tb [5], Dy [6], Er [7], and Yb [8]) were synthesized by solvothermal reactions of 2,2′‐bipyridine‐5,5′‐dicarboxylate (bpdc) with corresponding metal salts. Single‐crystal and powder X‐ray diffraction analyses demonstrated that these coordination polymers are isostructural. The carboxyl groups of the bpdc ligand are coordinated to metal ions and the 2,2′‐bipyridine moieties are left free due to the preferable affinity of rare‐earth metals for oxygen‐donor atoms. The adjacent eight‐coordinate MO8 cores show dicapped trigonal prismatic environments; they are interconnected by carboxyl groups and are further bridged through the bipyridyl linkers to give quite dense three‐dimensional networks. Photoluminescent studies at room temperature reveal intense red and green luminescent emissions for EuIII and TbIII analogues, respectively. Furthermore, it is noteworthy that bpdc shows an effective antenna effect in sensitizing emissions from EuIII and TbIII ions. Thermogravimetric analyses demonstrate that these coordination polymers exhibit exceptional thermal stability (decomposing at T > 580 °C under N2 for compound 1). Water‐resistance measurements of these coordination polymers show excellent hydrothermal stability.

Effect of Ligand Polarization on Asymmetric Structural Formation for Strongly Luminescent Lanthanide Complexes

AbstractThe effect of ligand polarization on the formation of strongly luminescent lanthanide complexes with asymmetric structures is described for the first time. The lanthanide complexes are composed of EuIII ions, three hexafluoroacetylacetonate (hfa) ligands, and two monodentate phosphine oxide ligands, namely, triphenylphosphine oxide (TPPO), p‐tolyldiphenylphosphine oxide (TPPO‐Me), tri‐p‐tolylphosphine oxide (TPPO‐3Me) or o‐phenoxyphenyldiphenylphosphine oxide (TPPO‐OPh). The luminescence properties of the EuIII complexes are characterized by their emission quantum yields, emission lifetimes, and their radiative (kr) and nonradiative (knr) rate constants. The EuIII complex with TPPO‐OPh ligands offers a markedly high emission quantum yield (72 % in [D6]acetone, 85 % in the solid state) owing to enhancement of the electric dipole transition and suppression of vibrational relaxation, which are directly related to kr and knr. The coordination geometries of the EuIII complexes are categorized by shape‐measure calculations. The EuIII complexes exhibit characteristic square‐antiprismatic or trigonal‐dodecahedral structures, depending on the ligand polarization. Strongly luminescent Eu(hfa)3(TPPO‐OPh)2 has an asymmetric dodecahedron structure. The formation of distorted dodecahedral structures with low vibrational frequencies for the enhancement of luminescence is elucidated in terms of the ligand polarization of the monodentate phosphine oxide ligands in the EuIII complexes.