Metal‐Ion Sensing Europium(III) Complexes with Bidentate Phosphine Oxide Ligands Containing a 2,2′‐Bipyridine Framework

Novel Eu^III complexes with bidentate phosphine oxide ligands containing a bipyridine framework, i.e., [3,3′‐bis(diphenylphosphoryl)‐2,2′‐bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(BIPYPO)]) and [3,3′‐bis(diphenylphosphoryl)‐6,6′‐dimethyl‐2,2′‐bipyridine]tris(hexafluoroacetylacetonato)europium(III) ([Eu(hfa)₃(Me‐BIPYPO)]), were synthesized for lanthanide‐based sensor materials having high emission quantum yields and effective chemosensing properties. The emission quantum yields of [Eu(hfa)₃(BIPYPO)] and [Eu(hfa)₃(Me‐BIPYPO)] were 71 and 73%, respectively. Metal‐ion sensing properties of the Eu^III complexes were also studied by measuring the emission spectra of Eu^III complexes in the presence of Zn^II or Cu^II ions. The metal‐ion sensing and the photophysical properties of luminescent Eu^III complexes with a bidentate phosphine oxide containing 2,2′‐bipyridine framework are demonstrated for the first time.     

Synthesis,Crystal Structure,Fluorescent and Antioxidation Properties of Cerium(III) and Europium(III) Complexes with Bis(3‐methoxysalicylidene)‐3‐oxapentane‐1,5‐diamine

Two aliphatic ether Schiff base lanthanide complexes (Ln = Eu, Ce) with bis(3‐methoxysalicylidene)‐3‐oxapentane‐1,5‐diamine (Bod), were synthesized and characterized by physicochemical and spectroscopic methods. [Eu(Bod)(NO₃)₃] ( 1 ) is a discrete mononuclear species and [Ce(Bod)(NO₃)₃DMF]_∞ ( 2 ) exhibits an inorganic coordination polymer. In the two complexes, the metal ions both are ten‐coordinated and the geometric structure around the Ln^III atom can be described as distorted hexadecahedron. Under excitation at room temperature, the red shift in the fluorescence band of the ligand in the complexes compared with that of the free ligand can be attributed to coordination of the rare earth ions to the ligand. Moreover, the antioxidant activities of the two complexes were investigated. The results demonstrated that the complexes have better scavenging activity than both the ligand and the usual antioxidants on the hydroxyl and superoxide radicals.     

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p, H₆ L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H₄dota and H₈dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several Ln^III–H₆ L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H₂O)]^3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the ¹H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H₂O)]^2? and [Yb(H L )]^2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between ³¹P/¹H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N₄ and O₄ planes.     

Remarkable Tuning of the Coordination and Photophysical Properties of Lanthanide Ions in a Series of Tetrazole‐Based Complexes

A series of seven new tetrazole‐based ligands (L1, L3–L8) containing terpyridine or bipyridine chromophores suited to the formation of luminescent complexes of lanthanides have been synthesized. All ligands were prepared from the respective carbonitriles by thermal cycloaddition of sodium azide. The crystal structures of the homoleptic terpyridine–tetrazolate complexes [Ln(Li)₂]NHEt₃ (Ln=Nd, Eu, Tb for i=1, 2; Ln=Eu for i=3, 4) and of the monoaquo bypyridine–tetrazolate complex [Eu(H₂O)(L7)₂]NHEt₃ were determined. The tetradentate bipyridine–tetrazolate ligand forms nonhelical complexes that can contain a water molecule coordinated to the metal. Conversely, the pentadentate terpyridine–tetrazolate ligands wrap around the metal, thereby preventing solvent coordination and forming chiral double‐helical complexes similarly to the analogue terpyridine–carboxylate. Proton NMR spectroscopy studies show that the solid‐state structures of these complexes are retained in solution and indicate the kinetic stability of the hydrophobic complexes of terpyridine–tetrazolates. UV spectroscopy results suggest that terpyridine–tetrazolate complexes have a similar stability to their carboxylate analogues, which is sufficient for their isolation in aerobic conditions. The replacement of the carboxylate group with tetrazolate extends the absorption window of the corresponding terpyridine‐ (≈20 nm) and bipyridine‐based (25 nm) complexes towards the visible region (up to 440 nm). Moreover, the substitution of the terpyridine–tetrazolate system with different groups in the ligand series L3–L6 has a very important effect on both absorption spectra and luminescence efficiency of their lanthanide complexes. The tetrazole‐based ligands L1 and L3–L8 sensitize efficiently the luminescent emission of lanthanide ions in the visible and near‐IR regions with quantum yields ranging from 5 to 53 % for Eu^III complexes, 6 to 35 % for Tb^III complexes, and 0.1 to 0.3 % for Nd^III complexes, which is among the highest reported for a neodymium complex. The luminescence efficiency could be related to the energy of the ligand triplet states, which are strongly correlated to the ligand structures.     

N‐Heterocyclic Tridentate Aromatic Ligands Bound to [Ln(hexafluoroacetylacetonate)3] Units: Thermodynamic,Structural, and Luminescent Properties

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac^?) and neutral, semi‐rigid, tridentate 2,6‐bis(benzimidazol‐2‐yl)pyridine ligands ( Lk ) to trivalent lanthanide atoms (Ln^III). The solid‐state structures of [Ln( Lk )(hfac)₃] (Ln=La, Eu, Lu) showed that [Ln(hfac)₃] behaved as a neutral six‐coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron‐withdrawing trifluoromethyl substituents limited charge‐neutralization and favored cascade complexation with Lk ; 3) nine‐coordination was preserved for [Ln( Lk )(hfac)₃] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu( Lk )(hfac)₃], the ternary system Ln^III/hfac^?/ Lk is a promising candidate for the planned metal‐loading of preformed multi‐tridentate polymers.     

Hydrothermal Syntheses,Crystal Structures,and Luminescent Properties of Three Organic‐Lanthanide Complexes with 3‐Hydroxycinnamic Acid

Three new homodinuclear lanthanide(III) complexes [Ln₂(L)₆(2,2′‐bipy)₂] [Ln = Tb^III ( 1 ), Sm^III ( 2 ), Eu^III ( 3 ); HL = 3‐hydroxycinnamic acid (3‐HCA); 2,2′‐bipy = 2,2′‐bipyridine] were synthesized and characterized by IR spectroscopy, elemental analyses, and X‐ray diffraction techniques. Complexes 1 – 3 crystallize in triclinic system, space group P$\bar{1}$ . In all complexes the lanthanide ions are nine‐coordinate by two nitrogen atoms from the 2,2′‐bipy ligand and seven oxygen atoms from one chelating L ligands and four bridging L ligands, forming distorted tricapped trigonal prismatic arrangements. The lanthanide(III) ions are intramolecularly bridged by eight carboxylate oxygen atoms forming dimeric complexes with Ln ··· Ln distances of 3.92747(15), 3.9664(6), and 3.9415(4) Å for complexes 1 – 3 , respectively. The luminescent properties in the solid state of HL ligand and Eu^III complex are also discussed.     

Self‐Assembly versus Stepwise Synthesis: Heterometal–Organic Frameworks Based on Metalloligands with Tunable Luminescence Properties

A new family of heterometal–organic frameworks has been prepared by two synthesis strategies, in which IFMC‐26 and IFMC‐27 are constructed by self‐assembly and IFMC‐28 is obtained by stepwise synthesis based on the metalloligand (IFMC=Institute of Functional Material Chemistry). IFMC‐26 is a (3,6)‐connected net and IFMC‐27 is a (4,8)‐connected 3D framework. The metalloligands {Ni(H₄L)}(NO₃)₂ are connected by binuclear lanthanide clusters giving rise to a 2D sheet structure in IFMC‐28 . Notably, IFMC‐26‐Eu _x Tb _y and IFMC‐28‐Eu _x Tb _y have been obtained by changing the molar ratios of raw materials. Owing to the porosity of IFMC‐26 , Tb³⁺@IFMC‐26‐Eu and Eu³⁺@IFMC‐26‐Tb are obtained by postencapsulating Tb^III and Eu^III ions into the pores, respectively. Tunable luminescence in metal–organic frameworks is achieved by the two kinds of doping methods. In particular, the quantum yields of heterometal–organic frameworks are apparently enhanced by postencapsulation of Ln^III ions.     

Six‐Coordinate Lanthanide Complexes: Slow Relaxation of Magnetization in the Dysprosium(III) Complex

A series of six‐coordinate lanthanide complexes {(H₃O)[Ln(NA)₂]?H₂O}_n (H₂NA=5‐hydroxynicotinic acid; Ln=Gd^III ( 1?Gd ); Tb^III ( 2?Tb ); Dy^III ( 3?Dy ); Ho^III ( 4?Ho )) have been synthesized from aqueous solution and fully characterized. Slow relaxation of the magnetization was observed in 3?Dy . To suppress the quantum tunneling of the magnetization, 3?Dy diluted by diamagnetic Y^III ions was also synthesized and magnetically studied. Interesting butterfly‐like hysteresis loops and an enhanced energy barrier for the slow relaxation of magnetization were observed in diluted 3?Dy . The energy barrier (Δ_τ) and pre‐exponential factor (τ₀) of the diluted 3?Dy are 75 K and 4.21×10^?5 s, respectively. This work illustrates a successful way to obtain low‐coordination‐number lanthanide complexes by a framework approach to show single‐ion‐magnet‐like behavior.     

Synthesis,Structures, Luminescent and Magnetic Properties of Heterometallic 5p‐4f Compounds with Ethylenediaminetetra­acetate

A series of heterometallic Ln^III–Sb^III edta‐containing compounds with the formulas [Sb₂(edta)₂Ln]NO₃ · nH₂O [edta = ethylenediaminetetraacetate; Ln = Eu, n = 7 ( 1 ); Gd, n = 7.5 ( 2 ) and Tb, n = 8 ( 3 )] were synthesized and characterized by elemental analyses (EA), powder X‐ray diffraction (PXDP), Fourier transform infrared spectroscopy (FT‐IR), and thermogravimetric analyses (TGA). Their fluorescence and magnetic properties were also studied. The thermal analysis demonstrates the compounds formation of the antimony, lanthanide ions, and edta^4– ligands. FT‐IR spectra reveal that the antimony and lanthanide ions are connected through the carboxylate bridges. The studies of luminescence properties show that compounds 1 and 3 exhibit typical luminescence in the visible region. Furthermore, magnetic properties reveal compounds 2 and 3 have weak ferromagnetic behavior.     

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 L₃‐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 9 O for early lanthanides to 8 O 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.     

Synthesis,Structure, and Magnetic Properties of a Series of Dinuclear Lanthanide Complexes Assembled by Acetate and a Schiff Base Ligand

Five dinuclear lanthanide complexes [Ln₂L₂(NO₃)₂(OAc)₄] · 2CH₃CN [Ln = Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ), and Er ( 5 )] [L = 2‐((2‐pyridinylmethylene)hydrazine)ethanol] were synthesized from the reactions of Ln(NO₃)₃ · 6H₂O with L and CH₃COOH in the presence of triethylamine. Their crystal structures were determined. They show similar dinuclear cores with the two lanthanide ions bridged by four acetate ligands in the μ₂‐η¹:η² and μ₂‐η¹:η¹ bridging modes. Each Ln^III ion in complexes 1 – 5 is further chelated by one L ligand and one nitrate ion, leading to the formation of a nine‐coordinated mono‐capped square antiprism arrangement. The dinuclear molecules in 1 – 5 are consolidated by hydrogen bonds and π ··· π stacking interactions to build a two‐dimensional sheet. Their magnetic properties were investigated. It revealed antiferromagnetic interactions between the Gd^III ions in 1 and ferromagnetic interactions between the Tb^III ions in 2 . The profiles of χ_mT vs. T curves of 3 – 5 reveal that the magnetic properties of 3 – 5 are probably dominated by the thermal depopulation of the Stark sublevels of Ln^III ions.     

The Series of Rare Earth Complexes [Ln2Cl6(μ‐4,4′‐bipy)(py)6], Ln=Y,Pr, Nd,Sm‐Yb: A Molecular Model System for Luminescence Properties in MOFs Based on LnCl3 and 4,4′‐Bipyridine

A series of 12 dinuclear complexes [Ln₂Cl₆(μ‐4,4′‐bipy)(py)₆], Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, ( 1 – 12 , respectively) was synthesized by an anhydrous solvothermal reaction in pyridine. The complexes contain a 4,4′‐bipyridine bridge and exhibit a coordination sphere closely related to luminescent lanthanide MOFs based on LnCl₃ and 4,4‐bipyridine. The dinuclear complexes therefore function as a molecular model system to provide a better understanding of the luminescence mechanisms in the Ln‐N‐MOFs ${\hbox{}{{\hfill 2\atop \hfill \infty }}}$ [Ln₂Cl₆(4,4′‐bipy)₃] ? 2(4,4′‐bipy). Accordingly, the luminescence properties of the complexes with Ln=Y, Sm, Eu, Gd, Tb, Dy, ( 1 , 4 – 8 ) were determined, showing an antenna effect through a ligand–metal energy transfer. The highest efficiency of luminescence is observed for the terbium‐based compound 7 displaying a high quantum yield (QY of 86 %). Excitation with UV light reveals typical emission colors of lanthanide‐dependent intra 4f–4f‐transition emissions in the visible range (Tb^III: green, Eu^III: red, Sm^III: salmon red, Dy^III: yellow). For the Gd^III‐ and Y^III‐containing compounds 6 and 1 , blue emission based on triplet phosphorescence is observed. Furthermore, ligand‐to‐metal charge‐transfer (LMCT) states, based on the interaction of Cl^? with Eu^III, were observed for the Eu^III compound 5 including energy‐transfer processes to the Eu^III ion. Altogether, the model complexes give further insights into the luminescence of the related MOFs, for example, rationalization of Ln‐independent quantum yields in the related MOFs.     

Three Phenoxo‐Bridged Dinuclear Lanthanide Complexes: Syntheses,Crystal Structures,and Magnetic Properties

Three dinuclear lanthanide complexes [Ln₂(H₂L)₂(NO₃)₄] [Ln = Dy ( 1 ), Tb ( 2 ), and Gd ( 3 )] [H₃L = 2‐hydroxyimino‐N′‐[(2‐hydroxy‐3‐methoxyphenyl)methylidene]‐propanohydrazone] were solvothermally synthesized by varying differently anisotropic rare earth ions. Single‐crystal structural analyses demonstrate that all the three complexes are crystallographically isostructural with two centrosymmetric Ln^III ions aggregated by a pair of monodeprotonated H₂L^– anions. Weak intramolecular antiferromagnetic interactions with different strength were mediated by a pair of phenoxo bridges due to superexchange and/or single‐ion anisotropy. Additionally, the Dy^III‐based entity shows the strongest anisotropy exhibits field‐induced single‐molecule magnetic behavior with two thermally activated relaxation processes. In contrast, 3 with isotropic Gd^III ion has a significant cryogenic magnetocaloric effect with the maximum entropy change of 25.7 J · kg^–1 · K^–1 at 2.0 K and 70.0 kOe.     

Syntheses,Structures, and Properties of the 3D Lanthanide Organic Frameworks with N‐Heterocyclic Polycarboxylic Acids

Four 3D lanthanide organic frameworks from potassium pyrazine‐2, 3, 5, 6‐tetracarboxylate (K₄pztc) or potassium pyridine‐2, 3, 5, 6‐tetracarboxylate (K₄pdtc), namely, {[KEu(pztc)(H₂O)₂] · H₂O}_n ( 1 ), {[KTb(pztc)(H₂O)₂] · 1.25H₂O}_n ( 2 ), {[KLn(pdtc)(H₂O)] · H₂O}_n [Ln = Gd ( 3 ), Ho ( 4 )], were synthesized by reaction of the corresponding lanthanide oxides with K₄pztc or K₄pdtc in presence of HCl under hydrothermal conditions, and characterized by elemental analysis, TGA, IR and fluorescence spectroscopy as well as X‐ray diffraction. In complexes 1 and 2 , the dodecadentate chelator pztc^4– links four Ln^III ions and four K^I ions. The coordination mode of the pztc^4– ligand is reported for the first time herein. Complexes 3 and 4 are isostructural with earlier reported Nd, Dy, Er complexes. Moreover, the Eu^III and Tb^III complexes exhibit the characteristic luminescence.     

Synthesis, structure, and magnetic properties of heterometallic trinuclear complexes {MII��LnIII��MII} (MII = Ni, Cu; LnIII = La, Pr, Sm, Eu, Gd)

Trinuclear heterometallic complexes containing the {M₂Ln(Piv)₆(NO₃)} (M^II = Ni, Cu; Ln^III = Nd, Pr, Sm, Eu, Gd; Piv^? is the anion of pivalic acid) and {Cu₂Ln(Piv)₈)]^? (Ln^III = Eu, Gd) metal cores were synthesized, their structures and magnetic properties were studied. For the most compounds, it was shown that their magnetic properties can be interpreted taking no interaction of the 3d-metal ions and a lanthanide into account. Ferromagnetic exchange interactions were found to exist between the unpaired electrons of the paramagnetic centers in the exchange clusters of the gadolinium-containing heterometallic complexes {M-Gd-M} (M = Ni or Cu).     

Lanthanide(III) Complexes of Bis‐semicarbazone and Bis‐imine‐Substituted Phenanthroline Ligands: Solid‐State Structures,Photophysical Properties,and Anion Sensing

Phenanthroline‐based hexadentate ligands L¹ and L² bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as La^III, Eu^III, Tb^III, Lu^III, and Y^III metal ions, were synthesized, and the crystal structures of [ML¹Cl₃] (M=La^III, Eu^III, Tb^III, Lu^III, or Y^III) complexes were determined. Solvent or water molecules act as coligands for the rare‐earth metals in addition to halide anions. The big Ln^III ion exhibits a coordination number (CN) of 10, whereas the corresponding Eu^III, Tb^III, Lu^III, and Y^III centers with smaller ionic radii show CN=9. Complexes of L², namely [ML²Cl₃] (M=Eu^III, Tb^III, Lu^III, or Y^III) ions could also be prepared. Only the complex of Eu^III showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine‐5′‐triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine‐5′‐diphosphate (ADP) and adenosine‐5′‐monophosphate (AMP) was found. ³¹P NMR spectroscopic studies revealed the formation of a [EuL²(ATP)] coordination species.     

Mono and trinuclear lanthanide complexes of 13-membered tetraaza macrocycle: Synthesis and characterization

The reaction of 1,8-diamino-3,6-diazaoctane and diethyl malonate in dry methanol yielded a 13-membered macrocycle. Complexes of the type [Ln(tatd)Cl₂ (H₂O)₃]Cl [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy; tatd=1, 5, 8, 11-tetra-azacyclotridecane-2,4-dione] have been synthesized by template condensation. The complex [La(tatd)Cl₂ (H₂O)₃]Cl in methanol was reacted with lanthanide chlorides to yield the trinuclear complexes of type [2{La(tatd)Cl₂(H₂O)₃}LnCl₃]Cl₂ [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy]. The chemical compositions of mono and trinuclear complexes have been established on the basis of analytical, molar conductance, electrospray (ES) and fast atom bombardment (FAB) mass data. In mononuclear complexes the Ln³⁺ ion is encapsulated by four ring nitrogens and in trimetallic complexes the exo-carbonyl oxygens of two mononuclear units coordinate to the Ln³⁺ ions resulting in a polyhedron around the lanthanide ions. Thus the macrocycle is bonded in a tetradentate fashion in the former complexes and hexadentate in the latter. The coordination number nine around the encapsulated Ln³⁺ and seven around the exo-oxygen bonded Ln³⁺ ions are established. The symmetry of the ligand field around the metal ions is indicated from the emission spectra.     

Cationic lanthanide monoporphyrinates with Sm, Eu, Gd and Tb, synthesis and spectroscopic properties in aqueous and non-aqueous media

The synthesis of a new series of cationic monoporphyrinates with “light” lanthanide ions is reported. The meso-tetrakis(4-pyridyl)porphyrin, (tpyp)H₂, was used as the tetrapyrrole ligand, and the metallation reaction with the lanthanide ions in acetyl-acetonato form, leading to Ln(tpyp)acac, where Ln = Sm, Eu, Gd and Tb, was carried out. The cationic monoporphyrinates, Ln(tmepyp)acac, were synthesized via the corresponding Ln(tpyp)acac. These complexes are freely soluble in aqueous and non-aqueous solutions, like MeOH, H₂O or N,N-dimethylformamide. Their spectroscopic properties in water and DMF solutions are reported. All the complexes were characterized on the basis of their UV-vis, IR and ESR data. No ESR spectra were obtained for cationic porphyrins in DMF for Sm, Eu and Tb, while the spectra of Gd(tmepyp)acac in DMF exhibits smaller ΔH_pp (103.1 G) among the spectra of Gd^III complexes. The unexpected broad signal of Eu(t-mepyp)acac, ΔH_pp = 126.9 G, in H₂O is discussed in terms of the formal oxidation state +2 for the central ion.     

Highly Luminescent,Water‐Soluble Lanthanide Fluorobenzoates: Syntheses,Structures and Photophysics,Part I: Lanthanide Pentafluorobenzoates

Highly luminescent, photostable, and soluble lanthanide pentafluorobenzoates have been synthesized and thoroughly characterized, with a focus on Eu^III and Tb^III complexes as visible emitters and Nd^III, Er^III, and Yb^III complexes as infrared emitters. Investigation of the crystal structures of the complexes in powder form and as single crystals by using X‐ray diffraction revealed five different structural types, including monomeric, dimeric, and polymeric. The local structure in different solutions was studied by using X‐ray absorption spectroscopy. The photoluminescence quantum yields (PLQYs) of terbium and europium complexes were 39 and 15 %, respectively; the latter value was increased almost twice by using the heterometallic complex [Tb_0.5Eu_0.5(pfb)₃(H₂O)] (Hpfb=pentafluorobenzoic acid). Due to the effectively utilized sensitization strategy (pfb)^?→Tb→Eu, a pure europium luminescence with a PLQY of 29 % was achieved.     

2,2′‐Bipyrimidine as Efficient Sensitizer of the Solid‐State Luminescence of Lanthanide and Uranyl Ions from Visible to Near‐Infrared

Treatment of Ln(NO₃)₃?nH₂O with 1 or 2 equiv 2,2′‐bipyrimidine (BPM) in dry THF readily afforded the monometallic complexes [Ln(NO₃)₃(bpm)₂] (Ln=Eu, Gd, Dy, Tm) or [Ln(NO₃)₃(bpm)₂]?THF (Ln=Eu, Tb, Er, Yb) after recrystallization from MeOH or THF, respectively. Reactions with nitrate salts of the larger lanthanide ions (Ln=Ce, Nd, Sm) yielded one of two distinct monometallic complexes, depending on the recrystallization solvent: [Ln(NO₃)₃(bpm)₂]?THF (Ln=Nd, Sm) from THF, or [Ln(NO₃)₃(bpm)(MeOH)₂]?MeOH (Ln=Ce, Nd, Sm) from MeOH. Treatment of UO₂(NO₃)₂?6H₂O with 1 equiv BPM in THF afforded the monoadduct [UO₂(NO₃)₂(bpm)] after recrystallization from MeOH. The complexes were characterized by their crystal structure. Solid‐state luminescence measurements on these monometallic complexes showed that BPM is an efficient sensitizer of the luminescence of both the lanthanide and the uranyl ions emitting visible light, as well as of the Yb^III ion emitting in the near‐IR. For Tb, Dy, Eu, and Yb complexes, energy transfer was quite efficient, resulting in quantum yields of 80.0, 5.1, 70.0, and 0.8 %, respectively. All these complexes in the solid state were stable in air.