Small Cyclic Diglycolamides: Tautomerism, Solvent Extraction and Coordination with f-Elements: One Strain to Rule Them All.

The search for new effective extractants is an important task for the management of high-level liquid waste (HLW) generated during the reprocessing of spent nuclear fuel. Here, we synthesized a series of diglycolamides with cyclic substituents for the first time. We disclosed their coordination with f-element nitrates [La(NO3)3 and UO2(NO3)2] by SC-XRD study and complexation properties toward Am(III), Ln(III), and U(VI) during solvent extraction from nitric acid solutions. Using dynamic nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations, the importance of tautomerism in the extraction properties of diglycolamides was shown.

Pyridine Diphosphonate Ligand for Stabilization of Tetravalent Uranium and Neptunium in Aqueous Medium under Aerobic Conditions.

Though uranium is usually present in its +6 oxidation state (as uranyl ion) in aqueous solutions, its conversion to oxidation states such as +4 or +5 is a challenging task. Electrochemical reduction and axial oxo activation are the preferred methods to get stable unusual oxidation states of uranium in an aqueous medium. In previous studies, dicarboxylic acid has been used to stabilize UO2+ in aqueous alkaline solutions. In the present work, a diphosphonate ligand was chosen due to its higher complexing ability compared to that of the carboxylate ligands. Neptunium complexation studies with 2,6-pyridinediphosphonic acid (PyPOH) indicated the formation of different species at different pH values and the complexation facilitates disproportionation of NpO2+ to Np4+ and NpO22+ at pH 2. Hexavalent actinides form insoluble complexes in aqueous media at pH = 2, as confirmed by UO22+ complexation studies. The in situ complexation-driven precipitation resulted in conversion to pure Np4+ in aqueous media as the Np4+-PyPOH complex. A strong complexing ability of the PyPOH ligand toward the Np4+ ion is also seen for the stabilization of the electrochemically generated U4+ in aqueous medium under aerobic conditions. The U4+-PyPOH complex was found to be stable for 3 months. Raman, UV-vis, fluorescence, and cyclic voltametric studies along with density functional theory (DFT) calculations were done to get structural insights into the PyPOH complexes of actinides in different oxidation states.

Kinetic features of solvent extraction by N,O-donor ligands of f-elements: a comparative study of diamides based on 1,10-phenanthroline and 2,2'-bipyridine.

A variant of microfluidic setup design for the study of extraction kinetics has been proposed. Mass transfer constants for Am(III) and Eu(III) and observed rate constants were obtained for N-,O-donor ligands featuring phenanthroline and bipyridyl cores. The possibility of determining rate constants for cations independently of each other makes it possible to observe the kinetic effect of separation. The extraction rate was found to be lower for the bipyridyl ligand, compared to phenanthroline. The values of the rotation barriers for the ligands were calculated using the DFT method. The values correlate with the obtained low extraction rate for the bipyridyl ligand. Also, crystallographic data showing anti-conformation for the bipyridyl ligand align with the kinetic data. Surface tension was also determined for the systems with the studied ligands. It is shown that at equal ligand concentrations, the value of surface tension agrees with the extraction rate. Furthermore, it is shown that for the bipyridyl ligand, prior contact of the organic phase with nitric acid significantly affects the surface tension.

Intramolecular Re···O Nonvalent Interactions as a Stabilizer of the Polyoxorhenate(VII).

The first polyoxorhenate(VII) compound, pyrazolium polyoxorhenate ((C4N2H5)2Re4O15), and two new rhenium(VII) and technetium(VII) salts have been synthesized and studied. The structure of Tc2O7 has been reinvestigated. The [Re4O15]2- polyoxoanion contains four Re(VII) atoms: one with an octahedral environment and three with a tetrahedral environment. Polyoxorhenate is formed in the presence of a buffering agent, pyrazole, the latter maintaining pH = 2.5 during the formation of crystals. The [Re4O15]2- polyoxoanion has novel stoichiometry and the cis-conformation, likely due to the stabilizing intramolecular nonvalence interactions. For the first time, intramolecular interactions of the Re···O, Re···µ-O, and O···O are described (previously known were only intermolecular ones). In all of the compounds, intermolecular Re···O interactions are observed, which, however, in other compounds, do not lead to the formation of polyoxometalates. The Hirshfeld surface analysis showed that the main contribution to intermolecular interactions is made by the O···H/H···O contacts, van der Waals interactions of the H···H for cations, and the O···O for anions. DFT calculations of the [Re4O15]2- geometry, compared with the crystallographic data, revealed a deviation in the angles. Mass spectroscopy of the red polyoxometalate [Tc20O68]4- was carried out for the first time. Comparison of the results of MALDI and LI for the first known polyoxometalates of the manganese subgroup made it possible to find general patterns of oligomerization for rhenium and technetium compounds. The ESI-MS and LI-MS methods applied to solution and crystals Re compounds made it possible to prove rhenium being able to form not only [Re4O15]2- but also heavier polyoxoanions.

Solvent Extraction and Conformation Rigidity: Actinide(IV) and Actinide(VI) Come Together.

The first comprehensive structural and extraction study of a 2,2'-bipyridine-6,6'-dicarboxamide (L diamide) extractant for U, Np, Pu, Th, Am, and Eu ions showed great potential for actinide separation due to steric hindrance of the amidic side phenyl ring of the given compound. The study of the complexes of An(VI) and Th(IV) with 2,2'-bipyridyldicarboxamide-type extractants demonstrated the structure of the extraction species for the first time. Investigation of the extraction properties with the radiometric and millimolar quantities of actinides showed similar extraction trends. For the first time, a metal-ion-induced phenyl-ring rotation restriction was found for the U, Th, and Eu complexes by employing temperature-dependent dynamic NMR. A study of the solution behavior of the complexes accompanied by density functional theory modeling studies elucidated the mechanism of the unusual C-N bond rotation restriction induced by metal coordination.

Comparative Investigation into the Complexation and Extraction Properties of Tridentate and Tetradentate Phosphine Oxide-Functionalized 1,10-Phenanthroline Ligands toward Lanthanides and Actinides.

Two new phosphine oxide-functionalized 1,10-phenanthroline ligands, tetradentate 2,9-bis(butylphenylphosphine oxide)-1,10-phenanthroline (BuPh-BPPhen, L1 ) and tridentate 2-(butylphenylphosphine oxide)-1,10-phenanthroline (BuPh-MPPhen, L2 ), were synthesized and studied comparatively for their coordination with trivalent actinides and lanthanides. The complexation mechanisms of these two ligands toward trivalent f-block elements were thoroughly elucidated by NMR spectroscopy, UV/vis spectrophotometry, fluorescence spectrometry, single-crystal X-ray diffraction, solvent extraction, and theoretical calculation methods. NMR titration results demonstrated that 1 : 1 and 1 : 2 (metal to ligand) lanthanides complexes formed for L1 , whereas 1 : 1, 1 : 2 and 1 : 3 lanthanide complexes formed for L2 in methanol. The formation of these species was validated by fluorescence spectrometry, and the corresponding stability constants for the complexes of NdIII with L1 and L2 were determined by using UV/vis spectrophotometry. Structures of the 10-coordinated 1 : 1-type complexes of EuL1 (NO3 )3 and [EuL2 (NO3 )3 (H2 O)] Et2 O in the solid state were characterized by X-ray crystallography. In solvent-extraction experiments, L1 exhibited extremely strong extraction ability for both AmIII and EuIII , whereas L2 showed nearly no extraction toward AmIII or EuIII due to its high hydrophilicity. Finally, the structures and bonding natures of the complex species formed between AmIII /EuIII and L1 /L2 were analyzed in DFT calculations.

Influence of a N-Heterocyclic Core on the Binding Capability of N,O-Hybrid Diamide Ligands toward Trivalent Lanthanides and Actinides.

N,O-hybrid diamide ligands with N-heterocyclic skeletons are one of the promising extractants for the selective separation of actinides over lanthanides in a highly acidic HNO3 solution. In this work, three hard-soft donor mixed diamide ligands, pyridine-2,6-diylbis(pyrrolidin-1-ylmethanone) (Pyr-PyDA), 2,2'-bipyridine-6,6'-diylbis(pyr-rolidine-1-ylmethanone) (Pyr-BPyDA), and (1,10-phenanthroline-2,9-diyl)bis(pyrrolidin-1-ylmethanone) (Pyr-DAPhen), were synthesized and used to probe the influence of N-heterocyclic cores on the complexation and extraction behaviors with trivalent lanthanides and actinides. 1H NMR titration experiments demonstrated that 1:1 metal-to-ligand complexes were mainly formed between the three ligands and lanthanides, but 1:2 type complexes were also formed between tridentate Pyr-PyDA and Lu(III). The stability constants (log ß) of these three ligands with two typical lanthanides, Nd(III) and Eu(III), were determined through spectrophotometric titration. It is found that Pyr-DAPhen formed the most stable complexes, while Pyr-PyDA formed the most unstable complexes with lanthanides, which coincided well with the following solvent extraction results. The solid-state structures of 1:1 type complexes of these three ligands with La(III), Nd(III), and Er(III) in nitrate media were identified by a single-crystal X-ray diffraction technique. Nd(III) and Er(III) were 10-coordinated with Pyr-PyDA, Pyr-BPyDA, and Pyr-DAPhen via one ligand molecule and three nitrate ions. La(III), because of its larger ionic radius, was 11-coordinated with Pyr-DAPhen through one ligand molecule, three nitrate ions, and one methanol molecule. Solvent extraction experiments showed that the preorganized phenanthroline-derived Pyr-DAPhen had the best extraction performance for trivalent actinide among the three ligands tested. This work provides some experimental insights into the design of more efficient ligands for trivalent actinide separation by adjusting the N-heterocyclic cores.

Way to Enforce Selectivity via Steric Hindrance: Improvement of Am(III)/Eu(III) Solvent Extraction by Loaded Diphosphonic Acid Esters.

Hybrid donor extractants are a promising class of compounds for the separation of trivalent actinides and lanthanides. Here, we investigated a series of sterically loaded diphosphonate ligands based on bipyridine (BiPy-PO-iPr and BiPy-PO-cHex) and phenanthroline (Phen-PO-iPr and Phen-PO-cHex). We studied their complex formation with nitrates of trivalent f-elements in solvent extraction systems (Am and Eu) and homogeneous acetonitrile solutions (Nd, Eu, and Lu). Phenanthroline extractants demonstrated the highest efficiency and selectivity [SF(Am/Eu) up to 14] toward Am(III) extraction from nitric acid solutions among all of the studied diphosphonates of N-heterocycles. The binding constants established by UV-vis titration also indicated stronger binding of sterically impaired diphosphonates compared to the primary substituted diphosphonates. NMR titration and slope analysis during solvent extraction showed the formation of 2:1 complexes at high concentrations (>10-3 mol/L) for phenanthroline-based ligands. According to UV-vis titrations at low concentrations (10-5-10-6 mol/L), the phenanthroline-based ligands formed 1:1 complexes. Bipyridine-based ligands formed 1:1 complexes regardless of the ligand concentration. Luminescence titrations revealed that the quantum yields of the complexes with Eu(III) were 81 ± 8% (BiPy-PO-iPr) and 93 ± 9% (Phen-PO-iPr). Single crystals of the structures [Lu(µ2,κ4-(iPrO)2P(O)Phen(O)2(OiPr))(NO3)2]2 and Eu(Phen-PO-iPr)(NO3)3 were obtained by chemical synthesis with the Phen-PO-iPr ligand. X-ray diffraction studies revealed a closer contact of the f-element with the aromatic N atoms in the case of sterically loaded P═O ligands compared with sterically deficient ligands. Density functional theory calculations allowed us to rationalize the observed selectivity trends in terms of the bond length, Mayer bond order, and preorganization energy.

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.

Bipyridyldicarboxamides and f-metals: the influence of electron effects on the structure, stability, separation, and photophysical properties of their complexes.

In this work, three isomeric fluorinated bipyridyldicarboxamides were studied to evaluate the impact of the fluorine atom position on the structure, stability, Am(III)/Ln(III) separation, and photophysical properties of their complexes. The complexes of the fluorinated amides have a metal-to-ligand composition of 1 : 1, which is independent of the fluorine atom position or lanthanide metal. The bipyridyl fragments in the fluorinated complexes are flattened compared with those in unsubstituted ones. Ln-to-heteroatom distances are more affected by steric hindrance in the ligand and further by lanthanide ion radius contraction. This leads to significant effectivity of heavy lanthanide extraction compared with the light ones, particularly for 4F diamide. Fluorination leads to a slight variation in the excited triplet state of the complexes, and hence, the effectiveness of luminescence increases for Eu, Sm, and Tb complexes. Moreover, fluorination significantly affects the CIE chromaticity coordinates for the complexes.

Sensing and extraction of hazardous metals by di-phosphonates of heterocycles: a combined experimental and theoretical study.

In this study, pyridine and phenanthroline diphosphonate ligands were investigated for the first time from the context of solvent extraction and potentiometric sensing of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) cations. The extraction efficiency under the same conditions for phenanthroline-diphosphonates is considerably higher than that for pyridine ligands. At the same time, the pyridine-diphosphonates show pronounced selectivity towards lead in this metal series. The extraction systems with phenanthroline diphosphonates provided the most efficient extraction of Cd(II) and Pb(II) cations (D > 90). The newly developed pyridine and phenanthroline diphosphonate ligands have proven to be highly effective components in plasticized polymeric membranes. These ligands can be utilized to construct potentiometric ion sensors that exhibit a notable response specifically towards Pb(II) cations. Among the previously reported tetradentate ligands, the phenanthroline diphosphonate ligand, when incorporated into plasticized polymeric membranes, demonstrated the highest sensitivity towards d-metals and Pb(II). The structure of the single crystal complex of Pb(II) and Cd(II) with pyridine-diphosphonates was studied by X-ray diffraction analysis (XRD). The geometry of Cu(II), Zn(II), Cd(II) and Pb(II) complexes and the energy effect of the complex formation, including pseudo-oligomerization reactions, were determined by DFT calculations. The high sensing and extraction efficiency of diphosphonates with respect to Pb(II) is consistent with the minimum values of complex formation energies. The variation in sensory and extraction properties observed among the studied diphosphonate ligands is influenced by the ability to form polynuclear complexes with Pb(II) cations, whereas such properties are absent in the case of Cd(II) cations.

Sandwich double-decker lanthanide(III) "intracavity" complexes based on clamshell-type phthalocyanine ligands: synthesis, spectral, electrochemical, and spectroelectrochemical investigations.

Phthalocyanine compounds of novel type based on a bridged bis-ligand, denoted "intracavity" complexes, have been prepared. Complexation of clamshell ligand 1,1'-[benzene-1,2-diylbis(methanediyloxy)]bis[9(10),16(17),23(24)-tri-tert-butylphthalocyanine] ((clam,tBu)Pc(2)H(4), 1) with lanthanide(III) salts [Ln(acac)(3)]⋅n H(2)O (Ln = Eu, Dy, Lu; acetylacetonate) led to formation of double-deckers (clam,tBu)Pc(2)Ln (2 a-c). Formation of high molecular weight oligophthalocyanine complexes was demonstrated as well. The presence of an intramolecular covalent bridge affecting the relative arrangement of macrocycles was shown to result in specific physicochemical properties. A combination of UV/Vis/NIR and NMR spectroscopy, MALDI-TOF mass-spectrometry, cyclic voltammetry, and spectroelectrochemistry provided unambiguous characterization of the freshly prepared bis-phthalocyanines, and also revealed intrinsic peculiarities in the structure-property relationship, which were supported by theoretical calculations. Unexpected NMR activity of the paramagnetic dysprosium complex 2 b in the neutral π-radical form was observed and examined as well.

Pyridine-di-phosphonates as chelators for trivalent f-elements: kinetics, thermodynamic and interfacial study of Am(III)/Eu(III) solvent extraction.

The fractionation of high-level radioactive waste from nuclear power plants simplifies the handling of its components, and facilitates the reduction of radiotoxic effects on the environment. The search and study of new ligands for solvent extraction, as one of the methods in fractionation, remains a complex and important research task. In this work, four pyridine diphosphonate ligands were synthesized. These ligands are part of the class of the N,O-donor extractants, which are selective towards Am(III). The separation factor SF(Am/Eu) for the best extractant reached values up to 10. The influence of the substituents on the efficiency of extraction and complexation of trivalent f-elements, the kinetics of extraction, and the behavior of the ligand at the interface were described. The effect of nitric acid concentration on the extraction was shown. The stoichiometry of the complexes was determined by slope analysis in solvent extraction experiment and verified by spectrophotometric titration in acetonitrile. Liquid tension experiments with a pendant drop method revealed the interfacial properties of the ligands in "F-3 solvent/H2O" and "F-3 solvent/HNO3" systems. The relationship between the surface activity and the ligand structure was shown. Studies of the extraction kinetics were performed in a modified Lewis cell. The effect of the ligand structure on the extraction rate was shown. The DFT calculation with the B3LYP density functional was used to explain the extraction properties of the ligands, including selectivity. The calculation of the pre-organization energy of the ligands explained the kinetics and extraction patterns for the studied series.

Novel cis-Pt(II) Complexes with Alkylpyrazole Ligands: Synthesis, Characterization, and Unusual Mode of Anticancer Action.

One concept of improving anticancer effects of conventional platinum-based antitumor drugs consists of conjugating these compounds with other biologically (antitumor) active agents, acting by a different mechanism. Here, we present synthesis, physicochemical characterization, biological effects, and mechanisms of action of four new analogs of conventional cisplatin, namely, cis-Pt(II) complexes containing either methyl or ethyl pyrazole N-donor ligands and chlorido or iodido ligands. It is noteworthy that while chlorido complexes display activity in a variety of cancer cell lines comparable to cisplatin, iodido complexes are considerably more potent due to their enhanced hydrophobicity and consequently enhanced cellular accumulation. Moreover, all of the studied Pt(II) alkylpyrazole complexes display a higher selectivity for tumor cells and effectively overcome the acquired resistance to cisplatin. Further results focused on the mechanism of action of the studied complexes and showed that in contrast to cisplatin and several platinum-based antitumor drugs, DNA damage by the investigated Pt(II)-alkylpyrazole complexes does not play a major role in their mechanism of action. Our findings demonstrate that inhibition of the tubulin kinesin Eg5, which is essential for forming a functional mitotic spindle, plays an important role in their mechanism of antiproliferative action.

Diamidophosphites from ß-hydroxyamides: readily assembled ligands for Pd-catalyzed asymmetric allylic substitution.

Two groups of modular chiral diamidophosphite ligands were easily synthesised from accessible N-Boc-amino alcohols and pseudodipeptides. The reaction of these compounds with [Pd(allyl)Cl]2 in the presence of AgBF4 yielded complexes [Pd(allyl)(L)2]BF4. In addition, metallochelates [Pd(allyl)(L)]BF4 with (S)-methioninol-based P,S-bidentate ligands were prepared. The structures of the novel ligands and complexes were elucidated by means of 2D-NMR and were confirmed by single-crystal X-ray diffraction, as well as by DFT calculations. Asymmetric inducers of this type exhibited high enantioselectivities in the Pd-mediated allylic substitution of (E)-1,3-diphenylallyl ethyl carbonate with CH2(CO2Me)2 (up to 98% ee) and (CH2)4NH (up to 92% ee). Ee values of up to 86% and 73% were obtained in the Pd-catalyzed allylic alkylation of cinnamyl acetate with ethyl 2-oxocyclohexane-1-carboxylate and ethyl 2-oxocyclopentane-1-carboxylate, respectively. The effects of the structural modules, such as the nature of the phosphorus-containing ring or exocyclic substituent, on the catalytic activity and enantioselectivity were investigated.

The Fischer-Tropsch reaction in the aqueous phase over rhodium catalysts: a promising route to selective synthesis and separation of oxygenates and hydrocarbons.

In the present communication, we uncovered the aqueous phase Fischer-Tropsch reaction over rhodium catalysts. The reaction results in the synthesis and consecutive separation of hydrocarbons and oxygenates into two phases. Use of a rhodium Schiff base complex as a precursor for catalyst preparation allows efficient control of the Rh metal nanoparticle size distribution and leads to higher alcohol selectivity.

Unfolding the complexation and extraction of Am3+ and Eu3+ using N-heterocyclic aromatic diphosphonic acids: a combined experimental and DFT study.

Phosphonate based ligands are well known for the extraction of 'f' block elements. Three N,O-donor N-heterocyclic aromatic diphosphonate ligands were evaluated in the present work for the extraction/separation studies of Am3+ and Eu3+. Complexation studies in aqueous medium using luminescence titration indicated the formation of anionic complexes in the case of Eu3+. Two phase liquid-liquid extraction studies were, therefore, carried out by employing Aliquat-336 as the liquid anion exchanger. The results indicated the formation of a species with a metal-ligand stoichiometry of 1 : 3 in the case of pyridine-2,6-diphosphonic acid (PyPOH). In the case of 2,2'-bipyridine-6,6'-diphosphonic acid (BipyPOH), however, a 1 : 2 complex was extracted and 1,10-phenanthroline-2,9-diphosphonic acid (PhenPOH) extracts the Am3+ and Eu3+ ions by forming both 1 : 2 and 1 : 3 complexes. Formation of these kinds of anionic complexes was further confirmed using electrospray ionization mass spectrometry (ESI-MS). DFT calculations predicted the structure of the anionic complexes. The non-selectivity of these kinds of ligands between Am3+ and Eu3+ was attributed to the presence of unfavorable covalent interactions in the metal-ligand bonds.

Sandwich double-decker Er(iii) and Yb(iii) complexes containing naphthalocyanine moiety: synthesis and investigation of the effect of a paramagnetic metal center.

Novel heteroleptic Er(iii) and Yb(iii) naphthalocyaninato-phthalocyaninates containing an octa-phenyl or octa-phenoxysubstituted naphthalocyanine deck were synthesised and identified by 1H NMR, EPR and high resolution MALDI-TOF/TOF mass spectrometry. Direct synthesis of novel homoleptic Yb(iii) bis (octa-phenylnaphthalocyaninate) was carried out. Downfield lanthanide induced shifts of the aromatic protons in target compounds were observed compared with the corresponding diamagnetic Lu(iii) complexes. In the near-IR absorption spectra, an increase in ionic radius from Lu(iii) to Er(iii) resulted in a bathochromic shift of the intervalence band up to 1473 nm. This work presents the first experimental EPR study of Yb(iii) bis naphthalocyaninate, where a set of magnetic parameters and properties (including spin, magnitude and sign of magnetic anisotropy parameter D, increased splitting in a crystal field, ferromagnetic f-π interaction etc.) were determined and interpreted by both EPR and SQUID techniques and supported by theoretical considerations.

The lanthanide complexes of 2,2'-bipyridyl-6,6'-dicarboxylic dimethylanilides: the influence of a secondary coordination sphere on the stability, structure, luminescence and f-element extraction.

Four of the six possible isomeric 2,2'-bipyridyl-6,6'-dicarboxylic dimethylanilides were studied from the point of view of the impact of a secondary coordination sphere on the formation of complexes with lanthanides in solution, as well as the crystal structure and photophysical properties of the complexes. All ligands form complexes with a 1 : 1 metal-to-ligand ratio with an lg ß1 in the range of 6.0-8.8, and strong correlations between secondary coordination sphere modulation and stability of the complexes within the lanthanide series. Although substitution at the o-position of the aromatic ring leads to significant elongation of M-OL bonds in a crystal, this significantly affects the stability of the complexes. The luminescence of the complexes is the most effective for europium complexes. From luminescence measurements of gadolinium complexes, the triplet energy levels of ligands were located as follows: o-methylated ligands show 10% higher levels than other isomers. Also, o-methylation of the phenyl ring increases the lifetime value while m-methylation reduces this value.

Hard-and-soft phosphinoxide receptors for f-element binding: structure and photophysical properties of europium(iii) complexes.

New phosphinoyl-containing tetradentate heterocycles preorganised for metal ion binding were designed and prepared in high yields. The X-ray structures of two allied phosphinoyl-bearing 2,2'-bipyridyl and phenanthroline ligands, as well as closely related structures of 2,6-bis(diphenylphosphinoyl)pyridine and 9-(diphenylphosphinoyl)-1,10-phenanthroline-2-one, are reported. Complexes of nitrates of several lanthanides and trifluoroacetate of Eu(iii) with two phosphinoyl-bearing 2,2'-bipyridyl and phenanthroline ligands were isolated and characterised. The first structures of lanthanide complexes with phosphinoyl-bearing 2,2'-bipyridyl and phenanthroline ligands are reported. The nature of the counter-ion is crucial for the coordination environment of the metal ion. The photophysical properties of the complexes differring in both the nature of the ligand and counter-ion were investigated. The photophysical properties of the complexes are strongly ligand- and counter-ion-dependent. Absorbance and luminescence excitation spectra of complexes showed main peaks in the UV range which correspond to the absorption of light by the ligand and these are ligand-dependent. Luminescence spectra of complexes show typical europium emission in the red region with a high quantum yield, which corresponds to the transitions 5D0 → 7FJ (J = 0-6). The value of deviation of the components of 5D0 → 7F2 and 5D0 → 7F1 transitions from the inversion centre shows a larger dependence on the counter-ion than on the nature of the ligand. The value of the luminescence quantum yield is larger for europium complexes with 2,2'-bipyridyl-based ligands and NO3 counter-ions than for complexes with phenanthroline-based ligands and NO3 counter-ions. A low dependence of the luminescence lifetime of Eu complexes on the nature of the ligand has been demonstrated: values in the solid state were in the range 1.1-2.0 ms.