Lanthanide-induced Shifts Research Articles

Structure Determination of 1,3-Dioxolane-Containing Lipids from the Marine Sponge Leucetta sp. Using Chiral 1H NMR Analysis of Model Systems.

Chemical investigation of n-hexane extract from the marine sponge Leucetta sp. led to the isolation of five new lipids, 1-5, each characterized by a substituted dioxolane core. The structures of 1-5 were established based on the interpretation of NMR and HRESIMS data. To assign the absolute configuration at C-1', model systems consisting of diastereomers at C-2, C-4, and C-1' of the dioxolane core were prepared from a chiral glycerol dimethylacetal. 1H NMR inspection of model compounds revealed that a pair of C-1' epimers, 11a/c and 11b/d, was indistinguishable, restricting structural assignment by direct comparison of NMR data. In addition, the lack of chromophores in the dioxolane core resulted in unreliable ECD results, with Cotton effects appearing below 190 nm. As an alternative, a chiral NMR method using Eu(hfc)3 revealed notable lanthanide-induced shifts, allowing the spectroscopic discrimination of 11a/c and ent-11a/c. Therefore, the absolute configuration of all five new lipids was determined to be 2S, 4S, 1'S by direct comparison with the Eu(hfc)3-induced 1H NMR data.

Site-Selective Solvation-Induced Conformational Switching of Heteroleptic Heteronuclear Tb(III) and Y(III) Trisphthalocyaninates for the Control of Their Magnetic Anisotropy.

In the present work, we report the synthesis of isomeric heteronuclear terbium(III) and yttrium(III) triple-decker phthalocyaninates [(BuO)8Pc]M[(BuO)8Pc]M*[(15C5)4Pc] (M = Tb, M* = Y or M = Y, M* = Tb, [(BuO)8Pc]2--octa-n-butoxyphthalocyaninato-ligand, [(15C5)4Pc]2--tetra-15-crown-5-phthalocyaninato-ligand). We show that these complexes undergo solvation-induced switching: the conformers in which both metal centers are in square-antiprismatic environments are stabilized in toluene, whereas in dichloromethane, the metal centers M and M* are in distorted prismatic and antiprismatic environments, respectively. This conclusion follows from the detailed analysis of lanthanide-induced shifts in 1H NMR spectra, which makes it possible to extract the axial component of the magnetic susceptibility tensor χaxTb and to show that this term is particularly sensitive to conformational switching when terbium(III) ion is placed in the switchable "M" site. This result provides a new tool for controlling the magnetic properties of lanthanide complexes with phthalocyanine ligands.

Structure Determination of Binuclear Triple-Decker Phthalocyaninato Complexes by NMR via Paramagnetic Shifts Analysis Using Symmetry Peculiarities.

The detailed knowledge about the structure of multinuclear paramagnetic lanthanide complexes for the targeted design of these compounds with special magnetic, sensory, optical and electronic properties is a very important task. At the same time, establishing the structure of such multinuclear paramagnetic lanthanide complexes in solution, using NMR is a difficult task, since several paramagnetic centers act simultaneously on the resulting chemical shift of a particular nucleus. In this paper, we have demonstrated the possibility of molecular structure determination in solution on the example of binuclear triple-decker lanthanide(III) complexes with tetra-15-crown-5-phthalocyanine Ln2[(15C5)4Pc]3 {where Ln = Tb (1) and Dy (2)} by quantitative analysis of the pseudo-contact lanthanide-induced shifts (LIS). The symmetry of complexes was used for the simplification of the calculation of pseudo-contact shifts on the base of the expression for the magnetic susceptibility tensor in the arbitrary oriented magnetic axis system. Good agreement between the calculated and experimental shifts in the 1H NMR spectra indicates the similarity of the structure for the complexes 1 and 2 in solution of CDCl3 and the structure in the crystalline phase, found from the data of the X-ray structural study of the similar complex Lu2[(15C5)4Pc]3. The described approach can be useful for LIS analysis of other polynuclear symmetric lanthanide complexes.

NMR estimation of the activation energy of conformational dynamics in the [Dy(DOTA)]− complex: Energetic manifestation of the gadolinium break

The conformational dynamics of the paramagnetic complex [Dy(H2O)n(DOTA)]− has been studied by dynamic 1H NMR within the framework of the signal bandshape analysis technique taking into account the temperature variation of the lanthanide-induced shifts (LIS). The corresponding values of the free energy of activation ΔG≠298 were 68 kJ/mol for the SAP → TSAP transformation process, and 60 kJ/mol for the reverse transition (TSAP → SAP). In the series of [Ln(H2O)n(DOTA)]− complexes from praseodymium to lutetium, there is first a monotonic increase in the free energy of activation ΔG≠298 of the conformational transition up to Dy, then there is a gradual decrease in the activation barrier (as a manifestation of the gadolinium break effect).

1H NMR spectral analysis of structural features in a series of paramagnetic homoleptic binuclear triple-decker phthalocyaninato lanthanide complexes

The search for efficient methods of comparative structural investigations of coordination compounds in solid state and solutions is a very relevant task. In this study, structural assignments in a series of Ln2[(15C5)4Pc]3 complexes (where [(15C5)4Pc]2- is 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato-dianion, Ln = Nd3+, Tb3+, Dy3+, Ho3+, Er3+ and Tm3+) was performed using NMR relaxation and paramagnetic lanthanide-induced shifts (LIS) data. Analysis of the paramagnetic chemical shifts and relaxation rates evidenced of isostructurality of the complete series of the investigated triple-decker complexes in the solutions. The performed systematic DFT calculations for a series of model complexes with methoxy-substituted ligands Ln2[(MeO)8Pc]3 demonstrate that the calculated geometrical factors are in agreement with characteristics extracted from experimental NMR data.

Lanthanide complexes with polyaminopolycarboxylates as prospective NMR/MRI diagnostic probes: peculiarities of molecular structure, dynamics and paramagnetic properties.

The paramagnetic lanthanide complexes with polyaminopolycarboxylate (PAPC) ligands attract considerable attention from the standpoint of potential applications thereof as relaxation agents used in medical magnetic resonance imaging (MRI) and in luminescent materials, as well as owing to promising use thereof as paramagnetic labels for studying the properties of biopolymers since they exhibit thermodynamic stability, good solubility in aqueous media and moderate toxicity. For the last decades, the NMR methods have been used to determine the physical and chemical properties of paramagnetic Ln compounds. The studies concerning paramagnetic NMR lanthanide-induced shifts (LISs) in dissolved Ln complexes, as well as the analysis of band shape as a function of temperature make it possible to obtain valuable information on the structure, intra- and intermolecular dynamics and paramagnetic properties thereof. This review is devoted solely to the following features: firstly, the processes of intramolecular dynamics of lanthanide complexes with polyamino-polycarboxylate ligands such as DOTA, EDTA and DTPA and their derivatives studied by NMR; secondly, the LISs of lanthanide complexes with EDTA, DOTA, DTPA and some of their derivatives depending on temperature and pH. Moreover, in this review, for the first time, the dependence of the activation energy of molecular dynamics in complexes with polydentate ligands on the atomic number of the lanthanide cation is analyzed and a monotonic change in energy is detected, which is due to the effect of lanthanide contraction. It should be noted that this phenomenon is quite general and may also appear in the future in many other series of lanthanide complexes with both other multidentate ligands and with bidentate and monodentate ligands. In the future, it is possible to predict the dependence of the properties of certain lanthanide complexes on the ionic radius of the lanthanide cation based on the approaches presented in the review. In this review, we have also presented the dynamic NMR as the main research method widely used to analyze the processes of molecular dynamics, and the structural studies based on the NMR relaxation spectroscopy and LIS analysis.

Total Synthesis via Biomimetic Late-Stage Heterocyclization: Assignment of the Relative Configuration and Biological Evaluation of the Nitraria Alkaloid (±)-Nitrabirine.

The racemic total synthesis of nitrabirine (5) together with its previously undescribed epimer 2-epi nitrabirine (5') is accomplished via a six-step route based on a biomimetic late-stage heterocyclization. This allowed the assignment of the relative configuration of nitrabirine by the lanthanide-induced shifts (LIS) experiment, which was later on confirmed by X-ray diffraction of obtained single crystals. Furthermore, oxidation studies demonstrated that the direct N-oxidation of nitrabirine does not yield nitrabirine N-oxide as reported earlier. In contrast, the reaction of hydrogen peroxide with nitrabirine (5) yields the salt 24', whereas 2-epi nitrabirine (5') surprisingly leads to a previously uncharacterized product 22 under the same conditions. Finally, a Fischer indole reaction gave access to novel tetracyclic nitrabirine derivatives 26a-d. A comprehensive biological evaluation of nitrabirine (5), 2-epi nitrabirine (5'), and all derivatives synthesized in this study revealed general biofilm dispersal effects against Candida albicans. Moreover, specific compounds showed moderate antibacterial activities as well as potent cytotoxic activities.

Intermolecular dynamics and paramagnetic properties of Tm-Na heterometallic complex with macrocyclic ligand by 23Na dynamic NMR

The temperature dependence of lanthanide-induced shifts (LIS) and chemical exchange rate constants are studied. The analysis of chemical exchange rate constants was carried out using the method of analysis of the bandshape taking into account the temperature change in the LIS. The value of Gibbs free energy for the activation of intermolecular dynamics is ΔG≠(298 K) = 55 ± 2 kJ/mol. Method of analysis of the bandshape taking into account the temperature change in the paramagnetic lanthanide-induced shifts used for estimation the activation energy of intermolecular dynamics ΔG≠(298 K) = 55 ± 2 kJ/mol.

NMR Spectroscopy—A Versatile Tool for Studying the Structure and Magnetic Properties of Paramagnetic Lanthanide Complexes in Solutions (Review)

Coordination compounds of lanthanides attract increasing attention of researchers due to their unique physical and chemical properties, including interesting optical and magnetic behavior. Fine tuning of properties of functional materials based on them is possible by controlling the structure of complexes. This review describes the approach of applying NMR spectroscopy to solve the challenging problem of identification of paramagnetic lanthanide complexes, as well as to establish a correlation between the structure of the coordination sphere of lanthanide ions and the magnetic characteristics of the complexes. It has been shown how the analysis of lanthanide-induced shifts (LIS) and lanthanide-induced relaxation (LIR) in series of isostructural compounds contributes to the identification of spectral–structural correlations, which, in combination with X-ray diffraction and quantum-chemical data, make it possible not only to establish the structure of the compound in solution, but also to perform a primary assessment of the possibility of using lanthanides complexes as single molecule magnets.

Application of Lanthanide Shift Reagent to the 1H-NMR Assignments of Acridone Alkaloids.

This study investigates the application of the paramagnetic shift reagent tris(dipivaloylmethanato)-europium(III) in NMR spectral studies of permethoxyacridone alkaloids (1–3) and pyranoacridone alkaloids (4–6). The induced chemical shifts (∆δ) of all protons were observed for the same molecule, and were compared to deduce the positions resulting from the distance nearby the Eu(dpm)3. Assignment of the H-2, H-4 and H-8 of polysubstituted acridones could be distinguished based on the least-squares method of lanthanide-induced shifts plotted against the mole ratios of Eu(dpm)3 to the substrate. The developed method is not only potentially useful for determining the planar structures of polysubstituted compounds, such as acridones, anthraquinones, xanthones, flavonoids, and phenanthrenes, but also applicable for their stereochemistry.

Planar and sandwich-type Pr(III) and Nd(III) chlorinated phthalocyaninates: Synthesis, thermal stability and optical properties

A direct synthetic approach to four single-decker and one double-decker novel Pr(III) and Nd(III) complexes with 2,3,9,10,16,17,23,24-octachlorophthalocyaninate and 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecachlorophthalocyaninate has been developed. Synthesis of hexadeca-Cl-substituted Nd(III) bisphthalocyaninate has been carried out utilizing two preformed synthetic blocks: Nd(III) octachlorophthalocyaninate acetate and octachlorophthalocyanine ligand. Due to the electron withdrawing effect of 16 chlorine groups, this Nd(III) bisphthalocyaninate was obtained as a redox stable anionic form. Upfield lanthanide-induced shifts of the aromatic proton signals (up to 2.04 ppm for Pr(III) octachlorophthalocyaninate acetate) were observed in the 1H NMR spectra of the obtained phthalocyaninates. Thermal stability of the lanthanide (III) complexes was examined using thermogravimetric analysis combined with mass-spectrometry. The double-decker compound was shown to possess an increased thermal stability in comparison with the single-deckers up to ~400 °C. Linear and nonlinear optical properties of the Cl-substituted Nd(III) and Pr(III) phthalocyaninates have been investigated using z-scan technique. The best nonlinear optical response with the highest excited state absorption cross-section (σ1 = 1.1 × 10−15 cm−2) was found for the hexadeca-Cl-substituted Nd(III) monophthalocyaninate.

1H NMR of paramagnetic Lanthanide(III) complexes of trifluoroacetylacetone and 2,2′-Bipyridyl and 4f-4f absorption studies

A series of anhydrous eight-coordinate air and moisture stable lanthanide (III) complexes of 1,1,1-trifluoro-2,4-pentanedione (tfaa) and 2,2′-bipyridyl (bpy) of the type [Ln(tfaa)3(bpy)] [Ln = La (1), Nd (2), Ho (3), Er (4), Yb (5) and Lu (6)] have been synthesized in high yield by a one-step method and characterized by elemental analyses, ESI-MS+, TGA, DTA IR and 1H NMR spectroscopy. The NMR spectra of diamagnetic and paramagnetic complexes reveal that the bpy unit remains attached to the metal in solution. The β-diketonate (methine and methyl) and bpy protons resonances are shifted in opposite directions in a given paramagnetic complex and the lanthanide-induced shifts are dipolar in nature. The 4f - 4f absorption spectra of the complexes of Nd(III), Er(III) and Ho(III) are analyzed. The hypersensitive transitions of Nd(III), Er(III) and Ho(III) complexes are sensitive to the environment (ligand/solvent), which is reflected by different oscillator strengths and distinctively different band shapes of the hypersensitive transitions. The coordination geometries of [Ln(tfaa)3H2O] and [Ln(tfaa)3(bpy)] (Ln = La and Nd) are calculated using the Sparkle/PM3 model.

Lanthanide (III) complexes of 3-(ethylthio)phenyl-substituted phthalocyanines: Synthesis and physicochemical properties

Novel phthalocyaninates of terbium, erbium and lutetium, bearing 3-(ethylthio)phenyl peripheral groups, were synthesised with high yields. The complexes obtained were characterised by 1H nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy and high-resolution mass spectrometry. Thermal stability of the lanthanide complexes was examined using thermogravimetric analysis combined with fourier-transform infrared spectroscopy. Strong upfield (up to −59.06) and downfield (up to 22.32) lanthanide-induced shifts of signals of aromatic protons were observed in nuclear magnetic resonance spectra of terbium and erbium complexes respectively. It was shown, that comparing to phenyl-substituted analogues the introduction of ethylthio-moieties in the meta-positions of phenyl substituents does not affect the Q band maxima. Hybrid gold nanoparticles coated with molecules of the lutetium complex were obtained and their optical properties were studied. The formation of phthalocyanine shell and its composition were proven using atomic force and transmission electron microscopy. Absorption cross-sections of ground and the first excited states were calculated using the data of open-aperture z-scan measurements for lutetium complex and hybrid gold nanoparticles on its basis.

A theoretical and NMR lanthanide-induced shift (LIS) investigation of the conformations of lactams.

Molecular mechanics (MM) with MMFF94 and MMX force fields and ab initio (RHF/6-31G*,RHF/6-311G**, and B3LYP/6-311G**) calculations are used with lanthanide-induced shift (LIS) to investigate the conformations of N-methyl-2-pyrrolidone 1, N-methyl-2-piperidone 2, ε-caprolactam 3, γ-valerolactam (1,5-dimethyl-2-pyrrolidone) 4, 2-azetidinone 5, 4-methyl azetidinone 6, 4-phenyl azetidinone 7, and N-methyl-4-phenyl azetidinone 8. The Yb(fod)3 paramagnetic induced shifts of all the 1 H and 13 C nuclei are measured and the corresponding diamagnetic complexation shifts obtained by the addition of Lu(fod)3 . The complexation model (two-, three-, or four-site) used depends on the relative rates of the processes involved. The amide inversion is the same order as that of the 5- and 6-membered lactam rings and much faster than the lanthanide complexation and the inversion of the 7-membered ring. Both MM and ab initio calculations give an envelope conformation for 1 with C-4 out of the ring plane in agreement with the LIS analysis. For the piperidone ring of 2, the half-chair is calculated as the most stable form. The LIS analysis confirms this but cannot exclude a small amount (<2%) of the boat conformation. For 3, the LIS analysis gives a minimum for 90:10% chair to boat conformation, and 4 exists in two envelope conformations with the C5 -Me ps-eq and ps-ax in an eq/ax ratio of 94:6%. In 2-azetidinone 5, the ab initio calculations gave both ring and nitrogen planar, but the MMFF94 calculations give a butterfly ring and pyramidal nitrogen. The LIS analysis for 5 gave good agreement (Rcryst 0.46%) for the MMFF94 geometry with endo NH but the planar ab initio geometries worse agreement (Rcryst=1.1%). For 4-methyl-2-azetidinone 6, the MMFF94 geometry gave good agreement (Rcryst 0.96%) with two butterfly conformations with axial and equatorial methyl groups in 1:1 ratio. All the planar geometries gave worse agreement (Rcryst >1.5%). In 4-phenyl azetidinone 7, the MMFF94 geometry with 60% of the axial conformer gave Rcryst 1.2% but the other geometries Rcryst >1.5%. In contrast the N-methyl-4-phenyl-2-azetidinone 8 gave good agreement for all the geometries. The butterfly conformation gave Rcryst 1.1% for 80% of the axial conformer and the planar geometries Rcryst 0.98%. The LIS results confirm the ab initio and MM optimised geometries, but the conformer energies at times differ from the calculated values. They also differ considerably from the corresponding values for the lactones studied previously, and possible reasons for this are discussed.

Elucidation of 1H NMR Paramagnetic Features of Heterotrimetallic Lanthanide(III)/Manganese(III) 12-MC-4 Complexes.

The paramagnetic one-dimensional 1H NMR spectra of twelve LnIIINaI(OAc)4[12-MCMnIII(N)shi-4] complexes, where LnIII is PrIII-YbIII (except PmIII) and YIII, are reported. Their solid-state isostructural nature is confirmed in methanol-d4 solution, as a similar pattern in the 1H NMR spectra is observed along the series. Notably, a relatively well-resolved spectrum is reported for the GdIII complex. The chemical shift data are analyzed using the "all lanthanides" method, and the Fermi contact and pseudo-contact contributions are calculated for the lanthanide-induced shift (LIS). For the TbIII-YbIII complexes, the pseudo-contact contributions are typically 1 order of magnitude higher than the Fermi contact contributions; however, for the GdIII complex, the Fermi contact is the main contribution to the paramagnetic chemical shift. For the methyl protons of the axial acetate (-OAc) ligands, the LIS is opposite in sign, with respect to that of the aromatic salicylhydroximate (shi3-) protons, because of structural rearrangements that occur upon dissociation of the NaI cation in solution. The calculated crystal field parameters (BLn) for the TbIII (360 cm-1), DyIII (250 cm-1), HoIII (380 cm-1), ErIII (410 cm-1), TmIII (620 cm-1), and YbIII (380 cm-1) complexes are not constant, likely as a consequence of the inaccuracy of the Bleaney's constants and, to a smaller extent, the small structural changes that occur in solution. Overall, the metallacrown scaffold retains structural integrity and similarity in solution for the entire series; however, small structural features, which do not affect the overall similarity, do likely occur.

Lanthanides as NMR/MRI temperature sensors and probes of moderately fast molecular dynamics in aqueous medium: A dependence of activation energy of racemization in complexes of diethylenetriaminepentaacetat on lanthanide ion

In solution, [Ln(H2O)n(dtpa)]2− chelates undergo a dynamic exchange between two enantiomers. The free energy of activation of intramolecular dynamics (for complexes of Pr to Ho) slightly increases with decreasing radius of the lanthanide cation. According to analysis of the paramagnetic lanthanide induced shifts (LIS) in NMR spectra, the structure of [Ho(H2O)n(dtpa)]2− in solution is similar to the related model found in the crystal state. It was found that complexes [Ln(H2O)n(dtpa)]2− may be used (due to the substantial temperature dependence of LIS) as NMR thermometric sensors for controlling the local temperature in aqueous medium. The investigated coordination compounds are suggested to apply as thermo-sensing contrast reagent for MRI diagnostics of cancer and inflammation.

ВПЛИВ Eu(fod)3 НА СПЕКТРИ 1Н ЯМР 3-АРИЛІЗОКУМАРИНІВ ТА 3-АРИЛ-3,4 ДИГІДРОІЗОКУМАРИНІВ З АЛКОКСИЛЬНИМИ, ЕСТЕРНИМИ ТА АМІДНИМИ ГРУПАМИ

The effect of the lanthanide shift reagent (LSR) – tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octa-dionate) of Europium – Eu(fod)3 – on 1H NMR spectra of functionalized 3-arylisocoumarins and 3-aryl-3,4-dihydroisocoumarins was investigated. Based on previous studies of LSR interactions with benzopyrones, it was expected that the main coordination centre for the Eu3+ would be the exocyclic Oxygen atom of the heterocycle, but the possibility of competition from aromatic substituent functional groups was also considered. By measuring lanthanide-induced shifts (LIS) of the proton signals of the molecules at different ratios of substrate and Eu(fod)3, specific LIS values were determined. Based on those, it was concluded that the main direction of LSR coordination with 3-(2-hydroxy-5-methylphenyl)-1Hisochromen-1-one, 3-(2-methoxy-5-methylphenyl)-1H-isochromen-1-one and 3-(2-methoxy-5-methylphenyl)isochroman-1-one is the exocyclic Oxygen atom of the heterocycle, because the maximum LIS were recorded for the H-8 atom of isochromone system of these derivatives. In the case of ethyl ester of [2-(4-(1-oxo-1H-isochromen-3-yl)phenoxy] acetic acid and methyl ester of [2-(4-(1-oxoisochroman-3-yl)phenoxy]acetic acid comparable LIS values were observed both for H-8 and for the methylene group of the hydroxyacetic acid fragment, therefore, in such molecules the coordination of the Eu3+ to the heterocycle or to the aliphatic ester group is almost equally probable. In spectrum of methyl ester of N-{[4-(1-oxo-1H-isochromen-3-yl)phenoxy]acetyl}valine and N-{[4-(1-oxoisochroman-3-yl)-phenoxy]acetyl}valine there are insignificant LIS of H-8; and the maximum LIS were observed for the signals of the protons neighboring the two carbonyl groups of hydroxyacetic acid and valine fragments. Thus, these compounds interact w

Lanthanide Complexes as NMR Paramagnetic Probes for Fast Molecular Dynamics and Relaxation Contrast Reagents for in Situ Control of Temperature

Studies of the paramagnetic lanthanide-induced shifts and relaxation rate enhancements (RRE) in NMR spectra allow to gain quantitative information about the molecular structure as well as the kinetic and thermodynamic stability of paramagnetic complexes in solutions. Several types of molecular dynamics were found by the dynamic NMR in the complexes investigated (e.g. interconversion of complex enantiomeric forms, pseudorotation of a macrocycle molecule, macrocycle molecule inversion and exchange of ligands). Valuable dependence of RRE of lanthanide complexes on the temperature was found. We found experimentally by the paramagnetic NMR that Ln complexes are quite appropriate nano-sized probes for in situ temperature determination in solutions.

Structure elucidation by sparkle/RM1, effect of lanthanide contraction and photophysical properties of lanthanide(III) trifluoroacetylacetonate complexes with 1,10-phenanthroline

Abstract A series of luminescent anhydrous eight-coordinated anhydrous complexes of the general formula [Ln(tfaa)3phen] [Ln = La(1), Pr(2), Nd(3), Eu(4), Tb(5), Dy(6), Ho(7), Er(8), Tm(9), Yb(10) and Lu(11); tfaa = 1,1,1-trifluoro-2,4-pentanedione and phen = 1,10-phenanthroline] have been synthesized and fully characterized by elemental analysis, ESI–MS, thermogarvimetric analysis (TGA), FT-IR and 1H NMR spectroscopy. The complexes retain their identity in solution, phen and β-diketonate (methine and methyl) protons resonances are shifted in opposite directions and lanthanide induced shifts (LISs) is dipolar in nature. The unknown geometry of the complexes was determined from semi-empirical Sparkle/RM1 method. A distorted square antiprism geometry is proposed for [Eu(tfaa)3phen] which is further attested by NMR spectroscopy. The hypersensitive transitions of Nd(III), Ho(III) and Er(III) complexes are sensitive to the environment (solvent), which is reflected by the oscillator strength and band shape of the transitions. The room-temperature PL spectra of Pr(III), Eu(III), Tb(III), Dy(III) and Tm(III) complexes in solution produce their characteristic red, brilliant red, green, yellow and blue emissions, respectively. The replacement of water molecule from the inner-coordination sphere by phen ligand and forming highly protective coordination environment (LnO6N2) by the tfaa− and phen around the Ln(III) ion, leads to increase in the photoluminescence quantum yield (PLQy) and the luminescence lifetime. Theoretical Judd-ofelt and PL parameters of [Eu(tfaa)3phen] complex including PLQy predicted by the Sparkle/RM1 method are in excellent agreement with the experimental values, reflecting the efficacy of this method. The energy transfer processes show that energy transfer occurs via both T → 5D1 (6.98 × 106) and T→ 5D0 (7.39 × 106) levels. Furthermore, Eu and Tb complex display bright red and green luminescence and therefore interesting photonics applications could be foreseen.

Structure and paramagnetic properties of tris-pivaloyltrifluoracetonate thulium(III) complexes with 18-crown-6 by X-ray analysis and NMR

Synthesis and the crystal structure of a novel complex Tm(III) tris-pivaloyltrifluoracetonate, [Tm2(ptf)6] (I) and Tm(III)-tris-pivaloyltrifluoracetonate-(isopropanol)aqua with 18-crown-6 {[Tm(ptf)3(HOCH(CH3)2)H2O]×(18-crown-6)} (II) are reported. A single crystal X-ray diffraction study revealed that complex I has molecular structure which consists of discrete dimeric [Tm2(ptf)6] molecules. Two thulium atoms are located at the 3.7993(2)Å distance. Complex II has molecular structure with hydrogen bonds between oxygen atoms of water molecule and 18-crown-6. Thermogravimetric data evidence the volatility of compound I. It was found by 1H NMR that complexes I, II, [Tm(H2O)(ptf)3] and [Tm(H2O)(ptf)3]×(18-crown-6) may be used (due to the substantial temperature dependence of the paramagnetic lanthanide-induced shifts {LIS}) as NMR thermometric sensors for controlling the local temperature in organic media. According to our information this is the first example of a detailed study of the essential temperature dependence of the LIS on 1/T for Tm complexes in organic media.