Β-diketonate Ligands Research Articles

Structures and pure near-infrared photophysics of erbium and ytterbium(iii) complexes incorporating fluorinated β-diketone and neutral unidentate ligands

This paper reports on the synthesis, structures and pure near-infrared photophysical properties of low symmetry Er3+ and Yb3+ β-diketonate ternary complexes.

Coordination microenvironment perturbed single-ion magnet behavior in a β-diketone Dy(iii) complex

Employing mixed β-diketonate and bpy ligands leads to a mononuclear Dy(iii) SIM, of which the magneto-structural correlation is elucidated by the magnetic and theoretical studies, as well as a comparative study of reported analogues.

Intense red luminescent materials of ternary Eu3+ complexes of oxide ligands for electroluminescent display devices

Solid ternary compounds of Eu(III) with fluorinated β-diketone (4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) (Hfth) and heteroaromatic monodentate ancillary ligands (aqua/triphenylphosphineoxide/pyridine-N-oxide/2-pyridionl-N-Oxide) were prepared for red color emissive materials. The luminescence characteristics of prepared compounds were illustrated using absorption and emission spectral measurements which specified that the β-diketone ligand could effectively sensitized the central europium ion meant for the improved emission of the light. Due to interaction metal complexes displays distinguished effectual on photoluminescence efficacy (η) as well as Judd Ofelt luminous factor (Ω2). An extensive relative approach of enhancement in luminescent behavior of the synthesized metal complexes had been carried out by replacing aqua ligand in the inner coordination sphere of conventionally prepared parent aqua complex with others ancillary oxide ligands to make metal complex co-coordinatively saturated as well as suitable for fabricating electroluminescent display devices.

Vibrational Quenching in Near-Infrared Emitting Lanthanide Complexes: A Quantitative Experimental Study and Novel Insights.

Two series of novel NIR-emissive complexes of Nd3+ , Sm3+ , Er3+ and Yb3+ with two different β-diketonate ligands (L1 =4,4,4-trifluoro-1-phenyl-1,3-butadione and L2 =4,4,4-trifluoro-1-(4-chlorophenyl)-1,3-butadione) are reported. The neutral triphenylphosphine oxide (tppo) ligand was used to replace coordinated water molecules in the first coordination sphere of the as-obtained [Ln(L1(2) )3 (H2 O)2 ] complexes to afford water-free [Ln(L1(2) )3 (tppo)2 ] molecular species. Upon replacement of water molecules by tppo units, the NIR emission lifetimes of the Nd3+ , Er3+ and Sm3+ complexes increase by about one order of magnitude up to values of ≈9, 8 and 113 ms while Yb3+ complexes reach intrinsic quantum yields as high as to ΦYb =6.5 %., which are remarkably high for fully hydrogenated complexes. Vibrational quenching by CH and OH oscillators has been quantitatively assessed by implementing the Förster's model of resonance energy transfer on the basis of experimental data. This study demonstrates that highly efficient NIR-emitting lanthanide complexes can be obtained with facile, cheap and accessible syntheses through a rational design.

Controlled Heterometallic Composition in Linear Trinuclear [LnCeLn] Lanthanide Molecular Assemblies.

The combination of two different β-diketone ligands facilitates the size-controlled assembly of pure heterometallic [LnLn'Ln] linear compounds thanks to two different coordination sites present in the molecular scaffold. [HoCeHo], [ErCeEr], and [YbCeYb] analogues are presented here and are characterized both in the solid state and in solution, demonstrating the selectivity of this unique method to produce heterometallic 4f molecular entities.

Synthesis, characterization, DNA/BSA interactions and in vitro cytotoxicity study of palladium(II) complexes of hispolon derivatives

Thirteen novel palladium(II) complexes of the general formula [Pd(bipy)(O,O′-dkt)](PF6), (where bipy is 2,2′-bipyridine and O,O′-dkt is β-diketonate ligand hispolon or its derivative) have been prepared through a metal-ligand coordination method that involves spontaneous formation of the corresponding diketonate scaffold. The obtained palladium(II) complexes have been characterized by NMR spectroscopy, ESI-mass spectrometry as well as elemental analysis. The cytotoxicity analysis indicates that most of the obtained palladium(II) complexes show promising growth inhibition in three human cancer cell lines. Flow cytometry analysis shows complex 3e could promote intracellular reactive oxygen species (ROS) accumulation and lead cancer cell death. And the suppression of ROS accumulation and the rescue of cell viability in HeLa cells by N-acetyl-L-cysteine (NAC) suggest the possible link between the increase in ROS generation and cytotoxicity of complex 3e. Flow cytometry analysis also reveal that complex 3e cause cell cycle arrest in the G2/M phase and collapse of the mitochondrial membrane potential, promote the generation of ROS and lead to tumor cell apoptosis. The interactions of complex 3e with calf thymus DNA (CT-DNA) have been evaluated by UV–Vis spectroscopy, fluorescence quenching experiments and viscosity measurements, which reveal that the complex interact with CT-DNA through minor groove binding and/or electrostatic interactions. Further, the results of fluorescence titration and site marker competitive experiment on bovine serum albumin (BSA) suggest that complex 3e can quench the fluorescence of BSA via a static quenching process and bind to BSA in Sudlow's site II.

Crystal structure, anti-Trypanosoma cruzi and cytotoxic activities of Cu(II) complexes bearing β-diketone and α-diimine ligands

Three novel copper(II) complexes were synthesized: [Cu(tfa)2] (I), [Cu(tfa)(dmb)(NO3)].1.5H2O (II) and [Cu(tfa)(nphen)(NO3)] (III), where tfa = 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione, nphen = 5-nitro-1,10-phenanthroline and dmb = 4,4-dimethoxy-2,2-bipyridine. They were characterized by elemental analysis, conductivity measurements, FT-IR, UV–Vis and single-crystal X-ray diffraction. The X-ray crystal structures of I, II and III reveal that the β-diketone coordinates via the oxygen atoms, while the heterocyclic bases coordinate via their two nitrogen atoms. The cytotoxic activity of I, II and III was investigated in two tumor cell lines (Ehrlich tumor and sarcoma 180) and in a non-tumor cell line (myoblast C2C12). Complex III exhibited good activity (IC50 Ehrlich = 15.75 μM and IC50 sarcoma 180 = 16.90 μM) and selectivity (SI > 4) in both tumor cell lines. Subsequently, it was found that III also present good activity against Trypanosoma cruzi.

Redox Properties of Mononuclear Dicarbonyl and Carbonylphosphine Rhodium (I) Complexes Containing β-diketonate Ligands

The redox properties of mononuclear dicarbonyl and carbonylphosphine rhodium (I) complexes (CO)(L)Rh(RC(O)CHC(O)R’) with chelate β-diketonate ligands (L = CO, PPh3; R, R’ = Me, Ph; CF3, C4H3S) were studied by electrochemical methods at platinum, glassed carbon and dropping mercury electrodes in acetonitrile. Schemes of their redox reactions were established

Excited state energy transfer from terminal β-diketonate ligands to a central boron dipyrrin (Bodipy), mediated by lanthanide (III) metals

A new boron-dipyrromethene (Bodipy) dye with phenanthro-fused groups at the β-pyrrole positions is described. The π-extended pyrrole units result in intense red-shifted absorption and emission in the visible region of the spectrum. The phenathroline groups are incorporated to allow for coordination of Ln(III) β-diketonates giving the first examples of bis-Ln(III)-Bodipy complexes (where Ln = Eu and Tb). Electronic spectroscopy of the disubstituted Ln(III)-Bodipy complexes reveal β-diketonate charge transfer in the ultraviolet region of the spectrum and π π * transitions associated with the Bodipy core. Upon excitation of the terminal antenna β-diketonate ligands, within the ultraviolet region, emission of the Bodipy core is observed with no evidence of Ln(III) emission; suggesting energy transfer from the antenna ligands to the lanthanide ion to the Bodipy core (An → Ln(III) → Bodipy).

Neodymium ternary complexes with 2,4,6-tri(2-pyridyl)-1,3,5-triazine: Synthesis, crystal structure and fluorescence property

Two neodymium β-diketonates metal-organic complexes, Nd(TTA)3TPTZ (1) and Nd(BFA)3TPTZ (2), have been synthesized by using two β-diketone ligands 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (HTTA) and 4,4,4-trifluoro-1-phenyl-1,3-butanedione (HFBA), and a macrocyclic conjugate ligand, 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ). The crystal structures of these two complexes were determined by single crystal X-ray diffraction. The X-ray diffraction analysis showed that each neodymium ion in the two complexes formed a Nine-Coordinated structure with six oxygen atoms of HTTA (or HBFA) ligands and three nitrogen atoms of TPTZ ligand by the characteristic of triclinic with P1(—) space group both. In the crystal structure of the two complexes, a very obvious aromatic donor-acceptor interaction can be observed between adjacent TPTZ ligand molecules, which play an important role in the formation of three-dimensional structures. The complexes were also characterized by infrared spectroscopy, elemental analysis, thermogravimetric and fluorescence spectra. Fluorescence analysis showed that the two complexes exhibited characteristic neodymium-centered emission due to the significant antenna effect of these ligands.

Different single-molecule magnets behaviors of carboxyl bridged dinuclear Dy(III) complexes induced by charged and neutral ligand

Three dinuclear dysprosium complexes, namely, Dy2(DBM)4L2(CH3CH2OH)2·2CH2Cl2(1), Dy2(DBM)4L2(CH3OH)2·2CH2Cl2(2), Dy2(BAC)4L2(CH3CH2OH)2 (3) and yttrium compound Y2(BAC)4L2(CH3CH2OH)2 (3Y) (L = 2,6-dimethoxybenzoic acid, DBM = dibenzoyl methane, BAC = Benzoylacetone), were structurally and magnetically characterized. The single-crystal structures showed that L serves as an effective bridge to link two Dy(III) centers with μ2-η1:η2-O2 coordination mode. Each Dy(III) ion was chelated by two bidentate β-diketonate co-ligands and a methanol or ethanol molecule, leading to an eight-coordinated geometry. The magnetic measurements revealed that all the complexes behaved as field-induced single-molecule magnets, and the ferromagnetic intramolecular interactions between Dy(III) ions are apparent. Strikingly, the alteration of neutral ligands between 1 and 2 did not result in a significant change of their relaxation energy barriers (Ueff/kB = 25.6 K and 26.1 K respectively), while the dramatically enhancement of energy barrier by nearly triple (91.6 K) increase was observed in 3 when modulating the terminal of β-diketonate anion and the open butterfly-shaped hysteresis loop was also observed at 1.8 K in 10% diluted samples of 3. The electrostatic model for the determination of the magnetic anisotropy in Dy complexes implemented by the Magellan program revealed that the dynamic magnetic relaxation is dominated by the charged β-diketonate ligand much more than the neutral ligand in this case.

MIXED-LIGAND ACETYLACETONATE COMPLEXES OF LANTANUM (III) AND GADOLINIUM (III) WITH CARBOXYLIC ACIDS AND ACETONITRILE OR DIMETHYLFORMAMIDE

This paper presents the study of mixed-ligand complexes of Ln(III), which are used as volatile precursors in CVD processes for the preparation of lanthanide-containing films and coatings. New mixed-ligand acetylacetonate complexes of lanthanides (III) with acetic (propionic) acid and acetonitrile or dimethylformamide were synthesized and investigated by physic-chemical methods of analysis (elemental analysis, differential thermal analysis, IR spectroscopy, powder X-ray diffraction). Using mixed-ligand complexation, the properties of the initial lanthanide β-diketonates (in particular, chemical and thermal stability) can be changed significantly.
 To assess the stability of the synthesized mixed-ligand complexes, their quantum-chemical modeling was performed using the semi-empirical method Sparkle/PM7. Standard changes of the Gibbs energy ∆G0298 were calculated for the solution reaction of (1) synthesis of mixed-ligand complexes and (2) substitution of one of the β-diketonate ligands in the Ln(III) tris-acetylacetonates dihydrates by an acetate ion or propionate ion. The ∆G0298 values for the syntesis reaction mainly increases with increasing donor basicity and decreasing ionic radii Ln(III) in the La>Gd>Lu series. For all mixed ligand complexes of Ln(III), the heats of formation are negative, which indicates their thermodynamic stability in solution.
 It was established that the obtained complexes have the same composition of the general formula [Ln(AA)2·L·2D], where Ln (III) = La, Gd; НАА- acetylacetonе; L - anion of acetic (HAc) or propionic (HРrop) acids, D- acetonitrile (AN), dimethylformamide (DMFA).
 The results of the thermal analysis confirm the computational data: in the case of the lanthanum mixed-ligand complexes, the carboxylic acid is coordinated to the central ion through bridging carboxylate-ions, which contributes to the formation of oligomers. The lanthanum mixed-ligand complexes are not volatile due to their oligomeric structure. On the other hand, similar gadolinium complexes are monomeric and sublimate at 180 - 350 °C.

Smart All-in-One Thermometer-Heater Nanoprobe Based on Postsynthetical Functionalization of a Eu(III)-Metal-Organic Framework.

Real-time temperature feedback in tissue based on photothermal therapy is an urgent problem to be solved in cancer treatment. Herein, a smart all-in-one nanoprobe THA@Eu-NMOF@Fe/TA was designed and assembled by postsynthetical functionalization of an Eu(III)-based nanoscale metal-organic framework (Eu-NMOF) with a two-photon-absorbing β-diketonate ligand 4,4,4-trifluoro-1-(9-hexylcarbazol-3-yl)-1,3-butanedione (HTHA) and Fe(III)/tannic acid assembly (Fe/TA). Such a functionalized material can simultaneously achieve the temperature-sensing and optical heating under a single beam of near-infrared (NIR) light. Under 808 nm laser excitation, real-time feedback of temperature by monitoring thermoresponsive fluorescence emission ratio ( I616/ I590) and fluorescence lifetime of Eu(III) ions were realized. Meantime, Fe/TA served as the photothermal agent and antibacterial agent to implement photothermal therapy (PTT) and antibacteria simultaneously. The functions of the nanoprobe were proved with ex vivo experiments, and the antibacterial activity against Gram-positive and Gram-negative bacteria of the probe was also elaborately evaluated. Our work paves a new avenue for engineering a new cancer treatment probe which can achieve real-time temperature sensing feedback during PTT and antibacterial process.

Comparative solution and structural studies of half-sandwich rhodium and ruthenium complexes bearing curcumin and acetylacetone

Half-sandwich organometallic complexes of curcumin are extensively investigated as anticancer compounds. Speciation studies were performed to explore the solution stability of curcumin complexes formed with [Rh(η5-C5Me5)(H2O)3]2+. Acetylacetone (Hacac), as the simplest β-diketone ligand bearing (O,O) donor set, was involved for comparison and its Ru(η6‑p‑cymene), Ru(η6‑toluene) complexes were also studied. 1H NMR, UV–visible and pH-potentiometric titrations revealed a clear trend of stability constants of the acac complexes: Ru(η6‑p‑cymene) > Ru(η6‑toluene) > Rh(η5-C5Me5). Despite this order, the highest extent of complex formation is seen for the Rh(η5-C5Me5) complexes at pH 7.4. Formation constant of [Rh(η5-C5Me5)(H2curcumin)(H2O)]+ reveals similar solution stability to that of the acac complex. Additionally, structures of two complexes were determined by X-ray crystallography. The in vitro cytotoxicity of curcumin was not improved by the complexation with these organometallic cations.

Synthesis, structure and thermal investigation of a new volatile iridium (I) complex with cyclooctadiene and methoxy-substituted β-diketonate

The presence of donor groups in volatile metal compounds is interesting both in the thermochemical aspect and as the possibility to form hetero-metallic precursors by a reaction with an acceptor-capable component. Following this trend, the present work deals with synthesis and detailed structural and thermochemical investigation of a first iridium volatile complex with donor-atom-functionalized β-diketonate ligand, namely [Ir(cod)(zis)] (cod = cyclooctadiene-1,5, zis = 2-methoxy-2,6,6-trimethylheptanedionato-3,5). The compound has been characterized by elemental analysis, IR- and NMR-spectroscopy. According to single-crystal X-ray diffraction, the crystal structure of the complex is formed by layered-packed isolated molecules. Within the molecules, the coordination site IrO2C′2 (C′ is the center of C=C bond of the cod-ligand) is implemented to form distorted planar square metal coordination environment with Ir–O and Ir–C′ distances being (2.034–2.046) and (1.965–1.978) A, respectively. TG–DTA study shows that the compound is characterized by extremely low melting point (378 K) and a high thermal stability during evaporation. Then, the temperature dependencies of saturated vapor pressures over both the solid and liquid compounds have been measured by the flow (transpiration) method at (353–376) K and (381–403) K, respectively, giving the molar enthalpy and entropy of sublimation and evaporation processes. In addition, the comparison of the structural and thermal data with the ones for the related [Ir(cod)(L)] complexes containing symmetric alkyl terminal substituents in β-diketonate ligand L has been performed and, thereby, the donor group influence on the characteristics of this type of volatile compounds has been revealed.

Ligand ratio/solvent-influenced syntheses, crystal structures, and magnetic properties of polydentate Schiff base ligand-Dy(iii) compounds with β-diketonate ligands as co-ligands.

Tuning the synthesis conditions and further regulating the magnetic dynamics of single-molecule magnets (SMMs) are crucial challenges for chemists. Some feasible approaches have been developed to understand magneto-structural correlations and regulate relaxation behaviors via rational design. Based on the solvent-induced effect or ligand ratio regulation, three new dysprosium(iii) coordination compounds, [Dy(L)(Dppd)]·solvent (1), [Dy(L)(Dppd)] (2) and [Dy(L)(Dppd)2]·solvent (3) (H2L = N,N'-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine, Dppd = dibenzoylmethane) have been successfully prepared. Compounds 1 and 2 are mononuclear structures. 3 is a dinuclear core in which the metal centers are bridged by two phenol-O atoms of one L2- ligand. Dy(iii) cations in compounds 1-3 present acta-coordination geometries. More interestingly, compounds 1 and 2 can be mutually transformed through the reversible single-crystal-to-single-crystal (SCSC) transformation under different solvent environments. The crystals of 1 and 2 underwent a dissolution-precipitation process and changed into 3, respectively. The distinct structures and magnetic properties were determined through combined structural, experimental and theoretical investigations.

Designing a mononuclear DyIII single-molecule magnet (SMM) by using a N,O,N,O-based multichelating Schiff base ligand and a β-diketonate ligand

Two mononuclear LnIII compounds, in which each LnIII is eight-coordinated, namely [Ln(L)(tmpd)] (Ln = Dy (1) or Er (2)), have been prepared using a multichelating Schiff base ligand (H2L) and a bidentate chelating β-diketonate ligand (tmpd).

Symmetry correlations between crystallographic and photoluminescence study of ternary β-diketone europium(iii) based complexes using 1,10-phenanthroline as the ancillary ligand.

This work entails deep red emitting EuIII based complexes with a variety of ternary β-diketonate ligands and 1,10-phenanthroline as the ancillary ligand in the system. The solid state structure and spectroscopic analysis has been outlaid in terms of photoluminescence and crystallography. A luminescence quantum efficiency of 50% was obtained for the [tris-(4,4,4-trifluoro-1-chlorophenyl-butanedione)mono-(1,10-phenanthroline)europium(iii)] complexes. Moreover, complexes [tris-(2,2,6,6-tetramethyl-heptanedione)mono-(1,10-phenanthroline) europium(iii)] and {[hexa-(benzyl carboxylic acid) bis-(1,10-phenanthroline)di-europium(iii)]-μ-[κ2-O,O'-(benzyl carboxylic acid)]2} were found to also have quantum yields of 9% and 28% with respective sensitization efficiencies of 85%, 15% and 58%. These results were articulated with crystallographic details pertaining to the nature of coordination and the effect of steric and electronic properties thereof which somewhat impacts the Eu-N bond distances. A symmetry correlation was drawn between the crystallographic data and the photoluminescence data.

Synthesis and photophysical properties of europium pentafluorinated β-diketonate complexes

Two pentafluorinated β-diketone ligands, 4,4,5,5,5-pentafluoro-1-(4-methoxyphenyl)pentane-1,3-dione (PFMP) and 4,4,5,5,5-pentafluoro-1-(4-dimethyl amino-phenyl)pentane-1,3-dione (PFAP), had been employed to synthesize six novel europium (III) complexes with ancillary ligands 2,2-dipyridine, 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline. The synthesized europium (III) complexes were characterized by FTIR, 1H NMR, UV–Vis, luminescence spectroscopy, elemental analysis and thermogravimetric analysis. The photoluminescence spectra of these complexes showed the typical europium (III) red emissions in solid state and chloroform solution, assigned to 5D0 → 7Fj (j = 0–4) transitions. The higher values of intensity parameter Ω2 indicated that the europium ion was in a highly polarizable ligand field in these complexes. Europium (III) complexes with the β-diketone PFMP exhibited much better photoluminescence properties than complexes with the β-diketone PFAP. Especially, the europium (III) complex of the β-diketone PFMP with the auxiliary ligand 2,2-dipyridine displayed the longest lifetime value, the highest quantum yield and good CIE color coordinates matching the pure red color (x = 0.67, y = 0.33) in these complexes. In addition, the proposed energy transfer mechanisms and the thermal stability of these complexes were also investigated and analyzed.

Iron(III) β-diketonates: CVD precursors for iron oxide film formation

Complexes [Fe(β-diketonate)3] (β-diketonate = 2-acetylcyclopentanoate (3a), = 2-acetylcyclohexanoate (3b), = 4,4-dimethyl-1-phenyl pentanedionate (3c)) were synthesized by the reaction of FeCl3 with the respective β-diketones in presence of NaOH. The molecular structures of 3a and 3c in the solid state are discussed, confirming an octahedral coordination sphere at Fe(III) setup by the three bidentate-bonded β-diketonato ligands. Variation of the β-diketonato ligands allowed to influence the thermal behavior and vapor pressure of the complexes. TG-MS ( = Thermo Gravimetry-Mass Spectrometry) studies, exemplarily carried out on 3a, confirmed the release of the β-diketonate ligands. Complexes 3a–c were applied as MOCVD (=Metal-Organic Chemical Vapor Deposition) precursors for the deposition of Fe2O3 thin films on silicon substrates. It was found that with 3a,b, conformal and dense carbon-free γ- and α-Fe2O3 layers were produced at 450 °C, which was verified by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photon spectroscopy.