Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior

This work reports the energy transfer mechanism process of [Eu(TTA)₂(NO₃)(TPPO)₂] (bis-TTA complex) and [Eu(TTA)₃(TPPO)₂] (tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA=2-thienoyltrifluoroacetone and TPPO=triphenylphosphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogravimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA)₃(TPPO)₂] and [Gd(TTA)₂(NO₃)(TPPO)₂] complexes are associated to T→S₀ transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters Ω_λ (λ=2 and 4), spontaneous emission rates (A_rad), luminescence lifetime (τ), emission quantum efficiency (η) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(III) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA)₂(NO₃)(TPPO)₂] complexes are discussed in terms of ligand-to-metal energy transfer.     

Luminescence of dipicolinic complexes of lanthanide ions

The luminescence decay times τ_lum of the complexes of the ions Tb(III), Eu(III), Sm(III), Dy(III), and Yb(III) with dipicolinic acid (DPA) dissolved in protonated and deuterated water, methanol, and dimethyl sulfoxide are measured. The values of τ_lum for crystals H₃[Ln(DPA)₃]·nH₂O and their aqueous solutions coincide, which points to the identity of the environment in the nearest spheres of an ion in both cases. A comparison of τ_lum of solutions of the complexes in H₂O and D₂O, as well as in CH₃OH, CH₃OD, CD₃OD, DMSO-h ₆, and DMSO-d ₆ shows that the molecular groups in the second and third spheres of an ion, exhibiting high-frequency vibrations, have a noticeable effect on the rate constants of nonradiative transitions k _nr in the ion. From this comparison, some inferences on the structure of the solvate shell of the Ln(DPA) ₃ ^3? complexes in the solvents used are made. The contributions to k _nr of Eu(III), Tb(III), Sm(III), Dy(III), Nd(III), and Yb(III) made by OH and CH groups located at different distances from the ion are estimated. It is demonstrated that the dependence of k _nr on the distance to the OH and CH groups is steeper for the Eu(III) and Tb(III) ions than for the remaining ions.     

Photosensitized luminescence of thermostable polynuclear Eu(III) complexes

Tetranuclear europium(III) complexes, [Eu₄(μ-O)(L₁)₁₀] (L₁=2-hydroxy-4-octyloxybenzophenone,1) and [Eu₄(μ-O)(L₂)₁₀] (L₂=2-hydroxy-4-dodecyloxybenzophenone,2) were synthesized by the reaction of lanthanide nitrates with L₁ or L₂ in the presence of triethylamine in methanol. The photosensitized emission bands of the both Eu(III) complexes in THF-d₈ were observed around 579, 590, 615, 653, and 699 nm by the excitation of the ligands at 380 nm, whereas the emission from the mononuclear complex 3 containing ethanol molecules was almost quenched. The emission efficiencies were determined to be 3.1±0.1% for 1 and 3.9±0.1% for 2, respectively. The differential scanning calorimetry (DSC) measurements demonstrated that the decomposition points of 1 and 2 were 309 °C and 320 °C, respectively, indicating high thermostability of these complexes compared to the mononuclear Eu(III) complex 3 (250 °C). New strategy for designing stable rare earth compounds giving strong emission would be emphasized by introducing polynuclear complexes. Polynuclear complexes should open a wide range of molecular design for photosensitized luminescence and thermal stability.     

Synthesis and spectroscopic and electrochemical properties of binuclear complexes of Au(III) bridged by 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline

A method of synthesis of new diimine complexes of Au(III) with a four-dentate bridging ligand 6,7-dimethyl-2,3-di(2-pyridyl) quinoxaline (Ddpq), [Au₂(μ-Ddpq)Cl₄]Cl₂ and [(AuN^N)₂(μ-Ddpq)](NO₃)₆, where N^N is ethylenediamine, 2,2′-bipyridyl, or 1,10-phenanthroline, is described and the composition, structure, and properties of these complexes are studied. The coordination-induced chemical shifts in the ¹H NMR spectra are determined, as well as the spectral-luminescent and electrochemical parameters of the complexes. The nature of the energetically lowest spin-allowed ¹(π-d*)-and spin-forbidden ³(π-π*) states is established.     

Spectroscopic studies of lanthanide(III) ion complexes with diethyl(phthalimidomethyl) phosphonate

Complexation and photophysical properties of complexes of lanthanide ions, Ln(III), with diethyl(phthalimidomethyl)phosphonate ligand, DPIP, were studied. Interactions between Ln(III) and DPIP were investigated using Nd(III) absorption and Eu(III) and Tb(III) luminescence (emission and excitation) spectra, recorded in acetonitrile solution containing different counter ions (NO₃^-, Cl^- and ClO₄^-). Results of the absorption spectroscopy have shown that counter ions play a significant role in the complexation of Ln(III)/DPIP complexes. Studies of luminescence spectra of Eu(III) and Tb(III) ions proved that the formation of Ln(III)/DPIP complexes of stoichiometry Ln:L=1:3 is preferred in solution. Based on the results of elemental analysis, Nd(III) absorption spectra and IR and NMR data, it was shown that the DPIP ligand binds Ln(III) ions via oxygen from phosphoryl group, forming complexes of a general formula Ln(DPIP)₃(NO₃)₃·H₂O, in which the NO₃^- ions are coordinated with the metal ion as bidentate ligands. Luminescent properties and energy transfer, from the ligand to Ln(III) ions in the complexes formed, were studied based on the emission and excitation spectra of Eu(III) and Tb(III). Their luminescent lifetimes and emission quantum yields were also measured.     

Luminescent europium(III) and terbium(III) nicotinate complexes covalently linked to a 1,10-phenanthroline functionalised sol-gel glass

Sol-gel glasses with covalently linked lanthanide complexes are luminescent materials which can be processed at ambient temperatures, which have a good solubility and uniform distribution of the complexes in the host matrix. In this study, a luminescent terbium(III) complex was covalently coupled to an organic-inorganic hybrid material prepared by the sol-gel process. This was realised by use of nicotinate groups as the ligands for the terbium(III) ion. The [Tb(C₅H₄NCO₂)₃(phen)(H₂O)₂] complex was immobilised on the sol-gel glass matrix and showed a green photoluminescence upon irradiation with ultraviolet light. The nicotinate groups act as an antenna to absorb the incident light and channel the excitation energy to the terbium(III) ion. The sol-gel glass was also prepared for the corresponding europium(III) complex. In this case, excitation of the europium(III) ion was possible via both the nicotinate ligands and the 1,10-phenanthroline ligands. High-resolution luminescence and excitation spectra were recorded and the radiative lifetimes were measured.     

Synthesis,characterization and mesomorphic behaviour of lanthanide (III) 4-alkoxybenzoates

The lanthanide (III) 4-alkoxybenzoates [Ln(C_nH_2n?+?1OC₆H₄CO₂)₃, Ln?=?La (III), Pr (III), Nd (III), Eu (III), Gd (III), Tb (III) and Dy (III) and n?=?6, 8, 10, 12 and 16] have been synthesized and characterized by elemental analyses, magnetic susceptibility measurements, and IR and electronic spectroscopy. Hot-stage polarizing optical microscopy and differential scanning calorimetry have been used to investigate the mesomorphic behaviour. The chain length influences the structure and hence the thermal behaviour of these compounds. All the lanthanide complexes except decyloxy derivatives exhibit smectic A mesophase. The decyloxy-containing complexes are non-mesomorphic. The differential scanning calorimeter traces do not display the exothermic peak for all the compounds except for the hexadecyloxy derivatives, which exhibit enantiotropic smectic A phase. The influence of the lanthanide ions on the phase transition has also been clearly demonstrated.     

Sensitized Near-Infrared Luminescence From NdIII, YbIII and ErIII Complexes by Energy-Transfer From Ruthenium 1,3-Bis([1,10]Phenanthroline-[5,6-d]-Imidazol-2 -yl)Benzene

The luminescent ruthenium 1,3 -bis([1,10]phenanthroline-[5,6 -d]- imidazol-2 -yl)benzene (bpibH₂) complex, a potentially useful bridging ligand with a vacant diimine site, has been used as ‘metallo ligand’ to make heterodinuclear d–f complexes by attachment of a {Ln(dik)₃} fragment (dik?=?1,3-diketonate) at the vacant site. When Ln?=?Nd, Yb, or Er the lanthanide centre has low-energy f–f excited states capable of accepting energy from the ³MLCT excited state of the Ru(II) centre, there is quenching in the ³MLCT luminescence of the Ru(II) centre, that affords sensitized lanthanide(III) based luminescence in the near-IR region. Nd(III) was found to be the most effective at quenching the ³MLCT luminescence of the ruthenium component because of the high density of f–f excited states of the appropriate energy which make it as effective energy-acceptor compared to Er and Yb complexes.     

A facile one-pot solvothermal route to tubular forms of luminescent polymeric networks [(C3N3)2(NH)3]n

A facile one-pot solvothermal route has been developed for the synthesis of tubular luminescent polymeric networks [(C₃N₃)₂(NH)₃]_n, structurally related to the proposed g-C₃N₄. XRD patterns showed a characteristic 002 basal plane diffractions, indicating an interlayer d spacing of 3.23 Å. XPS spectra show that the C1s and N1s have a symmetric peak and an asymmetric peak at 288.10 and 399.00 eV, respectively. The bulk composition C₆N_8.9H_4.5 determined by elemental analysis is comparable to the calculated value C₆N₉H₃ for this proposed polymer. FTIR spectra indicated the presence of s-triazine ring, which was further supported by the luminescent and UV-vis absorption characteristics probably depending on π→π^* electronic transition. The tubular structure has been studied by TEM, SAED, and HREM.     

The optical activity of cobalt(III) chelate diamine complexes

The optical activity of the tris-diamine complexes of cobalt (III) in the visible region is accounted for quantitatively by a coulombic correlation between the components of the electric hexadecapole moment of the ¹ A ₁→¹ T ₁ d-electron transition of the cobalt(III) ion in the [CoN₆] chromophore and a transient electric dipole induced in each ligand group. The correlated electric dipole of the ligand group forms a non-zero scalar product with a component of the magnetic dipole moment of the cobalt(III) ion d-electron transition in the first order employing either an O or a D ₃ effective chromophoric symmetry. The calculated first-order rotational strengths account largely for the observed optical activity due to the chiral puckered conformation of the chelate rings and for the axial single-crystal circular dichroism of a cobalt(III) tris-diamine complex in a uniaxial crystal. The second-order rotational strengths improve the agreement and accommodate the observed circular dichroism of randomly-oriented cobalt(III) tris-diamine complexes. The increase in the dipole strength of the ¹ A ₁→¹ T ₁ transition in a tris-diamine complex, relative to [Co(NH₃)₆]³⁺, is explained by the model in the first order.     

Investigation of the formation of nanostructures of Ln(III) salts with phosphate and carbonate anions using Eu(III) chelates as luminescent markers

The monitoring of variations in the luminescence intensity (I _lum) of nanostructures of Eu(MBTA)₃phen (MBTA is p-methoxybenzoyl trifluoroacetonate) complexes formed in aqueous solutions upon the introduction of anions is proposed as a method of analyzing the composition of Eu(III), Gd(III) and Lu(III) phosphate complexes in solutions with [PO ₄ ^3? ] < [Ln]. It is found that low-lability binuclear complexes, which rearrange within an hour or longer, are formed in these solutions. It is shown that the lability of Ln(III) carbonate complexes exceeds the lability of Ln(III) complexes with PO ₄ ^3? . An analysis of the dependence of I _lum of the solution on the concentration of Eu(III) ions and on the time from the instant of the solution preparation shows that, in aqueous solutions where the concentration of anions is higher than the concentration of Ln(III) ions, nanostructures of Eu(III) phosphate and carbonate salts are formed in the range of Ln(III) concentrations 0.5–5 μM at concentrations of anions on the order of 10 μM and at concentrations of exceeding 100 μM. The rearrangement of these nanostructures to nanostructures of Eu(MBTA)₃phen complexes is studied.     

A Mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D₂O and d ₆-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I _lum and lifetime τ_lum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10^?2–10^?1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10^?6?10^?3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ_lum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).     

Deep-Red Phosphorescent Iridium(III) Complexes Containing 1-(Benzo[b] Thiophen-2-yl) Isoquinoline Ligand: Synthesis,Photophysical and Electrochemical Properties and DFT Calculations

Four new bis-cyclometalated iridium(III) complexes, [Ir(btq) ₂phen] [PF₆] (3a), [Ir(btq) ₂bpy] [PF₆] (3b), [Ir(btq) ₂dtbipy] [PF₆] (3c) and [Ir(btq) ₂pic] (3d) (btq?=?1-(benzo[b] thiophen-2-yl) isoquinoline, phen?=?1,10-phenanthroline, bpy?=?2,2′-bipyridine, dtbipy?=?4,4′-di-tert-butyl-2,2′-bipyridine, pic?=?picolinic acid) have been synthesized and fully characterized. The crystal structure of 3a has been determined by X-ray analysis. The photophysical and electrochemical properties of these new complexes 3a???3d have been studied. The photoluminescence spectra of all Ir(III) complexes exhibit deep-red emission maxima at 682, 682, 683 and 698 nm, respectively. The most representative molecular orbital energy-level diagrams and the lowest energy electronic transitions of 3a???3d have been calculated with density functional theory (DFT) and time-dependent DFT (TD???DFT). The results show that the pic ancillary ligand of complex 3d influences the absorption and emission energies with a further red-shift relative to other three complexes 3a???3c.     

Synthesis and characterization of hexakis(acetonitrile)chromium(III) tetrafluoroborate, [Cr(NCMe)6][BF4]3. A nonaqueous Cr source

Oxidation of [Cr^II(NCMe)₄][BF₄]₂ with thianthrinium tetrafluoroborate forms [Cr^III(NCMe)₆][BF₄]₃ exhibiting two ν_CN absorptions at 2331 and 2301 cm⁻¹, and has been structurally characterized with an average Cr-N distance of 1.999 Å. From the electronic absorption spectra the ligand field splitting, Δ₀, is 20,160 cm⁻¹, which is slightly larger than [Cr^III(OH₂)₆]³⁺ in accord with the divalent chromium analogues. The 298 K ESR has a resonance at g=1.9884, and the magnetic susceptibility has a 300 K moment of 3.85μ_B characteristic of S=3/2 Cr(III). The field dependence of the magnetization can be fit to the Brillouin function also characteristic of S=3/2.     

M?ssbauer Spectroscopy: an elegant tool for the active sites identification and quantification in Pt-Sn-In based naphta reforming catalysts

The reaction of Ln(ClO₄)₃· nH₂O with triphenylphosphine oxide (TPPO) in methanol has led to the formation of [Ln(ClO₄)₂(tppo)₄]ClO₄·MeOH (Ln = Nd, Eu, Gd, Dy, Yb), in which the perchlorate anion acts as a symmetric bidentate. The emission spectra of Eu(III)-TPPO complexes, showing enhancement in the intensity due to the phenyl group, indicate an isotropic electron distribution for the nitrato complex [Eu(NO₃)₃(tppo)₂(EtOH)]. ¹⁵¹Eu and ¹⁵⁵Gd M?ssbauer spectra of the TPPO complexes also lead to the same conclusion.     

ESR investigation of some copper(II)-dioxime-dichloride compounds

The following copper(II)-dioxime-dichloride compounds: [Cu(G)Cl₂]₂, [Cu(P)Cl₂]₂, [Cu(DMG)Cl₂]₂ and [Cu(O)Cl₂]₂ (where G=C₂H₄O₂N₂, P=C₃H₆O₂N₂, DMG=C₄H₈O₂N₂, O=C₈H₁₄O₂N₂) were investigated by ESR method. Spectra of powder samples obtained in the g?2 region suggest the presence of triplet ground state (S=1) realized by a weak ferromagnetic exchange coupling. In liquid and frozen solutions the monomeric species (S=1/2) prevail. Some delicate changes in the coordination polyhedra symmetry in terms of ligand molecules and solvents nature were evidence. A 4p-admixture degree of 2% in the d_xy ground state was estimated for pseudotetrahedral (Td) species in frozen solutions.     

The Infrared Spectra of the First Transition Series Metal(II) Bis(Aquo) Complexes Of 8-Hydroxyquinoline

Abstract

The infrared spectra (700–100 cm^?1) of the complexes [M(ox)₂(H₂O)₂] (ox = 8-hydroxyquinolinate anion, M = Mn, Fe, Co, Ni, Cu, Zn) are discussed. For the purposes of assignment of the metal ligand modes, deuterated 8-hydroxyquinoline-d ₇ was prepared by the Skraup synthesis and the spectra of the deuterated complexes were compared with those of the unlabelled species. Furthermore, [⁶⁴Zn(ox)₂(H₂O)₂] and [⁶⁸Zn(ox)₂(H₂O)₂] were prepared by reaction of ⁶⁴ZnSO₄ and ⁶⁸ZnSO₄ with 8-hydroxyquinoline and the effects of metal isotope labelling on the spectra were examined and compared with earlier isotopic data on the nickel and zinc complexes.     

Positive muons in [Co(NH3)6]Cl3 and [Co(ND3)6]Cl3

We have carried out SR experiments on [Co(NH₃)₆]Cl₃ and [Co(ND₃)₆]Cl₃. At 293 K, all the muons implanted into the complexes were in the diamagnetic state. The observed Gaussian-type muon spin relaxation function proved that the internal magnetic field was caused by nuclear dipole moments of the atoms in the complexes. In addition, another exponential-type muon spin relaxation function was observed in [Co(ND₃)₆]Cl₃ below 50 K.     

Enhanced luminescence of rare-earthTb (III) by Tm (III) in bis(benzoylmethyl) sulfoxide complexes and intra-molecular energy transfer

Rare-earth complexes [(Tb_xTm_y)L₅(ClO₄)₂](ClO₄)·3H₂O(x:y=1.000:0.000, 0.999:0.001, 0.995:0.005, 0.990:0.010, 0.950:0.050, 0.900:0.100, 0.800:0.200, 0.700:0.300; L=C₆H₅COCH₂SOCH₂COC₆H₅) were synthesized and characterized with elemental analysis, infrared spectra (IR) and ¹H NMR. The photophysical properties of these complexes were studied in detail with ultraviolet absorption spectra, fluorescent spectra and lifetimes. The fluorescence spectra and decay curves of complexes indicated that the fluorescence emission intensity was enhanced and the fluorescence lifetime was prolonged by Tm (III), which may be due to the intra-molecular energy transfer between inert rare-earth ions and active rare-earth ions. The complexes showed the best properties when the mole ratio of Tb (III) to Tm (III) is 0.995:0.005. The intensity of fluorescence can be increased to 208%. Additionally, the energy-transfer mechanisms between the ligand and the central Tb (III) ions were discussed.     

Analysis of the ESR Spectrum of a Rhodium (II) Complex

Abstract

Rh(II) complexes are rather scarce¹ and often form dimeric structures, which are diamagnetic. The ESR spectra of definite Rh(II) species have so far been claimed for Rh in ZnWO₃ ², [Rh S₄C₄(CN)₄]^{2 ?}, ^3′4 [Rh(π-C₅H₅)₂]⁵, [(π-C₅H₅)Rh(π-C₂H₄)₂]⁺⁶, and an irradiation produced [RhCπ₂(CN)₄]^{2 ?} complex.⁷ A detailed analysis has been performed on the first², the second⁴ and the last⁷ complexes. The first system shows an almost axial symmetry and the unpaired electron has been assigned to the d_xy orbital² (the x,y,z axes are defined along the octahedral metal-ligand directions). The sulfur ligand complex and the dichlorotetracyano system have their unpaired electron in the d_Z ² orbital. ^4,7 In the course of studies ^8-10 on oxygenation of a Rh(I) complex, [RhCπ(C₈H₁₄)₂]₂, we observed ¹⁰ that a well defined ESR spectrum develops during the reaction in N,N′-dimethylacetamide (DMA) - lithium chloride media. For experimental detail, reference 10 should be consulted. The data summarized in the table refer to the spectrum B in that reference and are attributed to a Rh(II) species.