Preparation and properties of lanthanide chelate complexes

Coordination Geometrical Effect on Ligand-to-Metal Charge Transfer-Dependent Energy Transfer Processes of Luminescent Eu(III) Complexes

Photophysical properties of europium (Eu(III)) complexes are affected by ligand-to-metal charge transfer (LMCT) states. Two luminescent Eu(III) complexes with three tetramethylheptadionates (tmh) and pyridine (py), [Eu(tmh)₃(py)₁] (seven-coordinated monocapped-octahedral structure) and [Eu(tmh)₃(py)₂] (eight-coordinated square antiprismatic structure), were synthesized for geometrical-induced LMCT level control. Distances between Eu(III) and oxygen atoms of tmh ligands were estimated using single-crystal X-ray analyses. The contribution percentages of π-4f mixing in HOMO and LUMO at the optimized structure in the ground state were calculated using DFT (LC-BLYP). The Eu-O distances and their π-4f mixed orbitals affect the energy level of LMCT states in Eu(III) complexes. The LMCT energy level of an eight-coordinated Eu(III) complex was higher than that of a seven-coordinated Eu(III) complex. The energy transfer processes between LMCT and Eu(III) ion were investigated using temperature-dependent and time-resolved emission lifetime measurements of ⁵D₀ → ⁷F_J transitions of Eu(III) ions. In this study, the LMCT-dependent energy transfer processes of seven- and eight-coordinated Eu(III) complexes are demonstrated for the first time.

Theoretical study, and infrared and Raman spectra of copper(II) chelated complex with dibenzoylmethane

There are some discrepancies in both the vibrational assignments and in the metal-ligand (M-L) bond strengths predicted in the previous studies on the copper (II) chelated complex of dibenzoylmethane, Cu(dbm)2. Also, there is a lack of theoretical structure, Raman spectrum and full vibrational assignment for Cu(dbm)2 in the literatures. Density functional theory (DFT) at the B3LYP level and also MP2 calculations using different basis sets, besides Natural Bond Orbital (NBO) and Atoms-in-Molecules (AIM) analyses, have been employed to investigate the effect of methyl substitution with the phenyl group on the stabilities of bis(acetylacetonate) copper (II), Cu(acac)2, and Cu(dbm)2 complexes and the electron delocalization in their chelated rings. Measured solid phase infrared and Raman bands for Cu(dbm)2 complex have been interpreted in terms of the calculated vibrational modes and detailed assignment has been presented. We concluded that, theoretically, the results of charge transfer studies, and experimentally, in-phase symmetric O-Cu-O stretching mode of these complexes are very useful measures for M-L bond strength. The electron delocalization in the chelated rings and the M-L bond strength in Cu(dbm)2 are concluded to be higher than those in Cu(acac)2. The calculated geometries and vibrational results are in good agreement with the experimental data.

Europium(III) complexes containing organosilyldipyridine ligands grafted on silica nanoparticles

This work focuses on the grafting of transition metal complexes on silica surface nanoparticles. Nanoscale silica particles in aqueous sols are used as starting silicated materials. We have undertaken the synthesis of europium(III) complexes containing organosilyldipyridine ligands, (EtO)3Si(CH2)3NHCH2-bipy (1) and (EtO)(CH3)2Si(CH2) 3NHCH 2-bipy (2), in view of a direct grafting reaction on silica nanoparticles. Reaction of one molar equivalent of 1 and 2 with Eu(tmhd)3 (tmhd= 2,2,6,6-tetramethyl-3,5-heptanedionato), as precursor, leads to octacoordinated silylated europium(III) complexes [Eu(tmhd)3(1)] (3) and [Eu(tmhd)3(2)] (4) as white solids in 34-54% yields. Europium complexes were characterized by elemental analysis, mass spectrometry, FT-IR, UV, and luminescence spectroscopies. These new complexes are reacting in a 1:10 (v/v) water and ethanol mixture with silica nanoparticles colloidal sol. Elemental analysis and thermogravimetric data indicated grafting ratios of 0.41 and 0.26 mmol of europium(III) complexes per gram of silica. Functionalized silica nanoparticles were characterized by DRIFT spectroscopy and TEM microscopy. The first analysis shows that the chemical integrity of the complexes is retained on the silica surface together with the size and the monodispersity of the nanoscale particles. As expected for europium(III) complexes, luminescence is observed under UV irradiation. Emission and excitation spectra indicate that the metal coordination environment is not modified on the silica surface. Moreover, the sharpness of the luminescence bands and the strong antenna effect are maintained when complexes are covalently bonded to silica. New luminescent europium(III) complexes grafted on silica nanoparticles are therefore obtained from our approach.

Optical absorption spectroscopic studies on holmium(III) complexes with beta-diketone and heterocyclic amines: the environment effect on 4f-4f hypersensitive transitions

The optical absorption spectra of [Ho(acac)(3)(H(2)O)(2)].H(2)O, [Ho(acac)(3)phen] and [Ho(acac)(3)bpy] (where acac is the anion of acetylacetone; phen is 1,10-phenanthroline and bpy is 2,2'-bipyridyl) complexes in the visible region, in a series of non-aqueous solvents (methanol, ethanol, isopropanol, chloroform, acetonitrile and pyridine.) have been analyzed. The largest intensity variation was observed in the (5)G(6)<--(5)I(8) (centered at 450 nm), and (5)G(5), (3)H(5), (3)H(6)<--(5)I(8) (centered at 360 nm) transition regions. The band shape and oscillator strength of the hypersensitive transitions display pronounced changes as compared to Ho(3+) aqua-ion. The band shapes of the hypersensitive transitions show remarkable changes on passing from aqueous solution to various non-aqueous solutions which is the result of change in the environment about the Ho(III) ion in the various solutions and suggests coordination of solvent molecule(s), in some cases. The results clearly show that among the solvents studied pyridine is the most effective in promoting the 4f-4f spectral intensity. It has been inferred from this study that 2,2'-bipyridyl is a stronger ligand for heavier lanthanides. A comparative account of hypersensitivity in the present complexes with those of other adducts of Ho(beta-diketoenolate)(3) with heterocyclic amines is discussed. The TGA analyses showed that the phen complex is thermally more stable over its bpy analogue.

Nuclear magnetic resonance and optical absorption spectroscopic studies on paramagnetic praseodymium(III) complexes with beta-diketone and heterocyclic amines

The optical absorption spectra of [Pr(acac)(3)(H(2)O)(2)].H(2)O, [Pr(acac)(3)phen.H(2)O] and [Pr(acac)(3)bpy] (where acac is the anion of acetylacetone, phen is 1,10-phenanthroline and bpy is 2,2'-bipyridyl) have been analyzed in the visible region in a series of non-aqueous solvents (methanol, ethanol, isopropanol, chloroform, acetonitrile and pyridine). The complexes display four non-hypersensitive 4f-4f transitions ((3)P(2), (3)P(1)+(1)I(6), (3)P(0) and (1)D(2)) from the (3)H(4) ground state. The band shape of the transitions shows remarkable changes upon dissolving in different solvents. Distinctively different band shapes have been observed for phen and bpy complexes. The phen is more effective in producing changes and the splitting of the bands is more pronounced in phen complex since it is a stronger ligand and leads to stronger Pr-N(phen) bond. The splitting of the bands is indicative of partaking of f-orbitals in bonding. The NMR signals of heterocyclic amines have been shifted to high fields while the resonances due to acetylacetone moiety have moved to low fields which is the consequence of change in geometry of the complexes upon coordination of the heterocyclic amines and reflects the importance of geometric factor (3cos(2)theta-1) in changing sign of the shift and to a good approximation the shifts arise predominantly from the dipolar mechanism. The phen complexes have narrower line width than bpy complexes. The line broadening in the case of bpy complexes is suggestive of exchange between inter-converting forms. The bpy possesses some degree of rotational freedom about C(6)-C(6') bond and the two pyridine rings undergo scissoring motion with respect to each other.