Series Of Lanthanide Complexes Research Articles

Electronic Structure and Magnetic Anisotropy in Lanthanoid Single-Ion Magnets with C3 Symmetry: The Ln(trenovan) Series.

We report the syntheses and the magnetic characterization of a new series of lanthanide complexes, in which the Ce, Nd, Gd, Dy, Er, and Yb derivatives show single-molecule magnet behavior. These complexes, named Ln(trenovan), where H3trenovan is tris(((3-methoxysalicylidene)amino)ethyl)amine, exhibit trigonal symmetry and the Ln(III) ion is heptacoordinated. Their molecular structure is then very similar to that of the previously reported Ln(trensal) series, where H3trensal is 2,2',2″-tris(salicylideneimino)triethylamine. This prompted us to use the spectroscopic and magnetic properties of the Ln(trensal) family (Ln = Nd, Tb, Dy, Ho, Er, and Tm) to obtain a set of crystal-field parameters to be used as starting point to determine the electronic structures and magnetic anisotropy of the analogous Ln(trenovan) complexes using the CONDON computational package. The obtained results were then used to discuss the electron paramagnetic resonance (EPR) and ac susceptibility results. As a whole, the obtained results indicate for this type of complexes single-molecule magnet behavior is not related to the presence of an anisotropy barrier, due to a charge distribution of the ligand around the lanthanoid, which results in highly mixed ground states in terms of MJ composition of the states. The crucial parameter in determining the slow relaxation of the magnetization is then rather the number of unpaired electrons (only Kramers ions showing in-field slow relaxation) than the shape of the charge distribution for different Ln(III).

A series of lanthanide complexes with different N-donor ligands: synthesis, structures, thermal properties and luminescence behaviors

Complexes 1 and 2 are stitched together via Cl–π and hydrogen bonding interactions to form 1D, 2D, 3D supramolecular structures, while complexes 3 and 4 are packed together by Cl–Cl, π–π, and hydrogen bonding interactions to form 1D, 2D structures.

Optical and relaxometric properties of monometallic (EuIII, TbIII, GdIII) and heterobimetallic (ReI/GdIII) systems based on a functionalized bipyridine-containing acyclic ligand

A series of lanthanide complexes of [LnL(H2O)](2-) composition where Ln = Eu(III), Tb(III) or Gd(III) has been studied for determining their photophysical and relaxometric properties in aqueous solution. The bifunctional ligand L (H5BPMNTA) is an acyclic chelator based on a central functionalized 2,2'-bipyridine core and two iminodiacetate coordinating arms. The mono-aqua Eu(III) and Tb(III) complexes display attractive spectroscopic properties with an excitation wavelength at 316 nm, similar excited state lifetimes and overall quantum yields (in the ranges 0.5-0.6 ms and 10-13%, respectively) in Tris buffer (pH 7.4). The proton longitudinal relaxivity, r1, of the Gd(III) complex is 4.4 mM(-1) s(-1) at 20 MHz and 310 K, which is comparable to that of the clinically used Gd-DTPA (Magnevist®). Interestingly, the water exchange rate between the coordination site and the bulk solvent is very fast (Kex = 2.6 × 10(8) s(-1) at 310 K). The ability of the complex to bind non-covalently to human serum albumin (HSA) was also examined by relaxometric measurements. We also report the synthesis and properties of a bimetallic complex based on Gd-BPMNTA and Re(I)(bpy)(CO)3 components. In this system, the Re core exhibits interesting photophysical properties (λem = 588 nm, Φ = 1.4%) and the Gd-BPMNTA core displays improved relaxivity (r1 = 6.6 mM(-1) s(-1) at 20 MHz and 310 K), due to an increase of the rotational correlation time. Besides these appealing optical and relaxometric properties, the presence of a reactive function on the structure proposes this potential dual imaging probe for conjugation to biomolecules or nanomaterials.

Novel Lanthanide(III) Ternary Complexes with Naphthoyltrifluoroacetone: A Synthetic and Spectroscopic Study

Abstract A series of lanthanide complexes with general formula [Ln(NTA)3X] were prapared [Ln = Y (a), Er (b), Eu (c), NTA = naphthoyltrifluoroacetone, X = H2O (1), phen = phenanthroline (2), bpyO1 = 2, 2′‐bipyridine N‐oxide (3), and bpyO2 = 2, 2′‐bipyridine‐N,N′‐dioxide (4)]. The crystal structures of [Eu(NTA)3bpyO2] (4b), [Er(NTA)3bpyO1] (3c), and [Er(NTA)3phen] (2c) were determined. X‐ray crystallographic analysis reveals that the complexes are of mononuclear structure with three NTA and one ancillary ligand. The photoluminescence spectra of 3c and 4b exhibit strong characteristic emissions arising from Eu3+ central ion due to the efficient sensitization of bpyO1 and bpyO2, respectively.

Synthesis and luminescent spectroscopy of lanthanide complexes with dimethylpyridine-2,6-dicarboxylate (dmpc)

A series of lanthanide complexes with the general formulae [Ln(dmpc)(NO3)2(H2O)2]NO3 (Ln=Pr, Nd, Sm, Eu, Gd, Tb, Dy, and Er) and [La(dmpc)(NO3)2(H2O)2]NO3 were prepared by direct reaction between hydrated lanthanide(III) nitrate and dimethylpyridine-2,6-dicarboxylate (dmpc) in a 1:1 M ratio in ethylacetate–chloroform mixture. The luminescence properties of the dmpc and its Ln(III) complexes were investigated in solid state and in methanol, DMF and DMSO solutions. The Tb–dmpc, Eu–dmpc, Sm–dmpc and Dy–dmpc complexes exhibit characteristic luminescence of Tb(III), Eu(III), Sm(III) and Dy(III) ions indicating energy transfer from the dmpc to the Ln(III) ions. Scavenging activities of the dmpc and its Ln(III) complexes on DPPH• free radical were investigated in DMSO solution at a different concentrations ranges.

Tendency of the Nephelauxetic Effect to Vary in a Series of Lanthanide Complexes with Allyl Acetoacetate

The complexation of allyl acetoacetate with Pr3+, Nd3+, Ho3+, Er3+, and Tm3+ in aqueous solution was studied by electronic absorption spectroscopy. It was shown that allyl acetoacetate at pH 5.50 formed 1:1 and 1:2 complexes with the lanthanide ions depending on the reagent ratio. Intensity parameters Ωλ in addition to bond parameters using the free ions as comparative standards were calculated for the 1:2 complexes. It was established that the nephelauxetic ratio β increased smoothly and approached unity in the order Pr3+ < Nd3+ < Ho3+ < Er3+ < Tm3+. Such variation was explained in the framework of covalent and polarization models.

Synthesis and crystal structure of the new binuclear complex of cerium(III) nitrate with 4,4,10,10-tetramethyl-1,3,7,9-tetraazospiro[5.5]undecane-2,8-dione and the change in the periodical properties in isostructural series of lanthanide complexes with this ligand

The centrosymmetrical binuclar complex of cerium(III) nitrate with bicyclic bis-urea 4,4,10,10-tetramethyl-1,3,7,9-tetraazospiro[5.5]undecane-2,8-dione or spirocarbone (Sk), [Ce(C11H20N4O2)(H2O)2(NO3)3]2 (I), is synthesized for the first time, and its structure is determined (CIF file CCDC 985758). The crystals of compound I are monoclinic: space group P21/n, a = 14.2797(13), b = 7.3922(6), c = 21.003(2) A, β = 102.103(10)°, V = 2167.8(3) A3, ρcalcd = 1.85 g/cm3, Z = 2. The cerium atom is coordinated by two oxygen atoms of two Sk molecules bound by the symmetry procedure (1 − x, −y, 1 − z), three bidentate nitrate anions, and two water molecules. The coordination polyhedron of the cerium atom is an irregular ten-vertex polyhedron. The Ce…Ce distance in the complex is 9.57 A. The change in the periodical properties in a series of the Sk complexes with lanthanide(III) (Ce-Lu, except for Pm) nitrates is discussed.

How strongly are the magnetic anisotropy and coordination numbers correlated in lanthanide based molecular magnets?

Ab initio CASSCF + RASSI-SO investigations on a series of lanthanide complexes [LnIII = Dy(1), Tb(2), Ce(3), Nd(4), Pr(5) and Sm(6)] have been undertaken and in selected cases (for 1, 2, 3 and 4) coordination number (C.N.) around the LnIII ion has been gradually varied to ascertain the effect of C.N. on the magnetic anisotropy. Our calculations reveal that complex 3 possesses the highest barrier height for reorientation of magnetisation (Ueff) and predict that 3 is likely to exhibit Single Molecule Magnet (SMM) behaviour. Complex 5 on the other hand is predicted to preclude any SMM behaviour as there is no intrinsic barrier for reorientation of magnetization. Ground state anisotropy of all the complexes show mixed behaviour ranging from pure Ising type to fully rhombic behaviour. Coordination number around the lanthanide ion is found to alter the magnetic behaviour of all the lanthanide complexes studied and this is contrary to the general belief that the lanthanide ions are inert and exert small ligand field interaction. High symmetric low-coordinate LnIII complexes are found to yield large Ueff values and thus should be the natural targets for achieving very large blocking temperatures.

Structural complexity in the rare earth metallocene hydride complexes, [(C₅Me₅)₂LnH]₂.

X-ray crystallographic data obtained on the metallocene hydrides, [(C5Me5)2LnH]2 (Ln = Gd, Tb, and Dy), of interest for their magnetic properties, have revealed unexpected structural variability in a closely related series of rare earth complexes that can complicate magnetic analysis. Crystals of the two larger metals, Gd and Tb, were structurally straightforward and isomorphous with crystals of [(C5Me5)2SmH]2. However, only for Tb were the locations of the hydride ligands in this structural type identified for the first time and found to be consistent with a (C5Me5)2Ln(μ-H)2Ln(C5Me5)2 structure. In contrast, for Ln = Dy, the [(C5Me5)2H](3-) ligand set does not appear to have one optimum crystal structure. Two different types of crystals and one other solid form of [(C5Me5)2DyH]2 were repeatedly isolated upon crystallization and demonstrated that the structure of any particular crystalline sample selected for magnetic analysis could be variable. Asymmetric structures with a single hydride bridge, (C5Me5)2Dy(μ-H)DyH(C5Me5)2, were identifiable for the two crystalline forms. This demonstrated uncertainty in structure and highlights the importance of having a coordination environment with one preferred form for magnetically interesting complexes.

Crystal structures, antibacterial activity and thermal decomposition kinetics of lanthanide complexes with 4-chloro-2-methoxybenzoic acid and 1,10-phenanthroline

A series of lanthanide complexes [Ln(4-Cl-2-MOBA)3phen]2 (Ln=Sm (1), Nd (2), Ho (3), Eu (4), Dy (5), and Tb (6); 4-Cl-2-MOBA=4-chloro-2-methoxybenzoate, phen=1,10-phenanthroline) were synthesized and characterized. The single-crystal X-ray diffraction demonstrates that 1–3 are isomorphous, which present dimeric structures with four 4-Cl-2-MOBA anions function as bridging ligands. Complexes 1 and 4–6 display their characteristic luminescence emission bands of central Ln3+ ions. The heat capacities, the thermodynamic functions and the thermogravimetry–Fourier transform infrared spectra of gaseous products of complexes 1–6 were investigated. Their non-isothermal kinetics of the second decomposition stage was studied by the integral isoconversional non-linear method and Stark method. Furthermore, 1–6 exhibited excellent antibacterial activity against Candida albicans, Escherichia coli and Staphylococcus aureu.

Structural Rearrangement Through Lanthanide Contraction in Dinuclear Complexes

A new series of lanthanide complexes was synthesized, and the geometry and preliminary magnetic measurements of the complexes were explored. The specific ligand used (N'-(2-hydroxy-3-methoxybenzylidene)benzhydrazide) (H2hmb) was synthesized using a Schiff-base approach and was employed due to the presence of a coordination pocket that is able to accommodate magnetically selective lanthanide ions. The series can be divided into two groups that are categorized by a drastic structural rearrangement. The first group, Type I, contains six analogous complexes with the formula [M(III)2(Hhmb)3(NCS)3]·2MeOH·py (M = Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Ho 6), while the second group, Type II, contains two dinuclear complexes with formula [M(III)2(Hhmb)2(NCS)4(MeOH)2] (M = Er 7, and Yb 8). Single-crystal X-ray analysis revealed that all M(III) ions in Type I exhibit monocapped distorted square antiprismatic geometries, while those of Type II exhibit distorted dodecahedron geometry. The direct current and alternating current magnetic measurements were carried out on all complexes, with 5, 7, and 8 exhibiting slow relaxation of the magnetization under an applied optimum dc field. Furthermore, complex 8 is the first example of a dinuclear Yb-based single-molecule magnet showing field-dependent multiple relaxation processes.

Synthesis, crystal structure and effect of deuterated solvents and temperature on visible and near infrared luminescence of N4-donor Schiff base lanthanide complexes

A series of lanthanide complexes [LnL(NO3)3]·CH3CN [Ln=Ce, (1•Ce); Nd, (2•Nd); Tb, (3•Tb); Dy, (4•Dy); Ho, (5•Ho); Er, (6•Er); Tm, (7•Tm); Yb (8•Yb)] have been synthesized by the reaction of N4 chelate ligand N,N'-bis(2-pyridinylmethylene)cyclohexane-1,2-diamine (L) with lanthanide salts. Photoluminescence spectra of complexes 2•Nd, 3•Tb, 4•Dy, and 8•Yb show the strong characteristic luminescence from visible to near infrared (NIR) region. Further, the singlet state (32,467cm−1) and the lowest triplet (23,202cm−1) energy level of L are calculated, indicating that the energy transfer from L to Tb3+ ion is more effective than that to Dy3+ ion. An extended work is developed to discuss on the effect of deuterated reagent and temperature on luminescent properties of 3•Tb and 8•Yb.

A series of rare earth complexes with novel non-interpenetrating 3D networks: synthesis, structures, magnetic and optical properties

A series of metal-organic framework {Ln(BCPBA)(H2O)}n {Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5)}; {[Ln(BCPBA)(H2O)](H2O)}n {Ln = Pr (6), Gd (7)} have been synthesized through the hydrothermal synthesis method. These compounds possess non-interpenetrating 3D networks with 10.1438 Å× 17.9149 Å rhombic channels along the [001] direction. The results of temperature-dependent magnetic susceptibility measurements indicate that compounds 4 and 7 exhibit Ln(III)Ln(III) antiferromagnetic interactions, while compound 5 exhibits Ln(III)Ln(III) ferromagnetic interactions. Frequency dependent out-of-phase signals were observed in alternating current (ac) magnetic susceptibility measurements which indicate that they have slow magnetic relaxation characteristics. The luminescent properties of 1, 2, 3, 4, and 5 are also discussed. Due to the good match between the lowest triplet state of the ligand and the resonant energy level of the lanthanide ion, compound 4 has longer fluorescence lifetime (τ1 = 400.0000 ms, τ2 = 1143.469 ms) and higher quantum yield (Φ = 42%) compared with other compounds.

Energy transfer in coumarin-sensitised lanthanide luminescence: investigation of the nature of the sensitiser and its distance to the lanthanide ion

A series of lanthanide complexes [Ln(dpxCy)3](3-) have been synthesised. The ligands are composed of a coordinating dipicolinic acid backbone decorated with a polyoxyethylene arm fitted with a coumarin moiety at its extremity. The nature of the coumarin as well as the length of the linker have been varied. Upon excitation at 320 nm, the coumarin exclusively acts as an antenna while the dipicolinic acid core is not excited. Upon excitation below 300 nm, both parts are excited. With europium as a metal centre, the relaxation of the europium ion (intrinsic quantum yield Φ(Eu)(Eu) and radiative lifetime τr) is constant for all the studied ligands. Therefore, the observed differences in overall quantum yield (Φ(Eu)(L)) in such systems come exclusively from the variation of the terminal coumarin. The overall quantum yields of the studied complexes are low (Φ(Eu)(L) < 2% in aqueous solution). In order to rationalise the mechanism of the energy transfer and to improve the sensitisation efficiency (ηsens), the distance between the coumarin sensitiser and the lanthanide centre was explored in solution and compared to the solid state. In the solid state, a dramatic effect was confirmed, with an improvement of 80% in the quantum yield Φ(Eu)(L) for short linkers ((-CH2CH2O-)n with n = 1 compared to n = 3). By monitoring the lifetime decay of the excited state of the lanthanide cation with nanosecond vs. microsecond time-resolved spectroscopy at low temperature, the sensitisation of the lanthanide ions by coumarin derivatives was demonstrated to mainly occur through the singlet excited state of the coumarin and not via the usual triplet pathway. No evidence of a different behaviour at room temperature was found by transient triplet-triplet absorption spectroscopy.

Magnetic Anisotropy and Spin‐Parity Effect Along the Series of Lanthanide Complexes with DOTA

Trendforschung: Beim Wechsel von TbIII- zu YbIII-Zentren der Komplexe des DOTA4−-Liganden wird experimentell beobachtet und theoretisch vorausgesagt, dass sich die Reorientierung der Magnetisierung des apikalen Wassermoleküls ändert, und zwar von senkrecht zu parallel zur Ln-O-Bindung (siehe Bild). Nur Ionen mit einer ungeraden Elektronenzahl zeigen eine langsame Relaxation der Magnetisierung. SMM=Einzelmolekülmagnet.

Magnetic Anisotropy and Spin‐Parity Effect Along the Series of Lanthanide Complexes with DOTA

Spotting trends: Upon going from Tb(III) to Yb(III) centers in the complexes of the DOTA(4-) ligand, a reorientation of the easy axis of magnetization from perpendicular to parallel to the Ln-O bond of the apical water molecule is experimentally observed and theoretically predicted (SMM=single-molecule magnet). Only ions with an odd number of electrons show slow relaxation of the magnetization.

Lanthanide Complexes of the Kläui Metalloligand, CpCo(P═O(OR)2)3: An Examination of Ligand Exchange Kinetics between Isotopomers by Electrospray Mass Spectrometry

A series of lanthanide complexes, {[CpCo(P═O(OR)2)3]2Ln(H2O)x}(+)Cl(-) (Ln = Nd, 3; Eu, 4; Tb, 5; Yb, 6; R = Et, a; R = Ph, b) bearing two cobalt metalloligands were prepared. Electrospray mass spectrometry and thermogravimetric analysis suggest that the cations are either solvent-free or contain very weakly bound water molecules. The related complex {[CpCo(P═O(OPh)2)3]2Yb}(+) [CoCl3(THF)](-), 7, was crystallographically characterized, and the cation in this case was confirmed to be 6-coordinate and solvent-free. Ligand exchange rates between the d0- and d60-isotopomers of 3a-6a and 5b were determined in acetonitrile by electrospray mass spectrometry. The ligand exchange rate was found to increase by almost 4 orders of magnitude from the smallest (Yb, 6a, k = 0.3 M(-1) s(-1)) to largest ion (Nd, 3a, >2500 M(-1) s(-1)) in acetonitrile. Additionally, the ligand exchange rate increased rapidly for 5a (Tb) with increasing water concentration from 30 M(-1) s(-1) in pure acetonitrile to 268 M(-1) s(-1) in 50:50 (v/v) acetonitrile/water. Changing the phosphite substituent had no significant impact on the rate of ligand exchange for 5b (R = Ph) relative to 5a (R = Et).

Microwave-assisted synthesis of lanthanide 2,6-naphthalenedicarboxylates: Thermal, luminescent and sorption characterization

The series of lanthanide complexes with 2,6-naphthalenedicarboxylic acid and DMF molecules was synthesized by the microwave-assisted solvothermal method. The compounds of the general formula Ln2ndc3·nDMF, where Ln=lanthanides from La(III) to Lu(III) (except Pm(III)); ndc2−=C10H6(COO)22− and n=1.5–3 were characterized by the elemental analysis, X-ray diffraction patterns, thermal analysis methods (TG–DSC, TG–FTIR) and infrared spectroscopy. The departure of DMF molecules from the structures occurs in one (Nd), two (Sm–Lu) or several (La–Pr) stages. The photoluminescence properties of the selected complexes in the visible (Eu, Tb) and near-infrared (Nd, Er) spectral regions were investigated. The Eu complex displays intensive red luminescence upon excitation by UV radiation with a long lifetime 1.39 (±0.03) ms whereas the compounds of Nd and Er emit light in the NIR spectral region with the lifetimes of 1.66 (±0.06); 10.13 (±0.08) μs and 2.53 (±0.26); 9.38 (±0.29) μs, respectively. For the Tb complex characteristic metal-based emissions were not observed. Some structural changes were noticed after removal of solvent molecules from the Nd and Er complexes. Porosity of Nd, Tb and Er complexes was investigated on their desolvated forms by nitrogen sorption experiments at 77K. The complexes of Tb and Er displayed real porosity with the BET surface area of 127 and 198m2g−1, respectively whereas nitrogen molecules were not adsorbed by the Nd complex.

Synthesis, characterization, photophysical properties of lanthanide complexes with flexible tripodal carboxylate ligands

Three series of lanthanide complexes [LnL1, LnL2 and LnL3 Ln=Eu, Gd and Tb] have been synthesized with tripodal amide ligands. These ligands have similar benzoate antenna with different substituent groups at para-position (L1=–OME, L2=–H; L3=–CF3). The antenna effect is known to play a prominent role in the luminescence of the lanthanide ions emitting in the coordination complexes. The effect of the ligands triplet and antenna effect have been studied here. The room and low temperature photophysical properties of the nine complexes have been monitored in solution with excitation at 330nm. The emission antenna effect (quantum yield and emission intensity) varied with the triplet state of ligand that comes from the substituent on the benzoate antenna.

Crystal structures and thermodynamic properties of lanthanide complexes with 2-chloro-4,5-difluorobenzoate and 1,10-phenanthroline

A series of lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been synthesized with the formulae of [La(2-cl-4,5-dfba)3phen]n·nH2O (1), [Nd(2-cl-4,5-dfba)3phenH2O]2 (2), [Ln(2-cl-4,5-dfba)3phen]2 (Ln=Eu (3), Ho (4)). The complexes are characterized by elemental analysis, infrared and fluorescent spectra and X-ray single-crystal diffraction. The structures of the four complexes are very different. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror growth pattern. Each La3+ ion is coordinated to four bridging carboxylic groups, two tridentate chelating–bridging carboxylic groups, simultaneous with one phen molecule, giving the coordination number of nine. In the molecular structures of complexes 2 and 3, two Ln3+ ions are linked by four carboxyl groups, forming two binuclear molecules. In addition, each Nd3+ ion in complex 2 is bonded to one H2O molecule and one carboxyl group by monodentate mode, one phen molecule by bidentate chelating, and each Eu3+ ion is also chelated to one phen molecule and one carboxyl group in complex 3. And in complex 4, the Ho3+ ion yields a eight-coordinated distorted square anti-prism coordination geometry. The three-dimensional IR accumulation spectra of gaseous products for complexes 1 to 4 are analyzed and further authenticated the thermal decomposition processes with TG-DTG curves. The heat capacities of complexes 2 to 4 are measured and fitted to a polynomial equation by the least squares method on the basis of the reduced temperature x (x=[T−(Tmax+Tmin)/2]/[(Tmax−Tmin)/2]). Then the smoothed molar heat capacities and thermodynamic functions of complexes 2 to 4 are calculated. The fluorescence intensity of complex 3 is markedly improved as well.