Series Of Ln Research Articles

Trends in Hamiltonian parameters determined by systematic analysis of f-d absorption spectra of divalent lanthanides in alkali-halides hosts: II. CaCl2:Ln2+ (Ln = Sm, Eu, Tm, and Yb)

Systems containing divalent lanthanide elements (Ln2+) are hard to synthesize and thus their characterization is still largely an unexplored area. The absorption spectra of most divalent Ln2+ ions were, until recently, obtained nearly exclusively for Ln2+:CaF2 crystals. In the first paper in a series devoted to systematic analysis of f-d absorption spectra of Ln2+ in alkali-halides hosts we presented new experimental data for Nd2+ and Dy2+ ions in SrCl2 and reanalyzed available data for SrCl2: Ln2+ (Ln = Sm, Eu, Tm, and Yb). The increased number of spectral data on the f-d transitions for Ln2+ ions makes SrCl2 the second best studied matrix. The second paper in this series is devoted to CaCl2:Ln2+ (Ln = Sm, Eu, Tm, and Yb). The first absorption, emission, and excitation spectra for Sm2+, Eu2+ and Yb2+ in CaCl2 are reported. Using a uniform methodology based on a parametric Hamiltonian model proposed in Part I, a systematic analysis of the spectra is performed. This approach yields refined and consistent sets of the free-ion parameters and crystal-field (CF) ones. Systematic CF analysis of the large spectral dataset for CaCl2:Ln2+ consisting of a total of four ions allows revealing inherent trends across the Ln series. Our results enable partial verification of the trends uncovered in Part I for Ln2+:SrF2. It appears that the trends in the free-ion parameters and, to a lesser extent, CF ones observed for one Ln2+ ion are sufficiently systematic to allow for tentative predictions of the spectrum for any lanthanide ion based on the sets of parameters derived from the spectra obtained for another ion in the same matrix.

Construction of metal–organic frameworks (MOFs) and highly luminescent Eu(iii)-MOF for the detection of inorganic ions and antibiotics in aqueous medium

A series of Ln(iii) complexes were synthesized. The highly luminescent chemically stable Eu-MOF shows multi-responsive luminescence sensing functions.

A series of Ln2 complexes based on an 8-hydroxyquinoline derivative: slow magnetization relaxation and photo-luminescence properties

A series of Ln2 complexes display slow magnetization relaxation and photo-luminescence properties.

Weak interactions cause selective cocrystal formation of lanthanide nitrates and tetra-2-pyridinylpyrazine

Two series of cocrystals Ln(NO3)5·H2TPPZ are synthesized enlightening the lanthanide contraction effect and weak hydrogen bonding interactions in determining the selective cocrystallization, stability and energy transfer for luminescence.

Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters

A series of three isostructural tetranuclear complexes with the general molecular formula [Ln4(μ3-OH)4(L)4(μ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH'3) led to the isolation of dinuclear Ln(iii) complexes with the general molecular formula [Ln2(L)4(μ2-LH'2)2]·4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1-6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J1 = -0.055 cm-1 and g = 2.01) extracted by fitting χMT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J1 = -0.048 cm-1 and g = 1.99) between the Gd(iii) ions, the χMT(T) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(iii) and Tb(iii) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (Ueff) of 38.17 cm-1 with a pre-exponential factor (τ0) of 1.85 × 10-6 s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (-ΔSm) of 1 and 4 was found to be 25.57 J kg-1 K-1 and 12.93 J kg-1 K-1, respectively, at 3.0 K for ΔH = 70 kOe.

Stoichiometric control: 8- and 10-coordinate Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 complexes of the early lanthanides La-Sm.

The coordination sphere of early lanthanide(iii) ions is highly versatile, exhibiting the ability to form 8-, 9-, and 10-coordinate complexes with the same ligand set. The ability to isolate 10-coordinate complexes decreases across the period, and the late lanthanides typically cannot support a coordination number higher than eight. Using two common, commercially available ligands, hfac (1,1,1,5,5,5-hexafluoroacetylacetonato-) and bpy (2,2'-bipyridine), the 8- and 10-coordinate series Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 (Ln = La-Sm) are compiled in a single investigation, demonstrating that the desired coordination number can be targeted through stoichiometry. Solvent-free syntheses of Ln(hfac)3(bpy) and Ln(hfac)3(bpy)2 complexes from Ln(hfac)3(H2O)3 precursors are investigated using a mechanochemical approach. Structural and spectroscopic properties as well as melting point trends are reported for the series.

Controlled Synthesis, Evolution Mechanisms, and Luminescent Properties of ScFx:Ln (x = 2.76, 3) Nanocrystals

Kinetic or thermodynamic control has been employed to guide the selective synthesis of conventional organic compounds, and it should be a powerful tool as well for accessing unusual inorganic nanocrystals, particularly when a series of members with similar chemical compositions and phase structures exist. Indeed, a comprehensive mapping of the energy barrier distribution of each nanocrystal in a predefined reaction system will enable not only the precise synthesis of nanocrystals with expected sizes, morphologies, phase structures, and ultimately functionalities, but also disclosure of the evolution details of nanocrystals from one structure to another. Using ScFx:Ln (x = 2.76, 3) series as a proof-of-concept, we have successfully mapped out the energy barriers that correspond to each of the ScFx:Ln nanocrystals, unraveled suitable temperatures for each type of nanocrystal formation, recorded their phase transition procedures, and also discovered the relationships of the products at each reaction stage. T...

Tuning Intrinsic and Extrinsic Proton Conduction in Metal-Organic Frameworks by the Lanthanide Contraction.

Seven isomorphous lanthanide metal-organic frameworks in the PCMOF-5 family, [Ln(H5L)(H2O)n](H2O) (L = 1,2,4,5-tetrakis(phosphonomethyl)benzene, Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) have been synthesized and characterized. This family contains 1-D water-filled channels lined with free hydrogen phosphonate groups and gives a very low activation energy pathway for proton transfer. The lanthanide contraction was employed to systematically vary the unit cell dimensions and tune the proton conducting pathways. LeBail fitting of the crystalline series shows that the crystallographic a-axis, along the channel, can be varied in increments less than 0.02 Å correspondingly shortening the proton transfer pathway. The proton conductivities for the La and Pr complexes were roughly an order of magnitude higher than other members of the series (10-3 S cm-1 versus 10-4 S cm-1). Single crystal structures of the high and low conducting members of the series (La, Pr for high and Ce for low) affirm the structural similarities extend beyond the unit cell parameters to positions of free acid groups and included water molecules. Scanning electron microscopy reveals marked differences in particle size of the different members of the Ln series owing to lattice strain effects induced by changing the lanthanide. Notably, the high conducting La and Pr complexes have the largest particle sizes. This result contradicts any notion that degradation of the MOF at grain boundaries is enabling the observed conductivity as proton conduction dominated by extrinsic pathways would be enabled by small particles (i.e., the La and Pr complexes would be the worst conductors). Proton conductivity measurements of a ball milled sample of the La complex corroborate this result.

Structure of lanthanum(III) tris-dipivaloylmethanate

A series of Ln(III) dipivaloylmethanates of the composition Ln(dpm)3 (Ln = La, Tm, Yb) is obtained. It is established that Tm(dpm)3 and Yb(dpm)3 complexes are isostructural with Lu(dpm)3. The crystal structure of [La(dpm)3]2 at 150(2) K is determined (space group P21/n, a = 12.4412(5) A, b = 28.0579(12) A, с = 21.9533(8) A, β = 105.796(2)°, V = 7373.9(5) A3, Z = 4). The studied compound is isostructural with [Pr(dpm)3]2, [Eu(dpm)3]2, [Gd(dpm)3]2, and [Tb(dpm)3]2 complexes. The crystal structure of the complex is formed by dimeric [La(dpm)3]2 molecules. Thermogravimetric investigations show that the volatility of Ln(dpm)3 increases in the series from [La(dpm)3]2 to Yb(dpm)3. Melting points of the complexes are close to the known literature data.

Formation of W/O Microemulsions in the Extraction of the Lanthanide Series by Purified Cyanex 301

ABSTRACTThe formation of water-in-oil (W/O) microemulsions during the extraction of the series of trivalent lanthanides Ln(III) by bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301, also known as purified Cyanex 301) was studied. The phenomena in the formation of W/O microemulsions were similar in the extraction of all Ln(III) by HC301 at a high neutralization degree (50%), according to the measurement of the distribution ratios of Ln(III) and the concentrations of Na+ and NO3- in the organic phase, IR spectroscopy, and dynamic light scattering (DLS). W/O microemulsions also formed at a low neutralization degree (15%) for the extraction of heavy Ln(III). The coordination environment of the representative heavy lanthanide Ho(III) in the extracted complexes was monitored by absorption spectroscopy and extended X-ray absorption fine structure (EXAFS). Unlike the light lanthanide, Nd(III) and Ho(III) in the organic phase did not directly coordinate with the HC301 anions regardless of whether W/O microemulsions formed, which further demonstrated the different extraction behavior of HC301 toward the light lanthanides and the heavy lanthanides.

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).

Bis(salicylato)borate as Versatile Sensitizer for Highly Luminescent Lanthanide Oxoborates from the Ultraviolet to Near Infrared with 4f and 5d Participation of the Lanthanides

Several lanthanide bis(salicylato)borate (BSBs) compounds were synthesized from anhydrous lanthanide chlorides and pyridine (py). The reactions start with the formation of small complexes, as indicated by [ErCl2(py)4(BSB)], on to 1D polymers 1∞[Ln(BSB)3(py)2] (Ln = Y, La–Nd, Sm) with a reduced py content. As the lanthanide radii contract along the lanthanide (Ln) series, the formation of 2D networks of the constitution 2∞[Ln(BSB)3(py)] (Ln = Sm, Eu, Tb, Dy, Er) is observed with the further release of py. The coordination polymers exhibit intense photoluminescence from the UV to the near‐infrared (NIR) region through lanthanide‐specific 4f–4f emission for the Nd3+, Sm3+, Eu3+, Tb3+, and Dy3+ species. The emission is remarkable for the Dy3+ (yellow‐white) and Nd3+ (NIR) species owing to the sensitizer effects of the [BSB]– anion, which shows energy transfer to most Ln ions. For the Ce3+ species, the participation of 5d states is observed and produces parity‐allowed broadband 5d–4f emission. The bis(salicylato)borate ligand shows fluorescence in the UV with a short lifetime of only 2 ns, which makes the energy transfer in the other Ln compounds remarkable and marks it as versatile sensitizer for these metal ions.

Microporous Hexanuclear Ln(III) Cluster-Based Metal-Organic Frameworks: Color Tunability for Barcode Application and Selective Removal of Methylene Blue.

Two hexanuclear Ln(III) cluster-based metal-organic frameworks (MOFs) (Ln = Tb or Eu) and a series of isomorphic bimetallic Ln(III)-MOFs have been synthesized by changing the ratio of Tb(III) and Eu(III) under solvothermal conditions. The excellent linear color tunability (from green to red) makes them suitable for barcode application. In addition, the anionic Ln(III)-MOFs exhibit superior uptake capacity toward methylene blue (MB+) by an ion-exchange process, and its reversible adsorption performance makes 1 suitable for removal of organic dye MB+. The as-prepared anionic hexanuclear Ln(III) cluster-based MOFs can serve as a multifunctional material for an optical and environmental area.

Theoretical Study on the Photoelectron Spectra of Ln(COT)2–: Lanthanide Dependence of the Metal–Ligand Interaction

We have performed a theoretical analysis of the recently reported photoelectron (PE) spectra of the series of sandwich complex anions Ln(COT)2- (Ln = La-Lu, COT = 1,3,5,7-cyclooctatetraene), focusing on the Ln dependence of the vertical detachment energies. For most Ln, the π molecular orbitals, largely localized on the COT ligands, have the energy order of e1g < e1u < e2g < e2u as in the actinide analogues, reflecting the substantial orbital interaction with the Ln 5d and 5p orbitals. Thus, it would be expected that the lanthanide contraction would increase the orbital interaction so that the overlaps between the COT π and Ln atomic orbitals tend to increase across the series. However, the PE spectra and theoretical calculations were not consistent with this expectation, and the details have been clarified in this study. Furthermore, the energy level splitting patterns of the anion and neutral complexes have been studied by multireference ab initio methods, and the X peak splittings observed in the PE spectra only for the middle-range Ln complexes were found to be due to the specific interaction between the Ln 4f and ligand π orbitals of the neutral complexes in e2u symmetry. Because the magnitude of this 4f-ligand interaction depends critically on the final state 4f electron configuration and the spin state, a significant Ln dependence in the PE spectra is explained.

Emissive mononuclear Eu(III) and Tb(III) complexes bearing deprotonated 2,2′-bipyridyl-1,2,4-triazole terdentate ligands

A series of new emissive mononuclear Ln(III) complexes with deprotonated 2,2ʹ-bipyridyl-1,2,4-triazole terdentate ligands, [Ln(L)(DMF)2(NO3)2]∙n(solvent) (Ln = Eu (1 and 2), Tb (3 and 4), HL = 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-2,2′-bipyridine, 6-(5-trifluoromethyl-1,2,4-triazol-3-yl)-4,4′-dimethyl-2,2′-bipyridine), have been synthesized and characterized. As revealed by X-ray crystallography, each Ln(III) has a distorted tricapped trigonal prism generated by three nitrogens from one 2,2ʹ-bipyridyl-1,2,4-triazolate chelate and six oxygens from two DMF molecules and two chelating nitrates, where 2,2ʹ-bipyridyl-1,2,4-triazole serves as a mono-anionic tridentate chelate via deprotonation of the 1,2,4-triazolyl-NH. Complexes 1–4 are all emissive at room temperature in solution and solid states, and the introduction of two methyl groups into the 2,2ʹ-bipyridyl ring is efficient in enhancing luminescence efficiencies of Ln(III) complexes.

Topological Study of Bonding in Aquo and Bis(triazinyl)pyridine Complexes of Trivalent Lanthanides and Actinides: Does Covalency Imply Stability?

The geometrical and electronic structures of Ln[(H2O)9]3+ and [Ln(BTP)3]3+, where Ln = Ce-Lu, have been evaluated at the density functional level of theory using three related exchange-correlation (xc-)functionals. The BHLYP xc-functional was found to be most accurate, and this, along with the B3LYP functional, was used as the basis for topological studies of the electron density via the quantum theory of atoms in molecules (QTAIM). This analysis revealed that, for both sets of complexes, bonding was almost identical across the Ln series and was dominated by ionic interactions. Geometrical and electronic structures of actinide (An = Am, Cm) analogues were evaluated, and [An(H2O)9]3+ + [Ln(BTP)3]3+ → [Ln(H2O)9]3+ + [An(BTP)3]3+ exchange reaction energies were evaluated, revealing Eu ↔ Am and Gd ↔ Cm reactions to favor the An species. Detailed QTAIM analysis of Eu, Gd, Am, and Cm complexes revealed increased covalent character in M-O and M-N bonds when M = An, with this increase being more pronounced in the BTP complexes. This therefore implies a small electronic contribution to An-N bond stability and the experimentally observed selectivity of the BTP ligand for Am and Cm over lanthanides.

Structure and Magnetocaloric Effect of Two Kinds of Ln–MnII Heterometallic Coordination Polymers Produced by Fractional Crystallization

Two series of Ln–MnII heterometallic coordination polymers (HCPs), [Ln8Mn3(µ3‐OH)8(IN)14Cl6(H2O)16]n(OH)2n·5nDMF·8nH2O {Ln = Gd (1); Ln = Dy (2)} and [Ln2Mn(IN)6Cl2(H2O)4]n·2nDMF {Ln = Gd (3); Ln = Dy (4), IN = isonicotinic cation}, were synthesized by using fractional crystallization and structurally characterized. Polymers 1 and 2 are isostructural and form a 2D double layer of [Ln4(µ3‐OH)4] cubane and Mn(IN)4Cl2 units, whereas 3 and 4 are isomorphic and form a four‐connected cds‐type 3D framework assembled from paddle‐wheel binuclear Ln2(COO)4 units and planar Mn(IN)4Cl2 units. Polymers 1–4 exhibited large magnetic entropy changes of 42.0, 16.7, 31.5, and 16.6 J kg–1 K–1, respectively (ΔH = 7 T). In addition, compounds 2 and 4 displayed field‐induced slow magnetic relaxation behavior.

Ce/Au(CN)2–‐Based Coordination Polymers Containing and Lacking Aurophilic Interactions

AbstractNew members of the Ln[Au(CN)2]3·3H2O and [nBu4N]2[Ln(NO3)4Au(CN)2] series Ln = Ce (CeAu3 and CeAu respectively) are reported herein where their synthesis, structure and photoluminescence properties are discussed. The first is a 3‐D coordination polymer with aurophilic interactions of 3.35 Å and the latter is a 1‐D coordination polymer that lacks them. At 293 K both CeAu3 and CeAu display characteristic CeIII‐based emission at λmax = 393 nm (5d→2FJ), however in CeAu3 AuI‐based emission (λmax = 410, 1MLCT) dominates the spectrum. At 77 K however, the dominant emission is AuI‐based with characteristic emissions of λmax = 430 nm (1MLCT) and 490 nm (3MLCT). The key difference in the luminescence of these two materials can be rationalized in terms of their respective structures, through either the aurophilic network and lack thereof and/or the rigidity offered in the 3‐D structure of CeAu3.

Non-parametric and least squares Langley plot methods

Abstract. Langley plots are used to calibrate sun radiometers primarily for the measurement of the aerosol component of the atmosphere that attenuates (scatters and absorbs) incoming direct solar radiation. In principle, the calibration of a sun radiometer is a straightforward application of the Bouguer–Lambert–Beer law V = V0e−τ ⋅ m, where a plot of ln(V) voltage vs. m air mass yields a straight line with intercept ln(V0). This ln(V0) subsequently can be used to solve for τ for any measurement of V and calculation of m. This calibration works well on some high mountain sites, but the application of the Langley plot calibration technique is more complicated at other, more interesting, locales. This paper is concerned with ferreting out calibrations at difficult sites and examining and comparing a number of conventional and non-conventional methods for obtaining successful Langley plots. The 11 techniques discussed indicate that both least squares and various non-parametric techniques produce satisfactory calibrations with no significant differences among them when the time series of ln(V0)'s are smoothed and interpolated with median and mean moving window filters.

A Pyridine-Based Ligand with Two Hydrazine Functions for Lanthanide Chelation: Remarkable Kinetic Inertness for a Linear, Bishydrated Complex.

To study the influence of hydrazine functions in the ligand skeleton, we designed the heptadentate HYD ligand (2,2',2″,2‴-(2,2'-(pyridine-2,6-diyl)bis(2-methylhydrazine-2,1,1-triyl)) tetraacetic acid) and compared the thermodynamic, kinetic, and relaxation properties of its Ln(3+) complexes to those of the parent pyridine (Py) analogues without hydrazine (Py = 2,6-pyridinebis(methanamine)-N,N,N',N'-tetraacetic acid). The protonation constants of HYD were determined by pH-potentiometric measurements, and assigned by a combination of UV-visible and NMR spectroscopies. The protonation sequence is rather unusual and illustrates that small structural changes can strongly influence ligand basicity. The first protonation step occurs on the pyridine nitrogen in the basic region, followed by two hydrazine nitrogens and the carboxylate groups at acidic pH. Contrary to Py, HYD self-aggregates through a pH-dependent process (from pH ca. 4). Thermodynamic stability constants have been obtained by pH-potentiometry and UV-visible spectrophotometry for various Ln(3+) and physiological cations (Zn(2+), Ca(2+), Cu(2+)). LnHYD stability constants show the same trend as those of LnDTPA complexes along the Ln(3+) series, with log K = 18.33 for Gd(3+), comparable to the Py analogue. CuHYD has a particularly high stability (log K > 19) preventing its determination from pH-potentiometric measurements. The stability constant of CuPy was also revisited and found to be underestimated in previous studies, highlighting that UV-visible spectrophotometry is often indispensable to obtain reliable stability constants for Cu(2+) chelates. The dissociation of GdL, assessed by studying the Cu(2+)-exchange reaction, occurs mainly via an acid-catalyzed process, with limited contribution from direct Cu(2+) attack. The kinetic inertness of GdHYD is remarkable for a linear bishydrated chelate; the 25-fold increase in the dissociation half-life with respect to the monohydrated commercial contrast agent GdDTPA (t1/2 = 5298 h for GdHYD vs 202 h for GdDTPA) is related to the rigidity of the HYD ligand due to the pyridine and methylated hydrazine functions of the backbone. A combined analysis of variable-temperature (17)O NMR and NMRD data on GdHYD yielded the microscopic parameters influencing relaxation properties. The high relaxivity (r1 = 7.7 mM(-1) s(-1) at 20 MHz, 25 °C) results from the bishydrated character of the complex combined with an optimized water exchange rate (kex(298) = 7.8 × 10(6) s(-1)). The two inner-sphere water molecules are not replaced through interaction with biological cations such as carbonate, citrate, and phosphate as monitored by (1)H relaxivity and luminescence lifetime measurements.