Holmium Complexes Research Articles

Synthesis and Crystal Structure of a New Dinuclear Holmium(III) Complex with a Bulky Anthracene-Based Carboxylate Ligand

The reaction of Ho(NO3)3 with the bulky anthracene-9-carboxylic acid (HL) and 1,10-phenanthroline (phen) in the presence of 2,6-dimethylpyridine afforded a dinuclear HoIII complex [Ho2(L)6(phen)2] (1) (L = anthracene-9-carboxylate), which was characterized by elemental analysis and single-crystal X-ray diffraction analysis (triclinic system, space group Pī, with a = 12.4994(3), b = 13.3556(3), c = 14.9751(3) A, α = 110.7630(1), β = 103.0680(1), γ = 106.8530(1)°, V = 2080.59(9) A3, and Z = 1). Complex 1 has a centrosymmetric binuclear cage structure in which two HoIII atoms are both nine-coordinated and bridged by four bulky anthracnene-9-carboxylate (L) ligands with a non-bonding Ho∙∙∙Ho separation of 3.9076 (2) A. The anthracene-9-carboxylate groups coordinate each HoIII atom in three different ways. The adjacent discrete dinuclear subunits are arranged into a one-dimensional (1D) chain along the [111] direction by intermolecular π···π stacking interactions, with the centroid–centroid separation of 3.724(2) A. A dinuclear HoIII complex has been successfully achieved by using a bulky anthracene-9-carboxylic acid (HL), together with incorporating 1,10-phenanthroline (phen) as a chelating co-ligand. This work offers a new proof of the coordination versatility of simple monocarboxylic acid ligands bearing a bulky aromatic skeleton.

Design Principles and Theory of Paramagnetic Fluorine‐Labelled Lanthanide Complexes as Probes for 19F Magnetic Resonance: A Proof‐of‐Concept Study

The synthesis and spectroscopic properties of a series of CF(3)-labelled lanthanide(III) complexes (Ln=Gd, Tb, Dy, Ho, Er, Tm) with amide-substituted ligands based on 1,4,7,10-tetraazacyclododecane are described. The theoretical contributions of the (19)F magnetic relaxation processes in these systems are critically assessed and selected volumetric plots are presented. These plots allow an accurate estimation of the increase in the rates of longitudinal and transverse relaxation as a function of the distance between the Ln(III) ion and the fluorine nucleus, the applied magnetic field, and the re-rotational correlation time of the complex, for a given Ln(III) ion. Selected complexes exhibit pH-dependent chemical shift behaviour, and a pK(a) of 7.0 was determined in one example based on the holmium complex of an ortho-cyano DO3A-monoamide ligand, which allowed the pH to be assessed by measuring the difference in chemical shift (varying by over 14 ppm) between two (19)F resonances. Relaxation analyses of variable-temperature and variable-field (19)F, (17)O and (1)H NMR spectroscopy experiments are reported, aided by identification of salient low-energy conformers by using density functional theory. The study of fluorine relaxation rates, over a field range of 4.7 to 16.5 T allowed precise computation of the distance between the Ln(III) ion and the CF(3) reporter group by using global fitting methods. The sensitivity benefits of using such paramagnetic fluorinated probes in (19)F NMR spectroscopic studies are quantified in preliminary spectroscopic and imaging experiments with respect to a diamagnetic yttrium(III) analogue.

Effect of silver nanoparticles on the dielectric properties of holmium doped silica glass

The effect of silver nanoparticle co-doping on the dielectric properties of holmium doped silica glasses was studied. Silver nanoparticles of size between 20 and 22 nm were produced by the sol–gel technique. One of the samples showed an icosahedral morphology of the nanocrystal formed, along with spherical morphology. It was found that the tuning of the dielectric constant values could be accomplished by co-doping. The sample, with 1 wt% of Ho, had low dielectric constant values within the range 100 Hz–3 MHz due to the formation of quasi-molecular structures of holmium. This effect was evaded to some extent with silver co-doping as a result of the interdispersion of holmium complexes. Also it was found that the co-doping produced a higher dielectric loss which was calculated from the tan δ–log f graph. The Cole–Cole parameters and the Jonscher power law parameters were also calculated and are presented.

Chemical, radiochemical and biological studies of Sm and Ho complexes of H4dota analogues containing one methylphosphonic/phosphinic acid pendant arm

AbstractThis work intends to investigate samarium and holmium complexes with a set of H4dota‐analogues bearing methylphosphonate/methylphosphinic acid pendant arms (H5do3ap, H5do3apPrA and H4do3apABn) as new bifunctional ligands for radiolanthanide targeted therapy. Radiolanthanide complexes of these ligands were prepared and evaluated and thermodynamic solution studies were also performed to get a better insight on the radiochemical results. The radiocomplexes were quantitatively prepared, are hydrophilic and negatively charged. They present a high in vitro and in vivo stability, a low plasma protein binding and a rapid clearance from the main organs with a high rate of whole body radioactivity excretion. Stability constants with Sm(III) and Ho(III) were determined by potentiometry and the values found are very high for all the ligands. Actually, they are similar to those of H4dota for the phosphinate analogues and even higher for the phosphonate ligand, being the constants similar to those with other lanthanide(III) ions. The effect of methylphosphorus acid pendant arms functionalization and the use of these ligands as bifunctional chelate agents are discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Poly[(6-carboxypicolinato-κ3O2,N,O6)(μ3-pyridine-2,6-dicarboxylato-κ5O2,N,O6:O2′:O6′)dysprosium(III)

In the title complex, [Dy(C7H3NO4)(C7H4NO4)]n, one of the ligands is fully deprotonated while the second has lost only one H atom. Each DyIII ion is coordinated by six O atoms and two N atoms from two pyridine-2,6-dicarboxyl­ate and two 6-carboxy­picolinate ligands, displaying a bicapped trigonal-prismatic geometry. The average Dy—O bond distance is 2.40 Å, some 0.1Å longer than the corresponding Ho—O distance in the isotypic holmium complex. Adjacent DyIII ions are linked by the pyridine-2,6-dicarboxyl­ate ligands, forming a layer in (100). These layers are further connected by π–π stacking inter­actions between neighboring pyridyl rings [centroid–centroid distance = 3.827 (3) Å] and C—H⋯O hydrogen-bonding inter­actions, assembling a three-dimensional supra­molecular network. Within each layer, there are other π–π stacking inter­actions between neighboring pyridyl rings [centroid–centroid distance = 3.501 (2) Å] and O—H⋯O and C—H⋯O hydrogen-bonding inter­actions, which further stabilize the structure.

Imidophosphinate complexes of lanthanides. Investigation of thermochemical properties

New imidodiphosphinate complexes of neodymium and holmium of the general formula Ln[Ph2P(O)NP(O)Ph2]3 were synthesized. Results of investigation of their properties by means of differential scanning calorimetry, mass spectrometry, and the effusive Knudsen method are presented. Thermodynamic parameters of melting and sublimation are calculated.

Holmium porphyrin compound liquid crystals: Synthesis and properties

5,10,15,20-Tetra-[(p-alkoxy-m-ethyloxy)phenyl]porphyrin and [5-(p-alkoxy)phenyl-10,15,20-tri-phenyl]porphyrin and their holmium(III) complexes are reported. They display a hexagonal columnar discotic columnar (Col h) liquid crystal phase and were studied by cyclic voltammetry, surface photovoltage spectroscopy (SPS), electric-field-induced surface photovoltage spectroscopy (EFISPS) and luminescence spectroscopy. Within the accessible potential window, all these compounds exhibit two one-electron reversible redox reactions. Quantum yields of Q band are in the region 0.0045–0.21 at room temperature. The SPS and EFISPS reveal that all the compounds are p-type semiconductors and exhibit photovoltaic response due to π–π ∗ electron transitions.

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

The optical absorption spectra of [Ho(acac) 3(H 2O) 2]·H 2O, [Ho(acac) 3phen] and [Ho(acac) 3bpy] (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 5G 6 ← 5I 8 (centered at 450 nm), and 5G 5, 3H 5, 3H 6 ← 5I 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(β-diketoenolate) 3 with heterocyclic amines is discussed. The TGA analyses showed that the phen complex is thermally more stable over its bpy analogue.

Generation of Dimethylsilylene and Allylidene Holmium Complexes from Trimethylsilylated Allyl Ligands

The reaction of K[1,3-(SiMe3)2C3H3] with partially hydrated holmium triflate leads to a dimeric complex (1) in which hydrogen abstraction from a trimethylsilyl group has occurred on two allyl ligands, forming dimethylsilylene units that bridge the holmium atoms. When the reaction time is prolonged, a different product (2) is isolated, in which in addition to two dimethylsilylene bridges, the metal centers are joined with a mu-eta1,eta3-allylidene ligand. Both crystallographic and computational studies provide evidence for delocalized bonding in the allylidene fragment.

Synthesis and Characterization of Yttrium(III), Lanthanum(III), and Holmium(III) Complexes with a Heptadentate Schiff Base Ligand

Yttrium(III), lanthanum(III), and holmium(III) complexes with tris‐(salicylideneamino)triethylenetetramine have been synthesized and characterized by elemental and spectral analyses as well as x‐ray crystal diffraction. The FAB and TOF (time‐of‐flight) mass spectra reveal that the ligand acts as a heptadentate and that the metal versus ligand stoichiometry is 2:2. The structure of the lanthanum(III) complex has been determined by x‐ray single crystal diffraction. The lanthanum(III) ion is coordinated through the four nitrogen and the four oxygen atoms of the two ligands to form an eight‐coordinate configuration. The two lanthanum(III) ions are bridged by the two phenolate oxygen atoms in the complex. The structure is similar to that of the ligand containing p‐bromo substituents. The proton NMR spectra also show that the lanthanum(III) complex is a dimer.

Low‐Temperature Heat Capacity and Thermal Decomposition of Crystalline [Ho(Thr)(H2O)5] Cl3

Rare earth elements have been widely used in many areas. Rare earth complex bearing an amino acid was synthesized to study the influence and the long-term effect of rare earth elements on environment and human beings, because amino acid is the basic unit of the living things. Previous work on these kinds of complex is focused on synthesis and characterization of them. But their thermodynamic data have seldom been reported. Here we present the thermodynamic study of [ Ho (Thr) (H2O)(5)] Cl-3. The heat capacity of Holmium complex with threonine, [ Ho (Thr) ((HO)-O-2)(5)] Cl-3, was measured with an automatic adiabatic calorimeter in the temperature range from 79 K to 330 K and no thermal anomaly was found in this range. Thermodynamic functions relative to standard state 298.15 K were derived from the heat capacity data. Thermal decomposition behavior of the complex in nitrogen atmosphere in the range from 300 K to 900 K was studied by thermogravimetric (TG) technique and a possible decomposition mechanism was proposed according to the TG-DTG results.

Synthesis and Characterization of an Eight-Coordinated [Ho(hfa)₂(triglyme)][Ho(hfa)₄] Holmium Complex

Synthesis and Characterization of an Eight-Coordinated [Ho(hfa)₂(triglyme)][Ho(hfa)₄] Holmium Complex

Europium(III), Holmium(III), and Lutecium(III) Complexes with Octaphenyltetraazaporphyrin: State and Stability in Proton-Donor Media

Acid–base interaction of holmium(III) and lutecium(III) complexes with octaphenyltetraazaporphyrin in AcOH and AcOH–benzene and AcOH–H2SO4 systems was found to involve one nitrogen meso-atom. Stability constants of the obtained acid forms are determined. Solvoprotolytic dissociation of complexes in the systems based on AcOH is studied and its mechanism is discussed.

Influence of neutron irradiation on holmium acetylacetonate loaded poly(l-lactic acid) microspheres

Holmium-loaded microspheres are useful systems in radio-embolization therapy of liver metastases. For administration to a patient, the holmium-loaded microspheres have to be irradiated in a nuclear reactor to become radioactive. In this paper, the influence of neutron irradiation on poly(l-lactic acid) (PLLA) microspheres and films, with or without holmium acetylacetonate (HoAcAc), is investigated, in particular using differential scanning calorimetry (MDSC), scanning electron microscopy, gel permeation chromatography (GPC), infrared spectroscopy, and X-ray diffraction. After irradiation of the microspheres, only minor surface changes were seen using scanning electron microscopy, and the holmium complex remained immobilized in the polymer matrix as reflected by a relatively small release of this complex. GPC and MDSC measurements showed a decrease in molecular weight and crystallinity of the PLLA, respectively, which can be ascribed to radiation induced chain scission. Irradiation of the HoAcAc loaded PLLA matrices resulted in evaporation of the non-coordinated and one coordinated water molecule of the HoAcAc complex, as evidenced by MDSC and X-ray diffraction analysis. Infrared spectroscopy indicated that some degradation of the acetylacetonate anion occurred after irradiation. Although some radiation induced damage of both the PLLA matrix and the embedded HoAcAc-complex occurs, the microspheres retain their favourable properties (no/marginal release of Ho, preservation of the microsphere size), which make these systems interesting candidates for the treatment of tumours by radio-embolization.

Bidentate lactate binding in aqueous solution in a cationic, heptadentate lanthanide complex: an effective chiral derivatising agent.

The X-ray crystal structures of cationic, heptadentate lanthanide complexes of holmium and ytterbium bound to lactate are reported and the observed bidentate chelation in the solid state is consistent with near-IR CD (Yb) and solution NMR measurements; the complexes are shown to act as aqueous chiral derivatising agents for alpha-hydroxy acids.

Characterization of poly( l-lactic acid) microspheres loaded with holmium acetylacetonate

Holmium-loaded PLLA microspheres are useful systems in radioembolization therapy of liver metastases because of their low density, biodegradability and favourable radiation characteristics. Neutron activated Ho-loaded microspheres showed a surprisingly low release of the relatively small holmium complex. In this paper factors responsible for this behaviour are investigated, in particular by the use of differential scanning calorimetry, scanning electron microscopy, infrared spectroscopy and X-ray diffraction. The holmium complex is soluble in PLLA up to 8% in films and 17% in microspheres. Interactions between carbonyl groups of PLLA, and the Ho-ion in the HoAcAc complex, explain very satisfactorily the high stability of holmium-loaded microspheres.

The Complexes of Holmium with Methylenediphosphonate and 1-Hydroxyethylidenephosphonate

The composition and stability of holmium methylenediphosphonate (MDP) and 1-hydroxyethylidenephosphonate (HEDP) complexes were studied by potentiometric titration methods in 0.1M NaCl at 25 °C. It was found that besides L4− anions the protonated HnL(4−n)− species (n = 1–3 for MDP and n = 1–4 for HEDP) are present in the pH region 3 to 10. The presence of the undissociated acids (H4L) has not been unambiguously proved for MDP. The complexes of the composition HoHnL (n varies from 1 to −2 for MDP and from 1 to −1 for HEDP) have been found if the concentration of the ligand is higher than the concentration of holmium. The protonation constants of both acids and the stability constants of the complexes discussed were determined and the comparison with literature data of analogical complexes of other lanthanides was performed.

A holmium complex of a macrocyclic ligand (DOTA) and its isostructural europium analogue

The holmium and europium complexes of the tetraanion of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (H4DOTA), namely, sodium aqua(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetato)-holmium(III) tetrahydrate, Na[Ho(C 16 H 24 N 4 O 8 )(H 2 O)].4H 2 O, and sodium aqua(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetato)europium(III) tetrahydrate, Na[Eu(C 16 H 24 N 4 O 8 )(H 2 O)].4H 2 O, show nine-coordination around the metal ion, with a square antiprismatic coordination geometry involving four N- and four O-donor atoms of the DOTA ligand, and a coordinated water molecule in a capping position.

Characterization of structures and spectra of holmium complexes formed in the CO and N 2 matrices

The equilibrium geometry configurations and high-frequency IR spectra for the complexes HoL n (L = CO, N 2 , n = 1–6) are characterised by ab initio quantum-chemical calculations.

Determination of neodymium, holmium and erbium in mixed rare earths by norfloxacin

Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second derivative spectrum, Beer’s Law is obeyed from 5.0 × 10–5∼ 2.5 × 10–4 mol dm–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10–5 mol dm–3 of neodymium, 6.1 × 10–5 mol dm–3 of holmium and 6.0 × 10–5 mol dm–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth elements with good accuracy and selectivity, is described.