Luminescence and crystal field analysis of Eu in Eu[Co(CN)6]·4H2O

The vibrational spectra of Eu[Co(CN)₆]·4H₂O and luminescence spectra of Eu³⁺ in this compound, using 355 nm excitation at temperatures down to 10 K, have been assigned. A clear distinction is made between the n=5 and 4 members of the Ln[M(CN)₆]·nH₂O series from the vibrational spectra. The electronic spectra show prominent vibronic structures, particularly for the ⁵D₀→⁷F₂ sideband. A resonance occurs between the transitions ⁵D₀→⁷F₁(III) and ⁵D₀→⁷F₀+ν(Eu−N). A crystal field analysis of the derived energy data set is presented for Eu³⁺ in eight coordination geometry.     

Double-stranded helical lanthanide(III) supramolecular networks with rigid diimine ligands: Synthesis, structure, and physical properties

Two lanthanide coordination complexes [Nd(NO₃)₃(CH₃OH)₂(4,4′-bipy)₂] (1) (4,4′-bipy=4,4′-bipyridine) and [4,4′-Hbipy][La(NO₃)₄(H₂O)₂(4,4′-bipy)] (2), with a salt of cationic diprotonated 4,4′-bipy, [2(4,4′-H₂bipy)][4(NO₃)] (3), have been identified and isolated from a methanol solution of Ln(NO₃)₃·6H₂O, 4,4′-bipyridine and pyrazine in 1:2:1 ratio. Their structures have been determined by single-crystal X-ray diffraction analyses, which reveal that 1 has an interesting three-dimensional supramolecular architecture containing 2₁ double-stranded helical chains through hydrogen bonding and π–π interactions, while 2 and 3 have well defined infinite chiral 3D open networks that undergo self-interpenetration. The electrospray ionization mass spectra (ESI-MS) indicate that the covalent complex has higher stability than the electrostatic bonding one. ESI-MS/MS of these ions reveal that the Ln–O bond forms a stronger coordinated bonding than that of Ln–N system and the nitrate anion remains bound to the lanthanide centers after complete dissociation in methanol solution.     

Synthesis,structures and near-infrared luminescence properties of Ho and Yb coordination complexes

Four Ln³⁺ coordination complexes with the formulas [Ln(p-toluylate)₂(Ac)(H₂O)]_n (Ln=Ho 1, Yb 2) and {[Ln₂(OOCCH₂CH₂COO)₃(H₂O)₄]·6H₂O}_n (Ln=Ho 3, Yb 4) were synthesized hydrothermally. Their structures were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are isomorphic and form infinite 2D network structures comprising p-toluylate and acetate (Ac^–) moieties. Complexes 3 and 4 are also isomorphic and possess infinite 2D structures in which succinate acts as bridging ligands that are connected to a 3D hydrogen bonding network by O–H…O hydrogen bonds. Solid-state IR and UV-Vis-NIR spectra, excitation and emission spectra were determined for the four complexes at room temperature. Complexes 1 and 2 exhibit characteristic NIR emission bands of Ln³⁺ ions but these are shifted and split relative to the theoretical positions. This is also evident for their UV-Vis-NIR spectra. The influence of ligands on enhancing the NIR luminescence of Ln³⁺ ions in complexes is discussed.     

Structural, optical and scintillation properties of cerium cyclotriphosphates and polyphosphates

The cerium cyclotriphosphate CeP₃O₉·3H₂O and polyphosphate Ce(PO₃)₃ have been optically investigated for the first time. In both materials, excitation and emission spectra under UV and X-ray excitations as well as emission decays of Ce³⁺ were measured at room temperature. The spectroscopic results of anhydrous Ce(PO₃)₃, prepared by progressively heating the corresponding CeP₃O₉. 3H₂O, are discussed and correlated with the structural data.For the Ce(PO₃)₃ polyphosphate material, the Stokes shift of the d-f emission is very small (760 cm⁻¹), inducing an efficient ultraviolet luminescence and a new application as scintillator.     

Syntheses of two new hybrid metal-organic polymers using flexible aliphatic dicarboxylates and pyrazine: Crystal structures and magnetic studies

The reaction of metal ions, flexible aliphatic dicarboxylates and pyrazine in aqueous solution afford two new metal-organic coordination polymers, {[Cu₂(μ₂-η²-O₂C(CH₂)₂CO₂-η²-μ₂)₂(H₂O)₂]·2H₂O}_n (1) and [Eu₂(μ₂-η²-O₂CCH₂CO₂-η¹-μ₁)₂(μ₂-η²-O₂CCH₂CO₂-η²-μ₂)(H₂O)₆]_n (2). Polymer 1 contains the paddle-wheel cage dicopper(II) units, forming a one-dimensional (1D) double-stranded chain structure along the a-axis, in which the copper(II) atoms are bridged by the carboxylate groups of four succinates. The intradimer Cu-Cu distance is 2.613(2) Å; the interdimer Cu?Cu distance is 6.473 Å. To our knowledge, compound 1 represents the first example of a double-stranded chain structure containing dinuclear paddle-wheel type cage. In the three-dimensional (3D) compound 2, each central Eu(III) ion have a distorted monocapped square antiprism coordination geometry. The structure is built up from two types of polymeric chains with [EuO₆(H₂O)₃]_n units as tethers, resulting in microporous framework. The magnetic behavior of 1 shows that the occurrence of a strong antiferromagnetic coupling between the copper(II) ions through the short bridges via the carboxyl groups can be obtained; the best fittings to the experimental magnetic susceptibilities gave −2J=314 cm⁻¹.     

Structural characterisation of [Cu2(bptd) (H2O) Cl4] and [Ni2(bptd)2(H2O)4] Cl4·3H2O; evidence of null intramolecular exchanges by EPR and magnetic measurements

Using the 2,5-bis(2-pyridyl)-1,3,4-thiadiazole (bptd), we recently prepared [Cu₂(bptd) (H₂O) Cl₄] and [Ni₂(bptd)₂ (H₂O)₄] Cl₄, 3H₂O in which the magnetic centres are connected through one diazine+one chloro and two diazine ligand bridges, respectively. These two compounds are the first examples that show null intramolecular magnetic interactions despite M-M distances close to 3.7 Å within perfectly planar edifices:Down to , [Cu₂(bptd)Cl₄(H₂O)] is paramagnetic while, below T_t, half of the Cu²⁺ions interact, leading to residual paramagnetism of one Cu²⁺/f.u. Magnetic susceptibility measurements, EPR and pulsed EPR study indicate the original intermolecular nature of AF exchanges.[Ni₂(bptd)₂(H₂O)₄]Cl₄·3H₂O susceptibility obeys a Curie-law involving pure paramagnetism. Moreover, its EPR spectrum can be interpreted on the basis of virtual S=1 monomers. Below 70 K, Zero Field Splitting (D∼275 G) due to dipolar interactions without magnetic exchanges could be responsible for the LT spectra splitting. For both compounds, the thia role is suggested as partially responsible for the null-in-plane magnetic exchanges.     

Syntheses, structures, fluorescence and thermal properties of three lanthanide coordination polymers built by N-benzoyl-N′-(4-benzoxy)thiourea

Three novel lanthanide 1-D chain coordination polymers, namely {[Tb(μ₂-L)₂(η²-NO₃)(CH₃OH)(H₂O)]·0.5CH₃OH·0.5H₂O}_n (1), {[Dy(μ₂-L)₂(η²-NO₃)(CH₃OH)(H₂O)]·H₂O}_n (2) and {[Ce(μ₂-L)₂(η²-NO₃)(H₂O)₃]·H₂O}_n (3) (HL=N-benzoyl-N′-(4-benzoxy)thiourea), have been prepared and characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. The luminescence properties and themostabilities of polymers 1-3 have been determined as well.     

Synthesis, crystal structure, Cu doped EPR, thermal and voltammetric studies of [Ni(isonicotinamide)2(H2O)4]·(sac)2 single crystal

The single crystal of [Ni(ina)₂(H₂O)₄]·(sac)₂, (NINS), (ina is isonicotinamide and sac is saccharinate) complex has been prepared and its structural, spectroscopic and thermal properties have been determined. The title complex crystallizes in monoclinic system with space group P2₁/c, Z=2. The octahedral Ni(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate ina ligands through the ring nitrogen and four aqua ligands to form discrete [Ni(ina)₂(H₂O)₄] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bands. The magnetic environment of copper(II) doped NINS crystal has also been identified by electron paramagnetic resonance (EPR) technique. The g and A values of Cu²⁺ doped NINS single crystal were calculated from the EPR spectra recorded in three mutually perpendicular planes. These values indicated that the paramagnetic centre has a rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The complex exhibits only metal centred electroactivity in the potential range of −2.00, 1.25 V versus Ag/AgCl reference electrode.     

Crystal structure of Ni(II) complex and fluorescence properties of Zn(II) complex with the Schiff base derived from diethenetriamine and PMBP

The Schiff base, H₂L, was derived from 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and diethenetriamine. The crystal structure of [NiL(C₂H₅OH)]·H₂O obtained from ethanol solution was determined by X-ray diffraction analysis. The coordination geometry of Ni(II) ion is a distorted octahedron with three oxygen atoms and three nitrogen atoms. Under the excitation of ultraviolet light, strong fluorescence of solid Zn(II) complex was observed. In addition, the fluorescence enhancement was obtained in the presence of Zn²⁺ in THF solution of the ligand, indicating that H₂L may be a potential fluorescent sensor for Zn²⁺.     

Synthesis, Crystal Structure and Luminescent Property of Complex [Tb0.1Gd0.9(TPTZ)(H2O)6]Cl3·3H2O

The complex [Tb_0.1Gd_0.9(TPTZ)(H₂O)₆]Cl₃·3H₂O was prepared through the reaction of 2,4,6-tris-(2-pyridyl)-1,3,5-triazine (TPTZ) with TbCl₃:GdCl₃ (0.1:0.9) in absolute ethanol at room temperature. Single crystal X-ray diffraction revealed that the metal atom is nine-coordinated with three nitrogen atoms from one TPTZ ligand and six oxygen atoms from six water molecules. The complex emits intense green fluorescence under ultraviolet light. The luminescence peaks correspond to the characteristic emission ⁵D₄→⁷F_J (J = 3–6) transitions of the Tb³⁺ ion.     

Synthesis, crystal structure, Cu doped EPR and voltammetric studies of bis[N-(2-hydroxyethyl)ethylenediamine]zinc(II) squarate monohydrate

Crystal structure of [Zn(hydet-en)₂]·C₄O₄·H₂O (ZHES) (hydet-en is N-(2-hydroxyethyl)ethylenediamine) complex has been synthesized and characterized by analytical, spectroscopic (IR, UV/Vis) and voltammetric techniques. After doping Cu²⁺ ion, its magnetic environment has been identified by electron paramagnetic resonance (EPR) technique. The title complex crystalizes in monoclinic system with space group P2₁/c and with Z=4. Each hydet-en ligand acts as a tridentate ligand through the two N atoms and the hydroxyl O atom, resulting in a six coordinate Zn(II) ion. The EPR spectra were recorded in three perpendicular planes of Cu²⁺ doped ZHES single crystal. The calculated g and A values indicated that the paramagnetic center is rhombic symmetry with the Cu²⁺ ion having distorted octahedral environment. The molecular orbital bond coefficients of the Cu(II) ion in d⁹ state is also calculated by using EPR and optical absorption parameters. The dianion SQ²⁻ is oxidized reversibly in two consecutive steps to the corresponding radical monoanion and neutral form.     

On the spectra luminescence properties of charoite silicate

Charoite is a hydrous alkali calcium silicate mineral [K₄NaCa₇Ba_0.75Mn_0.2Fe_0.05(Si₆O₁₅)₂(Si₂O₇)Si₄O₉(OH)·3(H₂O)] exhibiting an intense lilac colour related to Mn²⁺ and Fe³⁺ colour centres. These ions also contribute to a strong luminescence at ∼585 and 705 nm. This work studies the thermal dependence of these luminescent centres by (i) thermoluminescence (TL) of pre-heated and pre-irradiated charoite aliquots, (ii) by time-resolved cathodoluminescence (TRS-CL) at room and cryogenic temperatures (RT and CT), (iii) by spatially resolved spectra CL under scanning electron microscopy (SRS-CL-SEM) and (iv) by ion beam spectra luminescence (IBL) with H⁺, H₂⁺ and ⁴He⁺ ions at RT and LT. The main peak, ∼585 nm, is linked to a transition ⁴T_1,2 (G)→⁶A₇(S) in Mn²⁺ ions in distorted six-fold coordination and the emission at ∼705 nm with Fe²⁺→Fe³⁺ oxidation in Si⁴⁺ lattice sites. Less intense UV-blue emissions at 340 and 390 nm show multi-order kinetic TL glow curves involving continuous processes of electron trapping and de-trapping along with an irreversible phase transition of charoite by de-hydroxylation and lattice shortening of Δa=0.219 Å, Δb=0.182 Å; Δc=0.739 Å. The Si-O stressed lattice of charoite has non-bridging oxygen or silicon vacancy-hole centres, and Si-O bonding defects which seem to be responsible for the 340 nm emission. Extrinsic defects such as the alkali (or hydrogen)—compensated [AlO₄/M⁺] centres could be linked with the 390 nm emission. Large variations in 585 and 705 nm intensities are strongly temperature dependent, modifying local Fe-O and Mn-O bond distances, short-range-order luminescence centres being very resistant under the action of the heavy ion beam of ⁴He⁺. The SRS-CL demonstrates strong spatial heterogeneity in the luminescence of the charoite.     

Mixed valence states in cobalt iron cyanide

Cobalt iron cyanide with both Co and Fe in mixed valence states were prepared and characterized. In this mixed valence system the cobalt atom is found both as high spin Co(2+) and low spin Co(III) while iron always appears in low spin state to form two solid solutions: Co(2+)Co(III) hexacyanoferrates (II,III), and Co(2+)Co(III) hexacyanoferrate (II). Such solid solutions have the following formula units: (Co²⁺)_x(Co^III)_1−xK[(Fe^II)_1−x(Fe^III)_x(CN)₆]·H₂O and (Co²⁺)_1.5x(Co^III)_1−xK[Fe^II(CN)₆]·yH₂O (0?x?1, 1?y?14). Compounds within these two series were characterized from Infrared, Mössbauer, X-ray diffraction and thermo-gravimetric data, and magnetic measurements at low temperature. A model for their crystal structure is proposed and the structure for a representative composition refined from XRD powder patterns using the Rietveld method. A simple and reproducible procedure to prepare these solid solutions is provided. Within hexacyanoferrates, such mixed valence states system in both metal centres shows unique features, which are discussed from the obtained data.     

Structural characterization of nanocrystalline CrOOH·2H2O aerogel by X-ray diffraction

The nanostructured powder prepared by critical CO₂ extraction of the urea-assisted wet chromia gel mixture at 373 K in vacuum was studied by X-ray diffraction techniques. Thermoanalytical methods showed the presence of the lattice water molecules in the resulting phase corresponding to a chemical formula CrOOH·2H₂O. The CrOOH·2H₂O nanocrystals of 3-5 nm in diameter were observed in transmission electron microscopy and their structure was derived from the Rietveld analysis in which the disorder contribution to the X-ray scattering was implemented. The structural model shows that the hexagonal unit cell of α-CrOOH undergoes monoclinic distortion with half of the O⁻² anions and OH⁻ groups being replaced by bonded water molecules in the three-dimensional packing resulting in half of the sites in regular Cr⁺³ octahedra being vacant. Further examination of the quasi-crystalline disordered state of the CrOOH·2(H₂O) nanocrystals was performed by model independent method of Radial Distribution Function (RDF). This complementary technique is sensitive to the molecular composition and allows to assess the average atomic (or electron) density distribution and the spacings of the atomic arrangements in the nearest neighbor shells comprising the range of the crystalline order in the structure of this material.     

A new isomorph of ferrous chloride tetrahydrate: A Fe Mössbauer and X-ray crystallography study

This paper outlines the discovery of a newly characterised isomorph of ferrous chloride tetrahydrate, Fe(H₂O)₆·FeCl₄(H₂O)₂, which was initially identified by X-ray crystallography and confirmed by Mössbauer spectroscopy. The X-ray analysis identified the space group as P2₁/c with essentially the same unit cell dimensions as the well-known isomorph, FeCl₂·4H₂O, except that one edge is doubled due to two discrete [Fe(H₂O)₆]²⁺ and [FeCl₄(H₂O)₂]²⁻ species per unit cell. Time-series Mössbauer studies revealed this new isomorph to be unstable upon atmospheric exposure, decaying to the well-known structure over a period of days. Density functional theory calculations support an energetically favourable catalytic interconversion involving adsorbed water. A high-precision redetermination on the FeCl₂·4H₂O crystal structure, which is also in space group P2₁/c, is also reported, providing the unit cell parameters: a=5.8765(3) Å, b=7.1100(3) Å, c=8.4892(5) Å and β=111.096(1)°.     

Synthesis of basic magnesium carbonate microrods with a “house of cards” surface structure using rod-like particle template

Basic magnesium carbonate (Mg₅(CO₃)₄(OH)₂·4H₂O) microrods with a surface structure of “house of cards” have been synthesized without any alkaline reagent, using rod-like particles, magnesium carbonate trihydrate, as templates. The product was characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The transformation process from rod-like MgCO₃·3H₂O particles to Mg₅(CO₃)₄(OH)₂·4H₂O microrods with a surface structure of “house of cards” was recorded. Preliminary discussions on possible growth mechanisms of Mg₅(CO₃)₄(OH)₂·4H₂O microrods are also proposed in this paper.     

Comparative study of crystal field effects for Ni ion in LiGa5O8, MgF2 and AgCl crystals

Exchange charge model (ECM) of crystal field was used to calculate the crystal field parameters (CFPs) and model the energy levels for Ni²⁺ ion in LiGa₅O₈, MgF₂ and AgCl crystals. Calculated energy levels (including splitting of the orbital triplets) are in good agreement with experimental absorption spectra. Covalent effects were shown to play an important role in all considered crystals. Bilinear forms built up from the overlap integrals between (Ni²⁺-Cl⁻)→(Ni²⁺-O²⁻)→(Ni²⁺-F⁻) pairs were considered a quantitative measure of the covalent (nephelauxetic) effects.     

A luminescent dinuclear Eu(III) complex based on 2,8-bis(4′,4′,4′,-trifluoro-1′,3′-dioxobutyl)-dibenzothiophene for light-emitting diodes

A dinuclear Eu (III) complex Eu₂(dbt)₃·4H₂O was synthesized, where H₂dbt was 2,8-bis(4′,4′,4′,-trifluoro-1′,3′-dioxobutyl)-dibenzothiophene. The complex emits the characteristic red luminescence of Eu³⁺ ion due to the ⁵D₀→⁷F_J(J=0-4) transitions under 395 nm-light excitation with a luminescent quantum efficiency of 17%. The complex is thermally stable up to 280 °C. It was found that the complex can be effectively excited by a 395 nm-emitting InGaN chip. Bright red light was obtained using the complex as light color-conversion material.     

Influence of the Ga addition on optical properties of Pr in Ge–Sb–Se glasses

Absorption and emission spectra for the ³H₄↔(³F₂, ³H₆) transition of Pr³⁺ ions embedded in Ge–Sb–Se glasses turned out to change systematically upon the introduction of a small amout of Ga. Clear blueshift of the absorption peak wavelengths together with the decrease of absorption cross-section was evident in these glasses containing Ga. We believe that the Ga addition into the conventional covalent selenide glasses makes chemical bonds between rare earth atoms and Se atoms more ionic due to preferential location of the GaSe₄ tetrahedra at the second coordination shell of a rare earth atom. Taking into consideration the hypersensitive nature of the Pr³⁺: ³H₄↔³F₂ transition, the observed blueshift may manifest the enhanced ionicity of the chemical bonds between Pr and Se in the current Ga-containing glasses.     

Cr-related centers in Gd3Ga5O12 polycrystals

The luminescence excitation spectra, emission spectra under photo- and X-ray excitation, luminescence decay kinetics and thermostimulated luminescence (TSL) of Gd₃Ga₅O₁₂ garnet (GGG) polycrystalline samples have been investigated. It was established that the spectrum of Cr³⁺ ion emission were present in all TSL peaks. The activation energies of traps that are responsible for appearance of TSL in the region 295-600 K were estimated. It is shown that delocalization of electrons from the Cr³⁺e traps leads to the appearance of thermoluminescence (TL) glow peak at 390 K. The nature of other TSL peaks is discussed. The influence of visible light on the TSL intensity of the preliminary X-ray-irradiated samples is shown.