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Crystallographic investigations of eight homoleptic N,N′-dimethylpropyleneurea (dmpu) coordinated metal ions in the solid state, [Mg(dmpu)5]I2 (1), [Ca(dmpu)6]I2 (2), [Ca(dmpu)6](ClO4)2 (3), [Ca(dmpu)6](CF3SO3)2 (4), [Sr(dmpu)6](CF3SO3)2 (5), [Ba(dmpu)6](CF3SO3)2 (6), [Sc(dmpu)6]I3 (7), and [Pr(dmpu)6]I(I3)2 (8), and the complex [CoBr2(dmpu)2] (9) as well as the structures of the dmpu coordinated calcium, strontium, barium, scandium(III) and cobalt(II) ions and the cobalt(II) bromide complex in dmpu solution as determined by EXAFS are reported. The methyl groups in the dmpu molecule are close to the oxygen donor atom, causing steric restrictions, and making dmpu space-demanding at coordination to metal ions. The large volume required by the dmpu ligand at coordination contributes to crowdedness around the metal ion with often lower coordination numbers than for oxygen donor ligands without such steric restrictions. The crowdedness is seen in M⋯H distances equal to or close to the sum of the van der Waals radii. To counteract the space-demand at coordination, the dmpu molecule has an unusual ability to increase the M–O–C bond angle to facilitate as large coordination numbers as possible. M–O–C bond angles in the range of 125–170° are reported depending on the crowdedness caused by the coordination figure and the M–O bond distance. All reported structures of dmpu coordinated metal ions in both the solid state and dmpu solution are summarized to study the relationship between the M–O–C bond angle and the crowdedness around the metal ion. However, highly symmetric complexes seem to be favoured in the solid state due to favourable lattice energies. As a result, the dmpu coordinated lanthanoid(III) ions are octahedral in the solid state, while they, except lutetium, are seven-coordinate in the dmpu solution. [ABSTRACT FROM AUTHOR]

Strontium isotope composition is a powerful proxy for tracking the source and evolution of a range of geological processes in magmatic, sedimentary and metamorphic environments. Owing to the mobility of Sr with fluids, Sr isotope is also an ideal proxy to investigate, and has been extensively used to tackle the history of magmatic–hydrothermal systems and associated water–rock interactions. Apatite is an excellent choice for such a purpose as it is ubiquitous in almost all these environments, and contains abundant Sr but exceptionally limited Rb. Microanalytical techniques are preferred for apatite Sr isotope studies since most apatites are small in size and may have a complicated growth history to be decoded. Matrix-matched reference materials are a prerequisite for microanalysis, and although variable F- and OH-rich apatite Sr isotope reference materials have been developed, chlorine-rich ones are lacking. Here, we further evaluate Eppawala-AP, a Cl-rich apatite, as a potential Sr isotope reference material. Our extensive Sr isotope microanalysis at three laboratories confirmed that the Eppawala-AP was homogeneous in terms of Sr isotope composition, with a recommended 87Sr/86Sr ratio of 0.704989 ± 0.000017 (2 SD, n = 9) determined by thermal ionization mass spectrometry from another two laboratories. The Eppawala-AP also had homogeneous trace element contents and Nd isotope composition. Therefore, Eppawala-AP can be used as a Sr isotope reference material, and also as a working reference to monitor the Nd isotope and trace element analysis, and thus could be expected to fill the much-needed gap for Cl-rich apatite reference materials and facilitate more precise and accurate analysis. [ABSTRACT FROM AUTHOR]

In this work, a sustainable one-pot precipitation method was applied for synthesizing strontium phosphate nanoparticles (SrPO NPs), which can be utilized as effective charge separation photocatalysts for the degradation of oncogenic naphthylamine derivatives (congo red). Significant photocatalytic activity of SrPO NPs corresponding to the lowest optical band gap energy of 2.19 eV was calculated by the Tauc plot. The synthesized SrPO NPs belong to the orthorhombic Pnam E crystalline system in which phosphate groups are linked to strontium ions with an average size of 14 nm. The uniform formation of nanoflake-like morphology was analyzed by FE-SEM and HR-TEM techniques. Enhanced photodegradation owing to superior charge separation and interfacial charge transport resistance was confirmed by EIS analysis. The SrPO NPs photocatalyst achieved 98% degradation efficiency under visible light within a short span of time under optimal conditions. The rate constant K = 0.0892 × 10−1 evidently proved that the photodegradation of CR obeys pseudo-first-order reaction kinetics. ROS involved in photodegradation, analyzed by various radical scavengers confirm the involvement of hydroxyl and superoxide radicals during degradation. Finally, the reusability after five consecutive measurements demonstrates that SrPO NPs are excellent and suitable photocatalysts for the detoxification of the anionic azo derivative congo red. [ABSTRACT FROM AUTHOR]

New coordination polymers with 2D network structures with fluorine directly coordinated to the metal ion were prepared both via mechanochemical synthesis and fluorolytic sol–gel synthesis. Depending on the synthesis route, the samples show different particle sizes, according to SEM imaging. The crystal structures of barium acetate fluoride, strontium acetate fluoride, and lead acetate fluoride (BaF(CH3COO), SrF(CH3COO) and PbF(CH3COO)) were solved from X-ray powder diffraction data. The structure solution is backed by the results from 19 F MAS NMR, FT IR data, and thermal analysis. The calculated chemical shifts of the 19 F MAS NMR spectra coincide well with the measured ones. It turns out that the grinding conditions have a remarkable influence on the mechanochemical synthesis and its products. Our systematic study also indicates a strong influence of the atomic radii of Ca, Sr, Ba, and Pb on the success of the syntheses. [ABSTRACT FROM AUTHOR]

Using ethylenediaminetetraacetic acid (EDTA) as a chelating agent and urea as a directional template, we report an effective method for the synthesis of porous strontium hydroxyapatite (SrHAp) microspheres employing homogeneous precipitation. More importantly, we can easily control the pore size (d) of porous SrHAp microspheres through the elaborate choice of reaction temperature (T) at atmospheric pressure. The experimental results show that the d of porous SrHAp microspheres rises gradually with the increase of T. In addition, with the increase of reaction time at the same T, the d of the microspheres remained unchanged, but the diameter of porous SrHAp microspheres gradually increased, and remained unchanged after 36 h. According to the Laplace equation, Kelvin equation and Clapeyron equation, the relationship of d and T is deduced as follows:. The experimental data (T, d) agreed with it. In particular, based on the unique role of EDTA and CO2 bubbles (urea hydrolysis) in the preparation of porous SrHAp microspheres, the self-assembly pore-forming mechanism of foam boundary templates was proposed. First, urea was hydrolyzed to produce CO2 bubbles (foam boundary template) and OH−, and EDTASr (EDTA chelates strontium ions) and H3O+ (acidic system) formed a liquid film-chelating ion electronic double layer (LFCIEDL) on the surface of CO2 bubbles, which not only chelated and located Sr2+, but also formed a stable foam boundary template. Secondly, Sr2+, H2PO4− and OH− were homogeneously nucleated in the Plateau borders among the bubbles. After that, along the bubble liquid film surface, Sr2+ is orientationally released from the outer edge to the inner. SrHAp lamellae were formed by self-assembly method, then they were interconnected. In addition, OH− produced by urea hydrolysis continuously provides power for self-assembly oriented growth. Finally OH− completely destroys the LFCIEDL on the surface of the bubble, causing the bubble to break, and the porous SrHAp microspheres are formed. [ABSTRACT FROM AUTHOR]

Recently, aminohydroximate ligands have found wide applications in the fascinating class of polynuclear metallamacrocyclic compounds named 15-MC-5 metallacrowns. The enhanced interest in water-soluble aminohydroximate Ln(iii)–Cu(ii) complexes is largely due to their rich coordination chemistry, diverse properties and ease of synthesis. We examined glycinehydroxamic acid as a simple ligand for the preparation of the first water-soluble polynuclear metallamacrocyclic Sr(ii)–Cu(ii) compound. The complex Sr(H2O)3[15-MCCuGlyha-5](Cl)2 was synthesized and characterized structurally and spectroscopically. The single-crystal structure reveals the classic metallamacrocyclic 15-MC-5 configuration. The Sr(ii) ion is located at the center of the 15-MCCu(II)Glyha-5 ring and coordinated by five oxygen atoms of the cycle in the equatorial plane and an additional three oxygen atoms of the water molecules at apical positions. Detailed DFT and QT AIM studies were carried out for the hydrated isoelectronic Sr[15-MCCuGlyha-5]2+ and Y[15-MCCuGlyha-5]3+ systems. The ionic contribution to the metal–ligand interactions appears to be higher for the Sr(ii) derivative despite the smaller charge separation. DFT calculations suggest a thermodynamically favorable substitution of the Sr(ii) central ion with Y(iii). Indeed, it was shown experimentally that the strontium ion can be easily replaced by yttrium. Preliminary cytotoxic studies revealed the low toxicity of the strontium complex and its yttrium analogue, so the water-soluble Sr(ii) and Y(iii) metallacrowns can be further investigated as possible platforms for the development of new 90Sr and 90Y radiotherapy drugs. [ABSTRACT FROM AUTHOR]

Efficient and irreversible capture of radioactive nuclides is an important environmental protection task when disposing of nuclear wastewater. This paper uses an “ion trapping” concept to design an efficient adsorbent based on a metal–organic framework (MOF), for removal of radioactive strontium from nuclear wastewater. Two functionalized MOFs were achieved by the introduction of sulfate or oxalate into the pore structure of MOF-808, giving MOF-808-SO4 and MOF-808-C2O4, respectively. These functionalized MOF-808 materials exhibit excellent ability to remove Sr2+ from acidic solution due to their particular trapping action, with the maximum Sr2+ adsorption capacities of 176.56 mg g−1 and 206.34 mg g−1 for MOF-808-SO4 and MOF-808-C2O4, respectively, surpassing most other inorganic materials. Additionally, 99% of Sr2+ is removed by MOF-808-SO4 and MOF-808-C2O4 after reaching the equilibrium. Remarkably, these two functionalized MOF-808 materials exhibited selectivity for the removal of Sr2+ from simulated mixed nuclear wastewater, even when there are 10 times as many co-existing ions as Sr2+ ions, demonstrating that anchoring of the trapping groups is a good way to improve Sr2+ adsorption capacity on MOFs. Moreover, both functionalized MOF-808 materials trap Sr2+ ions irreversibly, suggesting these trapping groups have strong ability to bind with Sr2+. A mechanism study indicated no proton ion exchange occurred during the adsorption process, so the functionalized groups anchored to MOFs play an important role in Sr2+ adsorption. Our present study provides an efficient way to design new adsorbents for the removal of radioactive strontium and other radionuclides from nuclear wastewater. [ABSTRACT FROM AUTHOR]

Three heterobimetallic complexes of formula [Ca2Cu3(mpyba)2(2-apyma)(H2O)7]·8.3H2O (1), [Sr2Cu3(mpyba)2(2-apyma)(H2O)8]·11.6H2O (2) and [Sr4.5Cu4(mpyba)4(ox)(H2O)20]·8.5H2O (3) [H4mpyba = N,N′-2,6-pyridinebis(oxamic acid), 2-apyma = 2-(6-aminopyridinyl)oxamate and ox = oxalate] have been synthesized and structurally characterized. Complexes 1 and 2 are isostructural compounds, with tricopper(ii) units having mpyba and its hydrolytic product (2-apyma) as ligands. They are interlinked through strontium(ii) (1) and calcium(ii) (2) ions to afford neutral two-dimensional networks. Two of the copper(ii) ions are five-coordinate in distorted square pyramidal (Cu3) and trigonal bipyramidal (Cu1) surroundings, whereas the other (Cu2) is six-coordinate in an elongated octahedral environment. The main difference between their structures, apart from the number of water molecules, resides in the nature of the alkaline earth cation coordinated to the oxamate fragments, Sr2+ (1)/Ca2+ (2), which exhibit eight and seven coordination, respectively. The π–π interactions and an extensive network of hydrogen bonds in 1 and 2 lead to supramolecular 3D structures. The relatively small size of their cavities, in the micropore domain, hinders the inclusion of N2 but allows CO2 adsorption (0.45 and 0.52 mmol g−1 for 1 and 2, respectively). The structure of 3 is made up of [3,3] metallacyclophane-type motifs, having the formula [Cu2(mpyba)2(H2O)2]4−. These act as tetrakis(bidentate) ligands towards the strontium(ii) ions (Sr1, Sr2 and Sr3), leading to a sheet-like polymer growing in the bc plane, which extends further along the crystallographic a axis by a bis(chelating) oxalate between the Sr1 atoms. The investigation of the magnetic properties of 1–3 in the temperature range 1.9–300 K shows the occurrence of an overall antiferromagnetic behaviour for 1 and 2 [J12 = J23 = −9.71(2) (1) and −10.81(5) cm−1 (2), with the Hamiltonian being defined as H = −J12S1·S2−J23S2·S3 + gβH[S1 + S2 + S3], and a ferromagnetic coupling within the dicopper(ii) metallacylophane unit of 3 [J = +1.86(1) cm−1 through the Hamiltonian H = −JS1·S2 + gβH(S1 + S2)]. Simple orbital symmetry considerations (1–3) and the spin polarization mechanism (3) account for the observed magnetic properties. [ABSTRACT FROM AUTHOR]

This article presents the investigation of the coordination behavior of a newly synthesized tricarboxylate ligand, obtained by joining imidazole dicarboxylic acid and 4-carboxybenzyl moieties [cbimdaH3, 1-(4-carboxybenzyl)-1H-imidazole-4,5-dicarboxylic acid]. Two novel coordination polymers were obtained through solvothermal reactions under similar conditions namely [Sr(cbimdaH)(H2O)]n (1) and [Cd2(cbimdaH)2(H2O)6]n·(DMF)3n(H2O)3n (2), with the ligand behaving as a dianionic tricarboxylate linker. The single crystal X-ray structures show that while 1 forms a 3D coordination polymer, 2 forms a 1D polymer which is further assembled in three dimensions through supramolecular interactions (H-bonding). Complex 1 consists of Sr2+ ions in a distorted dodecahedral coordination geometry, while 2 consists of Cd2+ ions in distorted pentagonal bipyramidal geometries. A topology study reveals that 1 has a new topology based on the 5,6-coordinated 3D net architecture. The luminescence properties of the complexes in the solid state and their thermal stabilities were studied. [ABSTRACT FROM AUTHOR]

A novel heterometallic MnSr complex containing the Mn3SrO4 cuboidal moiety and all types of µ-O2--moieties observed in the oxygen-evolving complex (OEC) in Sr2+-containing photosystem II (PSII) has been synthesized and characterized, which provides a new synthetic model of the OEC. [ABSTRACT FROM AUTHOR]