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A series of six novel salts of 5, 6-dichloro-2, 3- dicyanosemiquinone (DDQ) radical anions with aromatic cations is studied by structural characterization, magnetization, and conductivity measurements. Different types of stacking of DDQ radicals, which determine electrical and magnetic properties, are observed: regular stacks of equidistant radicals (resulting in semiconductivity along the direction of stacking), stacks of pancake-bonded dimers, isolated pancake- bonded dimers, and mixed stacks comprising DDQ radicals and aromatic cations. General features of pancake bonding of DDQ radicals are defined: parallel ring planes, offset along the carbonyl···carbonyl axis by 2.05–2.15 Å, and interplanar separations of 2.90–2.95 Å (for pancake-bonded dimers) or 3.08– 3.24 Å (for regular stacks of equidistant radicals).

Seven novel oxalate-based [CuIICrIII] compounds: [Cu4(terpy)4Cl5][Cr(C2O4)3]·9H2O (1 ; terpy = 2, 2’:6’, 2’’- terpyridine), {; ; [Cr2Cu4(H2O)2(terpy)4(C2O4)7]·10H2O}; ; n (2), [Cr2Cu4(H2O)2(terpy)4(C2O4)7]·12H2O (3), [Cu(H2O)3(terpy)][CrCu(H2O)(terpy)(C2O4)3]2·9H2O (4), [Cu(H2O)(terpy)(NO3)][CrCu(H2O)(terpy) (C2O4)3]·6H2O (5), [CrCu2(terpy)2(C2O4)3(NO3)]·1.5H2O·CH3OH (6) and [Cr2Cu4(H2O)4(terpy)4(C2O4)6] [Cr2Cu2(terpy)2(C2O4)6]·9H2O·CH3OH (7) were obtained from the reaction of an aqueous solution of the building block [Cr(C2O4)3]3− and a methanol solution containing Cu2+ ions and terpyridine ligand by the layering technique. Interestingly, changing only the anion of the starting salt of copper(II), NO3 − instead of Cl−, resulted in an unexpected modification in the bridge type, namely oxalate (compounds 2–7) versus chloride (compound 1). During the crystallization process in the test tube, the partial decomposition of the tris(oxalato)chromate(III) anion leads to the release of the oxalate ligand from the coordination sphere of chromium(III). Consequently, this oxalate ligand is coordinated to copper(II) ions in the reaction mixture, resulting in the oxalate-bridged cationic moieties of copper(II) ions [(terpy)Cu(μ-C2O4)Cu(terpy)]2+ of 2 and 3. Compounds 4–7 were formed in the same test tube using identical components as for 2 and 3, but in a different ratio ; during preparation, the starting material did not decompose and retained its original role as a building block. The compounds were studied by single-crystal X-ray diffraction, IR spectroscopy, magnetization measurements and density functional theory (DFT) calculations. Compound 1 exhibits a ground-state spin of 1 due to antiferromagnetic and ferromagnetic interactions of Cu2+ ions across the chloride bridges in the tetramer ; ferromagnetic coupling transferred through the oxalate bridge was found between Cu2+ ions in compound 2 and between Cu2+ and Cr3+ in compounds 4 and 5. Since compound 3 is considered to be a very similar fragment of compound 2, a ferromagnetic interaction between two Cu2+ ions bridged by a bis(bidentate) oxalate group is also expected. The performed calculations for compound 7 indicate that the main interaction is ferromagnetic.

Tetrachlorocuprate(II) hybrids of the three anisidine isomers (ortho-, meta-, and para-, or 2-, 3-, and 4-methoxyaniline, respectively) were prepared and studied in the solid state via X-ray diffraction and magnetization measurements. Depending on the position of the methoxy group of the organic cation, and subsequently, the overall cation geometry, a layered, defective layered, and the structure comprising discrete tetrachlorocuprate(II) units were obtained for the para-, meta-, and ortho-anisidinium hybrids, respectively. In the case of layered and defective layered structures, this affords quasi-2D-layered magnets, demonstrating a complex interplay of strong and weak magnetic interactions that lead to the long-range ferromagnetic (FM) order. In the case of the structure with discrete CuCl42– ions, a peculiar antiferromagnetic (AFM) behavior was revealed. The structural and electronic origins of magnetism are discussed in detail. To supplement it, the method for calculation of dimensionality of the inorganic framework as a function of interaction length was developed. The same was used to discriminate between n-dimensional and “almost” n-dimensional frameworks, to estimate the organic cation geometry limits for layered halometallates, and to provide additional reasoning behind the observed relation between cation geometry and framework dimensionality, as well as their relation to differences in magnetic behavior.

Seven novel oxalate-based [Cu

From the reaction of 2-hydroxy-6-methylpyridine (L) with iron(II) tetrafluoroborate, a new mononuclear iron(III) octahedral complex [FeL6](BF4)3 has been isolated. The color of the complex reversibly changed from red at room temperature to yellow-orange at the liquid nitrogen temperature. Magnetization measurements indicate that iron(III) in [FeL6](BF4)3 is in a high-spin state S = 5/2, from room temperature to 1.8 K. The high-spin ground state of iron(III) is also confirmed by DFT calculations. Although the spin-crossover of the complex is not observed, X-band and multifrequency high-field/high-frequency electron spin resonance (ESR) spectroscopy shows rather uncommon iron(III) spectra at room temperature and an unusual change with cooling. Spectral simulations reveal that the S = 5/2 ground state multiplet of the complex can be characterized by the temperature independent axial zero-field splitting parameter of |D| = +2 GHz (0.067 cm−1) while the value of the rhombic parameter E of the order of some tenths MHz increases on lowering the temperature. Single crystal X-ray diffraction (SCXRD) shows that the iron(III) coordination geometry does not change with temperature while supramolecular interactions are temperature dependent, influencing the iron(III) rhombicity. Additionally, the DFT calculations show temperature variation of the HOMO–LUMO gap, in agreement with the changes of color and ESR-spectra of the iron(III) complex with temperature.

Inorganic chemistry 61(45), 18181 - 18192 (2022). doi:10.1021/acs.inorgchem.2c02898, MOF-74 is an archetypal magnetic metal–organic framework (MOF) family, with metal nodes bridged by 2,5-dioxido-1,4-benzenedicarboxylic acid (H$_4$dobdc) and arranged into one of the simplest representations of the 1D Ising magnetic model. Recently, a novel mechano-synthetic approach opened a pathway toward a series of bimetallic multivariate (1:1) M1M2-MOF-74 materials, with the uniform distribution of metal cations in the oxometallic chains, offering a unique opportunity to investigate low-dimensional magnetism in these heterometallic MOFs. We explore here how different mechanochemical procedures affect the interaction between the metal nodes of the model system of three multivariate copper(II)/zinc(II)-MOF-74 materials, two of which were obtained through a template-controlled procedure, and the third one was obtained by recently developed mechanical MOF-alloying combined with subsequent accelerated aging. While the three Cu/Zn-MOF-74 products have almost identical powder X-ray diffraction (PXRD) diffractograms and Fourier transform infrared spectra, they differ significantly in their magnetic properties, as revealed through detailed magnetization and X-band and multifrequency high-field electron spin resonance measurements. The magnetic results of the three multivariate Cu/Zn-MOF-74s were compared to the properties of the monometallic Cu-MOF-74, which shows antiferromagnetic intrachain and weaker ferromagnetic interchain interactions. Energy-dispersive X-ray spectroscopy/scanning electron microscopy and solid-state nuclear magnetic resonance spectroscopy helped rationalize the observed differences in magnetization, and in situ synchrotron PXRD monitoring of template-controlled MOF formation revealed different reaction pathways when using the zinc or copper intermediates, involving even the fleeting occurrence of a rare MOF-74 polymorph., Published by American Chemical Society, Washington, DC

Yttrium manganite, YMnO3, was doped with different concentrations of titanium (x = 0, 0.04, 0.08, 0.10, 0.15, 0.20) in order to improve the microstructural and multiferroic properties. The powders were prepared using sol-gel polymerization complex method from citrate precursors. Depending on the titanium concentration, the hexagonal structure and/or the rhombohedral superstructure are present in the sintered samples. The YMn1–xTixO3+δ (x = 0.10, 0.15, 0.20) ceramic samples showed significantly reduced density of microcracks, and of inter- and intragranular pores, and relative densities greater than 90%. The structural parameters for YMn1–xTixO3+δ (x = 0, 0.10, 0.15) were correlated with the results of magnetic and ferroelectric measurements. The most of titanium-doped samples showed a reduction of the leakage current density in comparison with undoped YMnO3, and their ferroelectric responses were slightly improved. The modifications in structural arrangement resulted in partial suppression of ideal antiferromagnetic ordering visible through decrease of the Néel temperature and Weiss parameter, as well as the appearance of weak ferromagnetism and increase of magnetization (especially, in samples x = 0.08, 0.10, 0.15). These changes in physical quantities most likely originated from incorporation of the uncompensated magnetic moments and possible spin canting induced by enhanced symmetry break of the superexchange bridges.

International audience; The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of the corresponding CAs. However, this transition has thus far been studied in only two types of alloy systems: crystalline alloys of iron group metals (such as the Cantor alloy and its derivatives) and both amorphous (a-) and crystalline alloys, TE-TL, of early (TE = Ti, Zr, Nb, Hf) and late (TL = Co, Ni, Cu) transition metals. Here, we briefly overview the main results for the transition from HEAs to CAs in these alloy systems and then present new results for the electronic structure (ES), studied with photoemission spectroscopy and specific heat, atomic structure, thermal, magnetic and mechanical properties of a-TE-TL and Cantor-type alloys. A change in the properties of the alloys studied on crossing from the HEA to the CA concentration range mirrors that in the ES. The compositions of the alloys having the best properties depend on the alloy system and the property selected. This emphasizes the importance of knowing the ES for the design of new compositional complex alloys with the desired properties.

A novel one-dimensional (1D) oxalate-bridged coordination polymer of iron(III), {[NH(CH3)(C2H5)2][FeCl2(C2O4)]}n (1), exhibits remarkable humidity-sensing properties and very high proton conductivity at room temperature (2.70 × 10−4 (Ω·cm)−1 at 298 K under 93% relative humidity), in addition to the independent antiferromagnetic spin chains of iron(III) ions bridged by oxalate groups (J = −7.58(9) cm−1). Moreover, the time-dependent measurements show that 1 could maintain a stable proton conductivity for at least 12 h. Charge transport and magnetic properties were investigated by impedance spectroscopy and magnetization measurements, respectively. Compound 1 consists of infinite anionic zig-zag chains [FeCl2(C2O4)]nn− and interposed diethylmethylammonium cations (C2H5)2(CH3)NH+, which act as hydrogen bond donors toward carbonyl oxygen atoms. Extraordinarily, the studied coordination polymer exhibits two reversible phase transitions: from the high-temperature phase HT to the mid-temperature phase MT at T ~213 K and from the mid-temperature phase MT to the low-temperature phase LT at T ~120 K, as revealed by in situ powder and single-crystal X-ray diffraction. All three polymorphs show large linear thermal expansion coefficients.

Metal organic compound (C2H5NH3)2CuCl4 belongs to the family of layered perovskite multiferroic materials. It consists of ferromagnetic layers of corner sharing [CuCl4]2− octahedra connected by organic ions (two layers of [C2H5NH3]+). In this work we have studied magnetic properties of (C2H5NH3)2CuCl4 using SQUID magnetometer and AC susceptometer. Temperature dependence of magnetization showed existence of the antiferromagnetic transition at 10.2 K which changes to ferromagnetic with the application of moderate magnetic field. Near structural transition temperatures the anomaly of magnetization was observed. Hysteresis loops showed ferromagnetic behaviour for T T N and existence of anisotropy. Results of AC measurements showed no frequency dependence of the susceptibility and obtained temperature dependence of nonlinear susceptibility can be interpreted as a result of successive crossovers between different regimes.

The two red centrosymmetric Ni(II) tetrameric complexes with defective double-cubane core, [Ni2L2(H2O)]2·0.75 CH3OH (1) and [Ni2L2(CH3CN)]2 (2) (H2L = N-(2-hydroxy-5-methylphenyl)- salicylideneimine), have been isolated and magnetically characterized, emphasizing the effect of the reaction temperature on structural and magnetic properties of isolated complexes. Prevailing antiferromagnetic interactions in the complexes are observed leading to the non- magnetic ground state. Comparation with the known magneto-structural correlations in nickel cubane and dicubane complexes is discussed.

Pure and Co

The synthesis and the structural, spectroscopic, thermal, magnetic and electrical properties of a new heterodinuclear [Cr(bpy)2(H2O)(μ-O)V(C2O4)2]2·9H2O (1) complex, which contains terminal and unsupported oxo- bridge CrIII–O–VV, isolated for the first time in a molecular compound, are reported. Oxo- bridged metal units as functional intramolecular motifs exhibit interesting properties in complexes, and the discovery of new combinations of metals with different electronic configurations and redox potentials is important for the design of new materials. The reaction for the preparation of 1, involving an aqueous solution of CrIII precursor [Cr(bpy)2(H2O)2]3+ cations and VV precursor [VO2(C2O4)2]3− anions, was monitored by UV/vis spectroscopy. New absorbance bands in the 400–600 nm region can be recognized in the electronic spectrum of 1 that could originate from metal- to-metal charge transfer (MMCT). The assignment of MMCT was further supported by ATR spectroscopy under visible light irradiation. Upon exposure to visible light, a change in the intensities and positions of the absorptions bands related to vibrations of the oxo- bridged Cr–O–V moiety is observed. X-band ESR spectroscopy and magnetic susceptibility measurements point to paramagnetic behaviour of 1. The electrical response of complex 1 was studied by impedance measurements over a temperature range of −90 to 50 °C, revealing its semiconducting nature and the absence of a dielectric anomaly.

Pure and Co3+-doped BaAl2O4 [Ba(Al1–xCox)2O4, x = 0, 0.0077, 0.0379] powder samples were prepared by a facile hydrothermal route. Elemental analyses by static secondary ion mass spectrometry (SIMS), X-ray absorption spectroscopy (XAS) measurements at the Co K- edge, and X-ray diffraction studies were fully correlated, thus addressing a complete description of the structural complexity of Co3+- doped BaAl2O4 powder. Powder X-ray diffraction (PXRD) patterns indicated that prepared samples were nanocrystalline with a hexagonal P63 symmetry. The X-ray absorption near-edge structure (XANES) measurements revealed the presence of cobalt in a +3 oxidation state, while the rarely documented, tetrahedral symmetry around Co3+ was extracted from the extended X-ray absorption fine structure (EXAFS) oscillation patterns. Rietveld structure refinements showed that Co3+ preferentially substitutes Al3+ at tetrahedral Al3 sites of the BaAl2O4 host lattice, whereas the (Al3)O4 tetrahedra remain rather regular with Co3+–O distances ranging from 1.73(9) to 1.74(9) Å. The underlying magneto- structural features were unraveled through axial and rhombic zero-field splitting (ZFS) terms. The increased substitution of Al3+ by Co3+ at Al3 sites leads to an increase of the axial ZFS terms in Co3+-doped BaAl2O4 powder from 10.8 to 26.3 K, whereas the rhombic ZFS parameters across the series change in the range from 2.7 to 10.4 K, showing a considerable increase of anisotropy together with the values of the anisotropic g- tensor components flowing from 1.7 to 2.5. We defined the line between the Co3+ doping limit and influenced magneto- structural characteristics, thus enabling the design of strategy to control the ZFS terms’ contributions to magnetic anisotropy within Co3+-doped BaAl2O4 powder.

The heterodimetallic [CuFe] compounds [CuII4(terpy)4Cl5][FeIII(C2O4)3]·10H2O (1 ; terpy = 2, 2′:6′, 2′′-terpyridine), [CuII2(H2O)2(terpy)2(C2O4)][CuIIFeIII(CH3OH) (terpy)(C2O4)3]2 (2), and {; ; ; [Cu2IIFeIII(H2O) (terpy)2(C2O4)7/2]·6H2O}; ; ; n (3) were obtained using building block approach, from reaction of aqueous solution of [Fe(C2O4)3]3– and a methanol solution containing Cu2+ ions and terpy by the layering technique. Interestingly, by changing only the anion of the starting salt of copper(II), Cu(NO3)2·3H2O instead of CuCl2·2H2O, an unexpected change in the type of bridge, oxalate (2 and 3) versus chloride (1), was achieved, thus affecting the overall structural architecture. Two polymorphs of 3D coordination polymer [CuIIFeII2(H2O)(terpy)(C2O4)3]n (4), crystallizing in the triclinic (a) and monoclinic (b) space groups, were formed hydrothermally, depending on whether CuCl2·2H2O or Cu(NO3)2·3H2O was added to the water, besides K3[Fe(C2O4)3]·3H2O and terpy, respectively. Under hydrothermal conditions iron(III) from initial building block is reduced to the divalent state, creating 2D honeycomb [FeII2(C2O4)3]n2n– layers, which are bridged by [Cu(H2O)(terpy)]2+ cations. Compounds were investigated by single-crystal X- ray diffraction, IR, and impedance spectroscopies, magnetization measurements, and density functional theory (DFT) calculations. In compounds 1 and 2, 0D magnetism is observed, with 1 having a ground-state spin of 1 due to different interactions through chloride bridges of Cu2+ ions in tetramer [CuII4(terpy)4Cl5]3+ and 2 showing strong antiferromagnetic coupling of Cu2+ ions mediated by oxalate ligand in [CuII2(H2O)2(terpy)2(C2O4)]2+ and weak ones between Cu2+ and Fe3+ ions through oxalate bridge in [CuIIFeIII(CH3OH)(terpy)(C2O4)3]−. Polymer 4 exhibits antiferromagnetic phase transition at 25 K: The [FeII2(C2O4)3]n2n– layers are antiferromagnetically ordered, and a small amount of interlayer interaction is transferred through [Cu(H2O)(terpy)]2+ cations via Oox–Cu–Oox bridges. Additionally, compounds 1 and 2 are electrical insulators, while 4a and 4b show proton conductivity.

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C2O4)]&middot, 1.5H2O}n (1) (bpy = 2,2&rsquo, bipyridine) and heterodimetallic {[CrCu3(bpy)3(CH3OH)(H2O)(C2O4)4][Cu(bpy)Cr(C2O4)3]&middot, CH2Cl2&middot, CH3OH&middot, H2O}n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr2Cu2(phen)4(C2O4)6]&middot, 4CH3CN&middot, 2H2O}n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalate)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions was mediated by oxalate ligands in the chain [Mn(bpy)(C2O4)]n of 1, with intra-chain super-exchange interaction ? = (&minus, 3.134 &plusmn, 0.004) K, magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C2O4)3]nn&minus, (Cr2&ndash, Cu4) with alternating [Cr(C2O4)3]3&minus, and [Cu(bpy)]2+ units mutually bridged through the oxalate group. Another chain (Cr1&ndash, Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H2O)(&micro, C2O4)Cu(bpy)(CH3OH)]2+ (Cu1&ndash, Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1&minus, Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1&ndash, Cu3 and Cr2&ndash, Cu4. A 3D polymer {[CaCr2Cu2(phen)4(C2O4)6]&middot, 2H2O}n (3) comprising three different metal centers (Ca2+, Cr3+ and Cu2+) oxalate-bridged, contains Ca2+ atoms as nodes connected with four Cr3+ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (66) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [CuIICrIII], whose mutual interaction could possibly originate through the spin polarization of Ca2+ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C2O4)]·1.5H2O}n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu3(bpy)3(CH3OH)(H2O)(C2O4)4][Cu(bpy)Cr(C2O4)3]·CH2Cl2·CH3OH·H2O}n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C2O4)]n of 1, with intra-chain super-exchange interaction 𝐽 = (−3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C2O4)3]nn− (Cr2–Cu4) with alternating [Cr(C2O4)3]3− and [Cu(bpy)]2+ units mutually bridged through the oxalate group. Another chain (Cr1–Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H2O)(µ-C2O4)Cu(bpy)(CH3OH)]2+ (Cu1–Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1−Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1–Cu3 and Cr2–Cu4. A 3D polymer {[CaCr2Cu2(phen)4(C2O4)6]·4CH3CN·2H2O}n (3) comprising three different metal centers (Ca2+, Cr3+ and Cu2+) oxalate-bridged, contains Ca2+ atoms as nodes connected with four Cr3+ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (66) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [CuIICrIII], whose mutual interaction could possibly originate through the spin polarization of Ca2+ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.

The atomic structure, electronic structure and physical properties of $(TiZrNbCu)_{(1-x)}Ni_x$ (x $\leq$ 0.5) metallic glasses (MG) were studied in both the high-entropy (0, Comment: 40 pages, 8 figures

This study reports on the nature of electrical transport and role of structural changes induced by different type and content of TMO in Ag–containing glasses of xTMO–(30–0.5x)Ag2O–(30–0.5x)ZnO–40P2O5 (TMO = MoO3/WO3, 0 ≤ x ≤ 60 mol%) composition. Raman spectra show clustering of WO6 units in glasses with high WO3 content while the addition of MoO3 induces a gradual change of MoO6 octahedra to MoO4 tetrahedra both being cross-linked with phosphate units without clustering. For WO3 glasses, minimum in DC conductivity is observed at 30–40 mol% of WO3 for temperatures from 303 to 513 K, followed by an increase in conductivity with further WO3 addition due to an increase in polaronic contribution. Observed turnover suggests a distinct transition from predominantly ionic to predominantly polaronic transport. On the contrary, for MoO3 glasses, conductivity decreases in the whole mixed compositional range indicating that the nature of transport is dominated by ionic component throughout the measured temperature range. A comparative study of Ag+, Li+, Na+ transport in MoO3/WO3 glasses reveals a strong correlation between pre-exponential factor and activation energy, which allows detection of the prevalence of conduction mechanism. Finally, the results demonstrate that Ag2O–WO3–ZnO–P2O5 glass system is a promising electrically tunable material with significant contributions of ionic or polaronic conductivity depending on composition.

Three heterometallic oxo-bridged compounds, [Cr2(phen)4(μ-O)4Nb2(C2O4)4]·2H2O (1 ; phen = 1, 10-phenanthroline), [Cr2(terpy)2(H2O)2(μ-O)4Nb2(C2O4)4]·4H2O (2 ; terpy = 2, 2′ ; 6′, 2′′-terpyridine) and [Cr(terpy)(C2O4)(H2O)][Cr2(terpy)2(C2O4)2(μ-O)2Nb(C2O4)2]·3H2O (3), have been synthesized using a building block approach and characterized by IR spectroscopy, single-crystal and powder X-ray diffraction, magnetization measurements, and DFT calculations. The molecular structures of 1 and 2, crystallizing in P42212 and P21/n space groups, respectively, contain a square-shaped {; ; ; ; CrIII2(μ-O)4NbV2}; ; ; ; unit, while that of complex salt 3 (P[1 with combining macron] space group) consists of a mononuclear cation containing CrIII and trinuclear anions in which two CrIII ions are bridged by a –O–NbV–O– fragment. Besides hydrogen-bonding patterns resulting in a 1D- or 3D-supramolecular arrangement in 1–3, an unusual intermolecular contact has been noticed between parallel oxalate moieties occurring due to the electrostatic attraction of electron-rich carbonyl oxygen and severely electron-depleted carbon atoms in the crystal packing of 2. The antiferromagnetic coupling observed in all three compounds, determined from magnetization measurements (J = −13.51(2), −8.41(1) and −7.44(4) cm−1 for 1, 2 and 3, respectively) and confirmed by DFT calculations, originates from two CrIII ions with spin 3/2 interacting through diamagnetic –O–NbV–O– bridge(s).

Due to the wide and increasing application of engineered silver nanoparticles (AgNPs) in commercial products, their release and disposal into aquatic environmental compartments is unavoidable. The final environmental fate of AgNPs depends on their stability, behavior and lifetime in a particular system. This study aimed to systematically investigate the aggregation and dissolution behavior of AgNPs in model aquatic systems including a range of different pH values, different concentrations of mono- and divalent electrolytes, and the presence of non-ionic, anionic and cationic surfactants used in commercial detergents. The investigation was performed by a combination of surface plasmon resonance (SPR) techniques, dynamic light scattering (DLS) and electrophoretic light scattering (ELS) methods, inductively coupled plasma mass spectroscopy (ICPMS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The obtained results highlighted the importance of pH, ionic strength and interaction with surfactants relevant to the laundry cycle to the stability and environmental fate of citrate-coated AgNPs. An important implication of this study is that the interaction of AgNPs with surfactants present in wastewater effluents could potentially become more environmentally hazardous due to the increased persistence and dissolution of AgNPs.

The synthesis and properties of a novel hetero-tetranuclear compound [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H2O (1 ; bpy = 2, 2′-bipyridine), investigated by single-crystal X-ray diffraction, magnetization measurements, IR, UV/visible spectroscopy, electron paramagnetic resonance (EPR ; X- and Q-bands and high-field), and density functional theory (DFT) calculations, are reported. Crystal structure of 1 (orthorhombic Pcab space group) consists of a square-shaped macrocyclic {; ; ; ; ; Cr2(μ-O)4Nb2}; ; ; ; ; core in which CrIII and NbV ions are alternately bridged by oxo ions and three uncoordinated water molecules. The intramolecular CrIII···CrIII distances through the −O–NbV–O– bridges are 7.410(2) and 7.419(2) Å, while diagonal separation is 5.406(2) Å. The temperature dependence of magnetization M(T) evidences an anti-ferromagnetic ground state, which originates from a magnetic interaction between two CrIII ions of spin 3/2 through two triatomic −O–NbV–O– diamagnetic bridges. A spin Hamiltonian appropriate for polynuclear isolated magnetic units was used. The best-fitting curve for this model is obtained with the parameters gCr = 1.992(3), J = −12.77(5) cm–1, and |D| = 0.17(4) cm–1. The CrIII···CrIII dimer model is confirmed by EPR spectra, which exhibit a pronounced change of their shape around the temperature corresponding to the intradimer coupling J. The EPR spectra simulations and DFT calculations reveal the presence of a single-ion anisotropy that is close to being uniaxial, D = −0.31 cm–1 and E = 0.024 cm–1.

The reaction of bis(phenanthroline)metal(II) cations (M = Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) with bis(oxalato)chromium(III) anions in a water/ethanol solution gives rise to a series of compounds with oxalate-bridged cations, [{; ; M(phen)2}; ; 2(μ-C2O4)][Cr(phen)(C2O4)2]2·4H2O [Mn2Cr2 (1), Co2Cr2 (2), Ni2Cr2 (3), Cu2Cr2 (4) and Zn2Cr2 (5)]. Their structural analysis reveals that all the prepared compounds crystallize in the triclinic system, space group P[1 with combining macron], having similar unit cell parameters, molecular structures and crystal packing features. All metal centres in 1–5 are octahedrally coordinated: M2+ in homodinuclear cations are coordinated with two phen molecules and one bridging oxalate ligand ; Cr3+ in anions is coordinated with one phen ligand and two bidentate oxalate groups. The copper atom in Cu2Cr2 (4) exhibits a Jahn–Teller-distorted octahedral coordination. Owing to the considerable number of pyridyl groups present in 1–5 (from phen ligands) the crystal packing of cations and anions is driven by stacking interactions appearing in offset-face-to-face (OFF) and edge-to-face (EF) orientations. The hydrogen bonds between the anions and water molecules of crystallization form 1D ladder-like motifs. In addition to the single crystal X-ray diffraction studies, the characterization of the new complexes was accomplished by means of IR and UV/Vis spectroscopy and magnetization measurements on a SQUID magnetometer. The temperature dependence of magnetic susceptibility reveals different magnetic super exchange interactions taking place in homodinuclear oxalate-bridged cations depending on the transition metal centre (Mn2+, Co2+, Ni2+ and Cu2+). Oxalate ligands mediate the ferromagnetic coupling of Cu2+ metal cations in Cu2Cr2 (4), whereas in Mn2Cr2 (1), Co2Cr2 (2) and Ni2Cr2 (3), antiferromagnetic interactions are observed between Mn2+, Co2+ and Ni2+ cations, respectively. Also, relatively large zero-field splitting parameters for Cr3+ ions (from mononuclear anions), D ≈ 1 cm−1, were observed.

Three heterometallic one-dimensional (1D) coordination polymers {A[CrCu

Chromium niobate and tantalate (CrNbO4 and CrTaO4) were synthesized by pyrolysis of the oxalate‐based heterometallic complexes [Cr2(bpy)4(μ-O)4Nb2(C2O4)4]·3H 2O (Cr‐Nb) and [Cr(bpy)2(H2O)(μ‐O)Ta(C2O4)3]2·3.5H2O (Cr‐Ta) (bpy = 2, 2'‐bipyridine). Compared to conventional solid‐state synthesis, herein studied oxides are prepared at lower temperatures, in one step without repeating grinding procedures. The structure, morphology, and optical properties of the as‐synthesized oxides were characterized using powder X‐ray diffraction (PXRD), field emission scanning electron microscopy (SEM), the thermogravimetric and differential thermal analysis (TG/DTA) and UV‐vis diffuse reflectance spectroscopy (UV‐vis DRS). The determined band gap energies of CrNbO4 and CrTaO4 are 2.39 and 2.82 eV, respectively, which prompted us to investigate photocatalytic activity of these oxides in degradation of dyes. Microscopy studies show that the particles of both oxides began to aggregate into bigger particles, leading to an increase in grain size. Additionally, magnetization measurements on both oxides revealed spin‐glass behavior at low temperatures.

Bismuth ferrite, BiFeO3, was doped with a wide range of concentrations (0–30%) of Gd in order to investigate structural, ferroelectric, and magnetic properties and their correlation. Powder samples of Bi1-xGdxFeO3 (x = 0.00–0.30) were prepared using the hydro-evaporation synthesis method. Sintering process at 870 °C for 6 h of as-prepared, Gd doped BiFeO3 powders resulted in ceramic samples with relative densities in the range of (74–86) %. XRD analysis revealed that Bi1-xGdxFeO3 samples (x = 0.00–0.09) crystallized in rhombohedral phase; Bi1-xGdxFeO3 samples (x = 0.10–0.20) contained both rhombohedral and orthorhombic phases, while Bi1-xGdxFeO3 (x = 0.30) sample contained only the orthorhombic phase. The structural parameters obtained after Rietveld refinement for single-phase Bi1-xGdxFeO3 ceramic samples and microstructure image analysis were correlated with the results of ferroelectric and magnetic measurements. Bi1-xGdxFeO3 (x = 0.0625, 0.075, 0.09) samples showed improved ferroelectric properties and reduced leakage current density in comparison with undoped BiFeO3. Gradual increase in Gd content in BiFeO3 led to enhanced magnetic responses and weak ferromagnetic behavior.

Three heterometallic one-dimensional (1D) coordination polymers {; ; ; A[CrCu2(bpy)2(C2O4)4]·H2O}; ; ; n [A = K+ (1) and NH4+ (2) ; bpy = 2, 2’-bipyridine] and [(Cr2O7)Cu2(C2O4)(phen)2]n (3 ; phen = 1, 10- phenanthroline) with uncommon topology have been synthesized using a building block approach and characterized by single-crystal X- ray diffraction, IR and impedance spectroscopies, magnetization measurements, and DFT calculations. Due to the partial decomposition of the building block [Cr(C2O4)3]3−, all three compounds contain oxalate-bridged [Cu2(L)2(μ-C2O4)]2+ units [L = bpy (1 and 2) and phen (3)]. In compounds 1 and 2 these cations are mutually connected through oxalate groups from [Cr(C2O4)3]3−, thus forming ladderlike topologies. Unusually, three different bridging modes of the oxalate ligand are observed in these chains. In compound 3 copper(II) ions from cationic units are bridged through the oxygen atoms of Cr2O72− anions in a novel ladder-like mode. Very strong antiferromagnetic coupling observed in all three compounds, determined from the magnetization measurements and confirmed by DFT calculations (J = −343, −371 and −340 cm−1 for 1, 2 and 3, respectively), appears between two copper(II) ions interacting through the oxalate bridge.

A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high-entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and atomic volumes close to those predicted by Vegard's law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu. Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to conventional MGs with the same composition is briefly discussed.

The heterodimetallic [CuIIFeIII] one-dimensional (1D) coordination polymers {; ; ; NH4[{; ; ; Cu(bpy)}; ; ; 2(C2O4)Fe(C2O4)3]·H2O}; ; ; n (1) and {; ; ; K[{; ; ; Cu(bpy)}; ; ; 2(C2O4)Fe(C2O4)3]·H2O}; ; ; n (2) (bpy = 2, 2'-bipyridine) were obtained using a building block approach by layering technique, from the reaction of aqueous solution of [Fe(C2O4)3]3– and methanol solutions of Cu2+ and bpy. In a test tube without the presence of light partial decomposition of the tris(oxalato)ferrate(III) anion occurred yielding oxalate-bridged dinuclear [Cu(bpy)(C2O4)Cu(bpy)]2+ units. These cationic species are mutually connected through oxalate groups from [Fe(C2O4)3]3–, thus forming ladder-like topologies in compounds 1 and 2. When the same reaction mixture was exposed to daylight, initial building block [Fe(C2O4)3]3– undergoes photoreduction producing [CuIIFeII] three-dimensional (3D) coordination polymer {; ; ; [Cu(bpy)3][Fe2(C2O4)3]·H2O}; ; ; n (3a). In addition, under hydrothermal conditions, the same reduction occurs giving compound {; ; ; [Cu(bpy)3][Fe2(C2O4)3]}; ; ; n (3b), that crystallizes without water molecule. The molecular structure of 3a and 3b consist of a 3D anionic network {; ; ; [Fe2(C2O4)3]}; ; ; n2n– and tris-chelated cations [Cu(bpy)3]2+ occupying the vacancies in the framework. Very strong antiferromagnetic coupling between two copper(II) ions from [Cu(bpy)(C2O4)Cu(bpy)]2+ species transferred through oxalate bridge was determined in 1 and 2 from the magnetization measurements. In 3a and 3b strong exchange interaction is present in Fe-oxalate network, {; ; ; [Fe2(C2O4)3]}; ; ; n2n–, and the ground state of compounds tends to zero-magnetization at the lowest temperature. Additionally, the ability of compound 3a (or 3b) to act as a single-source precursor for the formation of spinel oxide was investigated by thermal analysis (TG and DTA) and powder X-ray diffraction (PXRD).

Inorganic materials that enable a link between the storage and release of molecular oxygen offer a fertile ground in continuous quest for the applications that can potentially reduce energy consumption and thus minimize adverse effects on the environment. Herein, we address reversible intake/release of an oxygen within the BaAl2O4 material as evidenced by unexpected magnetic ordering. Magnetic measurements unveil that an oxygen is stored in the form of condensed matter, creating a kind of low dimensional, chain-like assembly within the tunnels of BaAl2O4 structure. We demonstrate that oxygen is adsorbed simply by staying in air, at ambient conditions, and released relatively quickly by staying in the He or other gas atmosphere of several millibars pressure even at 300 K.

CoxMg1-xFe2O4 (where x was 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) spinel ferrites were synthesized by the sol-gel combustion method using citric acid as fuel, following the rules of propellant chemistry. Amorphous powders were then calcined at 700 °C for 3 h. Structural analysis by X-Ray diffraction (XRD), FTIR and Raman spectroscopy confirmed the formation of a cubic spinel structure where the cation distribution and inversion degree depended on the Co2+ and Mg2+ ion content. Accordingly, the lattice parameter varied between 8.3703 A (MgFe2O4) and 8.3919 A (Co0.9Mg0.1Fe2O4) as did the crystallite size, from 34 nm (Co0.1Mg0.9Fe2O4) to 48 nm (Co0.9Mg0.1Fe2O4). Scanning electron microscopy (SEM) showed the formation of multigrain agglomerates. Determined values of the maximal and remanent magnetization, as well as coercive field, depended on the Co2+ and Mg2+ ion content and increased with substitution of diamagnetic Mg2+ ions with magnetic Co2+ ions. Most impressive is the increase of the coercive field from 74 Oe for MgFe2O4 to 1000 Oe for CoFe2O4, as well as an increase of magnetization in the field of 10 kOe from 27.4 emu g−1 to 75.7 emu g−1. The determined optical band gaps from UV/Vis DRS measurements showed a strong dependence on cation content, morphology, and crystallite size, decreasing from 2.09 eV for MgFe2O4 to 1.42 eV for CoFe2O4. The photocatalytic efficiency of as-synthesized ferrites was investigated by monitoring photocatalytic degradation of Methylene Blue (MB) under natural sunlight, and artificial light source emitting visible light. Different conditions of MB degradation such as photocatalyst loading, molar concentration of MB, and pH values were investigated. Results have shown that under both visible light and natural sunlight, excessive amounts of cobalt retarded the photocatalytic process. Co0.9Mg0.1Fe2O4 showed considerable activity (74.5% after 4 h) that is unexpected but possibly connected to structural anomalies. The best photocatalytic activity under natural sunlight was achieved by MgFe2O4 (82% after 4 h), while the best photocatalytic activity under visible light was achieved by Co0.1Mg0.9Fe2O4 (79% after 4 h).

Recent studies (J. Alloys Compd. 695 (2017) 2661) of the electronic structure and properties of (TiZrNbCu)1-xNix (x ≤ 0.25) amorphous high entropy alloys (a-HEA) have been extended to x = 0.5 in order to compare behaviours of a-HEA and conventional Ni-base metallic glasses (MG). The amorphous state of all samples was verified by thermal analysis and X-ray diffraction (XRD). XRD indicated a probable change in local atomic arrangements, i.e. short-range-order (SRO) for x ≥ 0.35. Simultaneously, thermal parameters, such as the first crystallization temperature Tx and the liquidus temperature showed a tendency to saturate for x ≥ 0.35. The same tendency also appeared in the magnetic susceptibility χexp and the linear term in the low temperature specific heat γ. The Debye temperatures and Young's moduli also tend to saturate for x ≥ 0.35. These unusual changes in SRO and all properties within the amorphous phase seem correlated with the change of valence electron number (VEC) on increasing x.

Three heterometallic oxo-bridged compounds, [Cr

International audience; Heterodinuclear complexes [Cr(bpy)2(H2O)(μ-O)Ta(C2O4)3]2·3.5H2O (1) and [H2(terpy)][Cr(terpy)(C2O4)(μ-O)Ta(C2O4)3]·0.5H2C2O4·2.5H2O (2) (bpy = 2,2′-bipyridine; terpy = 2,2′6′,2′′-terpyridine) have been synthesised through a reaction of a tris(oxalate)oxotantalate(v) anion and a complex chromium(iii) cation with corresponding aromatic N-donor ligands. These are the first examples of a Cr-O-Ta bridge in molecular compounds, and the first report of heterodinuclear complexes prepared from a tris(oxalate)oxotantalate(v) anion as a building block. Structural analysis of both compounds revealed that TaV in pentagonal bipyramid geometry is connected through a slightly bent μ-O bridge to CrIII having a distorted octahedral environment. The geometry optimization performed with density functional theory (DFT) calculations gave very good agreement with the experimentally obtained structure of 1. Room temperature solid state UV-Vis spectra were recorded for both compounds and compared to those of starting reagents, in order to test for possible new electronic transitions attributed to the metal-to-metal charge transfer between CrIII and TaV through the oxo-bridge. Infrared (IR) spectroscopy supported with DFT calculations was used to assign vibrational modes to all spectral features, especially those coming from the molecular μ-oxo bridge. Temperature dependence of magnetic properties of 1 and 2 were probed with magnetic susceptibility measurements on a SQUID magnetometer. Additionally, zero-field splitting parameters were determined from electron paramagnetic resonance (EPR) spectra of compound 1 and experimentally obtained values were confirmed by DFT calculations. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

A series of seven tetranuclear Ni(II) cubane- like complexes of general formulae [Ni4L4(ROH)4] (1–3) and [Ni4L4(R1OH)x(R2OH)y] (x = y = 2 for complex 6, x = 1, y = 3 for complexes 4, 5 and 7 ; R = – C3H7, –C4H9, – C5H11 ; R1 and R2 = –CH3, –C2H5, – C3H7, –C4H9, –C5H11 ; L = N-(2-hydroxy-5- methylphenyl)salicylideneimine) were synthesized and their structural and magnetic properties were correlated in order to find out if the type of coordinated alcohol has any influence on magnetic properties. Their molecular structures reveal an octahedral coordination around nickel via five oxygen donor atoms and an imino nitrogen atom. Three out of the five oxygen atoms are derived from imine and one from the phenolate part of the Schiff base ligand, while the fifth one is derived from the neutral ROH ligand. Distortion of the cubane topology has been determined by Ni– O–Ni angle values and by O⋯Ni⋯O dihedral angle values. Intramolecular hydrogen bonds are various and rich, some are of the O–H⋯O type, spanning the cubane core and probably being one of the dominant causes of the distortion. Other weak intramolecular hydrogen bonds of the C–H⋯N type are present in complexes 1, 2, 3, 5 and 7. Very weak C–H⋯O intramolecular hydrogen bonds are responsible for the supramolecular architecture of complexes 2, 5 and 6. Intermolecular hydrogen bonds are present only in the crystal structures of complexes 2, 5 and 6. An unexpectedly high maximum of the χT(T) curve, above 20 emu K mol−1 Oe−1, is observed in some of the complexes. Significantly high χT maxima come from the quadratic spin–spin interactions depicted in the ZFS term as a consequence of the influence of the structural distortions and intermolecular interactions on the magnetic environment of Ni(II) ions. The influence of this contribution to the magnetic behaviour is revised in the known magneto- structural correlations between the values of the parameter of magnetic interaction J and the average Ni–O–Ni angle. The influence of the other structural characteristics, the average angle between O⋯Ni⋯O planes and the average angle between one O⋯Ni⋯O plane and the Ni⋯Ni vector, on the values of the parameter of magnetic interaction J is also analysed.

The results of high-field electron spin resonance (HF-ESR) spectroscopy on the title 1D coordination polymers at frequencies up to 415 GHz, supported by X-ray diffraction, thermal, magnetic susceptibility, and X-band (10 GHz) ESR studies, are presented. The heterometallic compounds {; ; SrCr2(phen)2(C2O4)4}; ; ·H2O (SrCrPhen) and {; ; SrCr2(bpy)2(C2O4)4(H2O)}; ; ·5H2O (SrCrBpy) (phen = 1, 10-phenanthroline, bpy = 2, 2′-bipyridine) were synthesized. Structural analysis revealed double oxalate-bridged zigzag Sr–Cr chains while magnetic susceptibility studies showed paramagnetic behaviour of the complexes. HF-ESR spectroscopy data were analysed with a relevant spin-Hamiltonian, yielding the g, D and E parameters of the Cr(III) ions. Both complexes showed small magnetic easy-axis type anisotropy with |D| ∼ 1 K ; SrCrBpy has uniaxial anisotropy while SrCrPhen has biaxial anisotropy. HF-ESR studies have enabled us to establish rational magneto-structural correlations and revealed significant differences between very similar crystal structures. Additionally, the ability of SrCrPhen and SrCrBpy to be single-source precursors for the formation of Sr–Cr oxides was investigated.

Bulk ceramic samples of BiFeO3 were light doped (up to 1%) with Nb5+ in the place of Fe3+ (B-site doping) and their multiferroic properties were investigated using XRD, SEM, polarization (PMTS) and magnetization (SQUID) techniques. It is shown that even the small percentages of doping can notably change electric and magnetic behavior. Electric conductivity differs by two orders of magnitude between samples doped with 0.2% and 1% Nb. The ferroelectric behavior strongly depended on conduction mechanism, and transition from space-charge-limited current (SCLC) conduction to trap-filled limited (TFL) conduction regime reflected on a change in hysteresis patterns, particularly for the samples with 0.2% and 0.5% Nb. Separation of ZFC-FC magnetization curves occurred for all Nb concentrations and increased with Nb doping. Weak ferromagnetic behavior and the increase of remnant magnetization with Nb concentration was observed from the hysteresis measurements. Coercive field changed drastically compared to the pure BiFeO3, namely, the sample with 1% Nb exhibited very high coercive magnetic field of ~ 10 kOe.

Transformation of electrical transport from ionic to polaronic in glasses, which are a potential class of new cathode materials, has been investigated in four series containing WO3/MoO3 and Li+/Na+ ions, namely: xWO3–(30−0.5x)Li2O–(30−0.5x)ZnO–40P2O5, xWO3– (30−0.5x)Na2O–(30.5x)ZnO–40P2O5, xMoO3–(30−0.5x)Li2O– (30−0.5x)ZnO–40P2O5, and xMoO3–(30−0.5x)Na2O– (30−0.5x)ZnO–40P2O5, 0 ≤ x ≤ 60, (mol%). This study reports a detailed analysis of the role of structural modifications and its implications on the origin of electrical transport in these mixed ionic-polaron glasses. Raman spectra show the clustering of WO6 units by the formation of W–O–W bonds in glasses with high WO3 content while the coexistence of MoO4 and MoO6 units is evidenced in glasses containing MoO3 with no clustering of MoO6 octahedra. Consequently, DC conductivity of tungstate glasses with either Li+ or Na+ exhibits a transition from ionic to polaronic showing a minimum at about 20-30 mol% of WO3 as a result of ion-polaron interactions followed by a sharp increase for six orders of magnitude as WO3 content increases. The formation of WO6 clusters involved in W-O-W linkages for tungsten glasses plays a key role in significant increase in DC conductivity. On the other hand, DC conductivity is almost constant for glasses containing MoO3 suggesting an independent ionic and polaronic transport pathways for glasses containing 10-50 mol% of MoO3.

A comprehensive study of selected properties of amorphous (a) Cu-TE alloys (TE=Ti, Zr and Hf) has been performed. Data for average atomic volumes of a- Cu-Hf, Ti alloys combined with literature data show that ideal solution behaviour (Vegard`s law) extends over the whole glass forming range (GFR) in all a-Cu-TE alloys. This enables one to obtain an insight into some properties and probable atomic arrangements for both, a-TEs (R. Ristić et. al., J. Alloys. Compd. 504S (2010) S194) and a-Cu by extrapolation of the data for alloys. Indeed the atomic volumes and other properties studied for all a-Cu-TE alloys extrapolate to the same values for a-Cu. Depending on the property, these values are either close to those of crystalline (c) Cu, or are close to those for liquid (L) Cu. In particular, the electronic transport properties of a-Cu seem close to those of L-Cu, whereas the static properties, such as the density of states, Young`s modulus, etc., converge to those of c-Cu. The possible impact of these results on our understanding of a-Cu-TE alloys, including glass forming ability, is discussed.

The sizes of CoMn

The sizes of CoMn2O4 nanoparticles can easily be tuned, from 40 to 8 nm, depending on the temperature of decomposition of the single-source molecular precursor {; ; ; ; [Co(bpy)3][Mn2(C2O4)3]·H2O}; ; ; ; n. The structural features of the CoMn2O4 spinel are also affected by the heat treatment temperature, showing a pronounced expansion of unit cell parameters as a consequence of thermally induced cation redistribution between tetrahedral and octahedral sites. Moreover, the magnetic behavior of CoMn2O4 was successfully tailored as well ; depending on the heat treatment, it is possible to switch between the superparamagnetic and ferrimagnetic ordering and to tailor the magnetic transition temperatures, i.e., the boundaries between the hard and soft magnetic behavior.

A correlation between the change in magnetic susceptibility ({\Delta}\c{hi}exp) upon crystallization of Cu-Zr, Hf metallic glasses (MG) with their glass forming ability (GFA) observed recently is found to apply to Cu-Ti and Zr-Ni alloys, too. In particular, a small {\Delta}\c{hi}exp , which reflects similar electronic structures, ES, of glassy and corresponding crystalline alloys, corresponds to high GFA. Here, we studied {\Delta}\c{hi}exp in five Cu-Ti and four Cu-Zr and Ni-Zr MGs. The fully crystalline final state of all alloys was verified from X-ray diffraction patterns. The variation of GFA with composition in Cu-Ti, Cu-Zr and Cu-Hf MGs was established from the variation of the corresponding critical casting thickness, dc. Due to the absence of data for dc in Ni-Zr MGs their GFA was described by using empirical criteria, such as the reduced glass transition temperature. A very good correlation between {\Delta}\c{hi}exp and dc (and/or other criteria for GFA) was observed for all alloys studied. The correlation between the ES and GFA showed up best for Cu-Zr and NiZr2 alloys where direct data for the change in ES ({\Delta}ES) upon crystallization are available. The applicability of the {\Delta}\c{hi}exp ({\Delta}ES) criterion for high GFA (which provides a simple way to select the compositions with high GFA) to other metal-metal MGs (including ternary and multicomponent bulk MGs) is briefly discussed., Comment: 29 pages, 6 figures

The influence of magnetic nanoadditives (MN) on electromagnetic properties of MgB2 wires is compared with the effects of nonmagnetic nanoadditives (NN) in bulk MgB2 and with irradiation effects in HTc tapes. Both coated (carbon, silica, or dextrin shell) and uncoated MN were used in order to assess the effects of co-doping and interparticle interaction. Transport and magnetic measurements were used in order to determine connectivity, characteristic fields (B i r r , B c2), and J c of all wires. Light doping (≤3 wt%) enhances J c and/or B i r r for all types of MN, and indicates contribution of magnetic pinning. The enhancement of J c by the best MN is comparable to that for best NN. In both MN and NN doped MgB2, matching effects in vortex pinning appear causing a maximum enhancement of B i r r at higher temperatures, but sizable enhancement persists to the lowest temperatures. Matching effects also appear in irradiated HTc tapes, but with enhancement of B i r r limited to vicinity of matching field only. The advantage of enhanced B i r r at all temperatures in doped MgB2 wires is practically annulled by poor connectivity.

Electrical transport in mixed ion-polaron glasses has been investigated in four series of glasses containing transition metal oxides (TMO) namely WO3/MoO3, and Na+/Ag+ ions with the composition xWO3-(30-0.5x)Na2O-(30-0.5x)ZnO-40P2O5, xWO3-(30-0.5x)Ag2O-(30-0.5x)ZnO-40P2O5, xMoO3-(30-0.5x)Na2O-(30-0.5x)ZnO-40P2O5, and xMoO3-(30-0.5x)Ag2O-(30-0.5x)ZnO-40P2O5, 0 ≤ x ≤ 60 (mol%). The DC conductivity of Na-glasses up to 30 mol% of WO3 and MoO3 is almost identical due to the dominance of ionic conductivity. In this compositional region, the introduction of tungstate and molybdate units increases the mobility of sodium ions and compensates the decrease in sodium number density. On the other hand, with increasing WO3 and MoO3 content and decreasing Ag+ ion concentration in Ag-glasses the DC conductivity decreases for few orders of magnitude. A significant difference in conductivity is observed for glasses with higher WO3 and MoO3 content. While for glasses containing WO3 the conductivity rapidly increases due to a huge polaronic contribution indicating a turnover from predominantly ionic to polaronic transport, the conductivity for MoO3-glasses decreases in the entire mixed compositional range suggesting dominant ionic transport. The changes in the conduction mechanism with the systematic alternation of the glass composition have been analyzed in correlation with the structural modifications and variations of molybdenum and tungsten in different oxidation states. This work is licensed under a Creative Commons Attribution 4.0 International License.

A novel heterometallic oxalate-based compound of the formula {; ; ; ; ; ; ; [Co(bpy)3][Mn2(C2O4)3]·H2O}; ; ; ; ; ; ; n (1 ; bpy = 2, 2′-bipyridine) was synthesized and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction (XRD), and magnetization measurement. The molecular structure of 1 is made of a three- dimensional (3D) anionic network, [Mn2(C2O4)3]n2n–, and tris-chelated cations [Co(bpy)3]2+ occupying the vacancies of the framework. Splitting between the zero-field-cooled (ZFC) and field-cooled (FC) branches of susceptibility below the small peak at 13 K indicates magnetic ordering. Compound 1 was used as a single-source precursor for the formation of the mixed-metal oxide CoMn2O4. This conversion via thermal decomposition was explored by thermal analysis (TGA and DTA), IR spectroscopy, powder XRD, and magnetic susceptibility measurement. From refined structural parameters, it could be seen that the spinel obtained by the thermal treatment of 1 at 800 °C is characterized by the inversion parameter δ = 21%, and therefore the structural formula at room temperature can be written as tet[Co0.79Mn0.21]oct[Co0.105Mn0.895]2O4. The temperature dependence of magnetization for CoMn2O4 points to at least three magnetic phases: the ferrimagnetic state is observed below 83 K, and up to 180 K blocking of the magnetic moments of nanocrystallites of 31 nm appears, transforming to paramagnetic-like behavior above 180 K. Microstructural characterization of the CoMn2O4 sample was carried out by means of XRD line- broadening analysis.

We present the synthesis, characterization, and magnetic properties of hematite particles in a peculiar “nanomedusa” morphology. The particles were prepared from an iron-silica complex by a hydrothermal process in a solution consisting of ethyl acetate and ethanol. The particles’ morphology, structure, and chemical composition were investigated by transmission electron microscopy, powder X-ray diffraction, and scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The “hairy” particles consist of a spherical-like core of about 100 nm diameter and fibrous exterior composed of thin “legs” of 5 nm diameter grown along one preferential direction. The particles’ cores are crystalline and undergo a magnetic phase transition to a weakly ferromagnetic state at a temperature of 930 K that matches reasonably the Néel temperature of bulk hematite. However, unlike bulk hematite that undergoes Morin transition to an antiferromagnetic state around room temperature and small hematite nanoparticles that are superparamagnetic, the “nanomedusa” particles remain weakly ferromagnetic down to the lowest investigated temperature of 2 K. Each particle thus represents a nanodimensional “hairy” ferromagnet in a very broad temperature interval, extending much above the room temperature. Such high-temperature ferromagnetic nanoparticles are not frequently found among the nanomaterials.

In the pursuit of new technologies there is exigency for novel materials with desired physical and chemical properties. Despite the fact that metal-based crystalline solids provide an access to properties that are typically unavailable or difficult to achieve in metal-free settings (i.e. magnetic or optical). Hydrogen and halogen bonds have proven to be invaluable crystal engineering tools and their use in the design of organic systems has already been well documented, but introduction of metal cations and charge- balancing entities into metal-free solids commonly disrupt well established connectivity of the key functional groups. Therefore, our aim is to study transferability of supramolecular synthons from organic to metal- organic systems, and to correlate supramolecular connectivity of metal-based building units with a number of bulk crystal properties, in particular magnetic and mechanical. For that purpose, we prepared a series of 1-D halide coordination polymers of copper(II) with the amine and amide derivatives of pyridine, pyrazine and pyrimidine. The targeted octahedral geometry was achieved for all structurally described complexes, [CuCl2(2- NH2pz)2]n, [CuCl2(2-pyz)2]n, [CuCl2(4-pym)2]n and [CuBr2(4-pym)2]n, as well as the desired connectivity via N–H×××O/N interactions. It was found that the halide ions do not have disruptive effect on the supramolecular motif C(4), which remained preserved as in purely organic systems. Antiferromagnetic spin chain behaviour, described by Bonner-Fischers model, was observed for all prepared complexes. Also, impact of the counter ion and Cu‒X···Cu angles on superexchange interaction is observed.