Hexafluoro-, heptafluoro-, and octafluoro-salts, and [MₙF₅ₙ₊₁]⁻ (n=2, 3, 4) polyfluorometallates of singly charged metal cations, Li⁺–Cs⁺, Cu⁺, Ag⁺, In⁺ and Tl⁺

The AMF₆, A₂MF₇, A₃MF₈, AM₂F₁₁, AM₃F₁₆ and AM₄F₂₁ compounds (A = Li, Na, K, Rb, Cs, Cu, Ag, In, Tl; M = P, As, V, Rh, Ru, Au, Pt, Ir, Os, Re, Sb, Mo, W, Nb, Ta, Bi) are reviewed. Some of the structural data of the AM₆ compounds are based just on powder diffraction work from the middle of the last century. The crystal structure types of AMF₆ compounds have been re-classified in this review, based mainly on single crystal data. The crystal structure types of AMF₆ compounds can be classified into six main groups: LiSbF₆ type, NaSbF₆ type, structures of cubic APF₆ and AAsF₆ with orientational disorder of the anions, tetragonal KSbF₆ (T) types and similar structures, AgSbF₆ type and similar structures, and KOsF₆ type. Reported crystal structures of A₂MF₇, A₃MF₈, AM₂F₁₁, AM₃F₁₆ and AM₄F₂₁ compounds are limited. K₂WF₇ in the orthorhombic crystal system. Among the A₃MF₈ compounds the complete crystal structure has been determined only for Na₃TaF₈, which is monoclinic. The only known examples of crystal structures of AM₂F₁₁ compounds are ASb₂F₁₁1 (A = Ag, K, Cs). Crystals of KSb₂F₁₁ are orthorhombic and isostructural to AgSb₂F₁₁, while CsSb₂F₁₁ is monoclinic. CsSb₃F₁₆ is the only example of a structurally characterized AM₃F₁₆ compound. Its crystals are orthorhombic. For the rest of the known A₂MF₇, A₃MF₈, AM₂F₁₁, AM₃F₁₆ and AM₄F₂₁ compounds, only lattice parameters are known

A unique two-dimensional silver(II) antiferromagnet Cu[Ag(SO4)2] and perspectives for its further modifications

Copper(II) silver(II) sulfate crystallizes in a monoclinic CuSO4-related structure with P21/n symmetry. This quasi-ternary compound features [Ag(SO4)2]2- layers, while the remaining cationic sites may be occupied either completely or partially by Cu2+ cations, corresponding to the formula of (CuxAg1-x)[Ag(SO4)2], x = 0.6-1.0. CuAg(SO4)2 is antiferromagnetic with large negative Curie-Weiss temperature of -84.1 K and shows two characteristic ordering phenomena at 19 K and 40 K. Density functional theory calculations reveal that the strongest superexchange interaction is a two-dimensional antiferromagnetic coupling within [Ag(SO4)2]2- layers, with the superexchange constant J2D of -11.1 meV. This renders CuAg(SO4)2 the rare representative of layered Ag2+-based antiferromagnets. Magnetic coupling is facilitated by the strong mixing of Ag d(x2-y2) and O 2p states. Calculations show that M2+ sites in MAg(SO4)2 can be occupied with other similar cations such as Zn2+, Cd2+, Ni2+, Co2+, and Mg2+.Comment: 9 pages, 4 Tables, 9 Figures, and electronic supplement of 21 page

Anomalously Large Formula Unit Volume and Its Effect on the Thermal Behavior of LiBF₄

The crystal structure of LiBF₄ has been determined by single-crystal X-ray diffraction measurements. LiBF₄ crystallizes as a merohedral twin in the trigonal space group P3₁21 with a = 4.892(5) Å, c = 11.002(12) Å, V = 228.0(4) Å3, and Z = 3 at 200 K. The twin is generated by a 2-fold rotation about the [11̄0] direction. The lithium cation is coordinated by four fluorine atoms in a distorted tetrahedral manner, wherein two Li−F distances of 1.862(5) and 1.846(5) Å are observed. The formula unit volume (FUV = V/Z) of 77.9 ų for LiBF₄ at 298 K is considerably larger than 72.7 ų for NaBF₄ and 72.5 ų for AgBF₄, despite the smaller size of Li+, indicating loose ionic packing of LiBF₄. The thermodynamic evaluation of the decomposition temperature for LiBF₄ was performed using the empirical relationship between the standard entropy and the FUV obtained. The results indicate that the large FUV of LiBF₄ contributes to its higher decomposition temperature compared to that of LiPF₆

Crystal structures of frozen room temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4), hexafluoroniobate (EMImNbF6) and hexafluorotantalate (EMImTaF6), determined by low-temperature X-ray diffraction

The crystal structures of three salts, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄), hexafluoroniobate (EMImNbF₆) and hexafluorotantalate (EMImTaF₆), all of which form room-temperature ionic liquids (RTILs), have been determined by low-temperature X-ray diffraction studies of their single crystals. EMImBF₄ crystallizes in the monoclinic space group P2₁/c with a = 8.653(5)Å, b = 9.285(18)Å, c = 13.217(7), β = 121.358(15)Å, V = 906.8(19)ų, Z = 4 at 100 K. EMImBF₄ exhibits a unique structure wherein EMIm cations form one-dimensional pillars facing the imidazolium ring to the next ring linked by H(methylene)⋯π electron interaction. The BF₄ anion also forms one-dimensional pillars along the same direction with the nearest F⋯F contact distance of 3.368(3) Å. EMImNbF₆ and EMImTaF₆ are isostructural to each other and crystallize in the orthorhombic space group P2₁2₁2₁: EMImNbF₆, a = 9.204(4)Å, b = 9.770(15)Å, c = 12.499(13)Å, V = 1124(2)ų, Z = 4 at 200 K; EMImTaF₆, a = 9.216(5)Å, b = 9.763(2)Å, c = 12.502(17)Å, V = 1124.9(17)ų, Z = 4 at 200K. In EMImNbF₆ and EMImTaF₆, EMIm cations also form a one-dimensional pillar structure and the hexafluorocomplex anions are located in a zig-zag arrangement along the same direction with the nearest F⋯F distance of 3.441(12) Å. This structure (Type-B(MF₆)) is different from the Type-A(MF₆) structure previously reported for EMImPF₆, EMImAsF₆ and EMImSbF₆. Hydrogen bonds in the Type-A(MF₆) (EMImPF₆(333 K), EMImAsF₆ (326 K) and EMImSbF₆ (283 K)) crystal lattice are weaker than those in the Type-B(MF₆) (EMImNbF₆(272 K) and EMImTaF₆ (275 K)) crystal lattice. This suggests that the strength of the hydrogen bond is not always a decisive and determining factor for the melting points of RTILs. The measurement of cell parameters for EMImBF₄ between 100 K and its melting point revealed that EMImBF₄ essentially preserves the same structure in this temperature range and increases its volume by only 4% due to the melting

Unexpected coexisting solid solutions in the quasi-binary Ag(II)F2/Cu(II)F2 phase diagram

High-temperature solid-state reaction between orthorhombic AgF2 and monoclinic CuF2 (y = 0.15, 0.3, 0.4, 0.5) in a fluorine atmosphere resulted in coexisting solid solutions of Cu-poor orthorhombic and Cu-rich monoclinic phases with stoichiometry Ag1-xCuxF2. Based on X-ray powder diffraction analyses, the mutual solubility in the orthorhombic phase (AgF2 doped with Cu) appears to be at an upper limit of Cu concentration of 30 mol % (Ag0.7Cu0.3F2), while the monoclinic phase (CuF2 doped with Ag) can form a nearly stoichiometric Cu : Ag = 1 : 1 solid solution (Cu0.56Ag0.44F2), preserving the CuF2 crystal structure. Experimental data and DFT calculations showed that AgF2 doped with Cu and CuF2 doped with Ag solid solutions deviate from the classical Vegards law. Magnetic measurements of Ag1-xCuxF2 showed that the Neel temperature (TN) decreases with increasing Cu content in both phases. Likewise, theoretical DFT+U calculations for Ag1-xCuxF2 showed that the progressive substitution of Ag by Cu decreases the magnetic interaction strength (J2D) in both structures. Electrical conductivity measurements of Ag0.85Cu0.15F2 showed a ca. 2-fold increase in specific ionic conductivity (3.71 x 10-13 plus/minus 2.6 x 10-15 S/cm) as compared to pure AgF2 (1.85 x 10-13 plus/minus 1.2 x 10-15 S/cm), indicating the formation of a vacancy- or F adatom-free metal difluoride sample.Comment: 9 pages, 4 figures, 1 Table, and electronic supplement of 14 page

The Development of Language Competences with Future Croatian Teachers within Croatian Education System

In the document "Eight key competences for life-long learning" the first and the most important competence is communication in the mother tongue. If we have good knowledge of mother tongue, then we will be better in the process of foreign language learning. Language competence means to know the language on the level of phonology, morphology, syntax, lexicology, orthography and orthoepy. We have linguistic competence (knowledge about language) and communicative competence (using of language). At this moment, when we speak about European society, it is very important to have good competences in ICT and foreign language speaking. For these reasons, we made this research about language competences in mother tongue (Croatian language) and English in primary school and the attitude of children to Croatian and English language and the way they learn them or not. The research includes 3 primary schools in Zagreb (N = 120) in the first two periods of learning (1st - 6th class). Our aim is to measure linguistic and communicative competence in Croatian and English and how pupils are different in terms of sex, age and attitude. We expect that children in the first two periods of primary school have better developed linguistic competence (theory of language) than communicative competence (using language in everyday situations). It is expected because of methods of teaching and learning. Croatian teachers are more focused on theory than functional literacy in the process of teaching and learning of Croatian language. It is easier with English because teachers of English are more focused on using English in different situations. Also, we expect better results from girls than boys, from older than younger pupils as well as from pupils who have more positive attitudes to Croatian and English language

KAgF3: quasi-one-dimensional magnetism in three-dimensional magnetic ions sublattice

The electronic structure and magnetic properties of the Jahn-Teller-distorted perovskite KAgF3 have been investigated using the full-potential linerized aug- mented plane-wave method. It is found that KAgF3 exhibits significant quasi-one- dimensional antiferromagnetism with the ratio of exchange constant jJ?j (perpen- dicular to the z axis) and J (along the z axis) about 0.04, although the sublattice of magnetic ion is three-dimensional. The strong quasi-one-dimensional antiferromag- netism originates from the C-antiferro-distortive orbital ordering of the Ag2+ 4d9 ions. The orbital ordered antiferromagnetic insulating state in KAgF3 is determined by on-site Coulomb repulsion to a large extent.Comment: 15 pages, 6 figure

Maternal Blood Levels of Toxic and Essential Elements and Birth Outcomes in Argentina: The EMASAR Study

Pregnant women’s levels of toxic and essential minerals have been linked to birth outcomes yet have not been adequately investigated in South America. In Argentina, n = 696 maternal whole blood samples from Ushuaia (n = 198) and Salta (n = 498) were collected in 2011–2012 among singleton women at 36 ± 12 h postpartum and analyzed for blood concentrations of arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb), copper (Cu), manganese (Mn), selenium (Se) and zinc (Zn). This study examined the associations between maternal elements levels and birth outcomes, and sociodemographic factors contributing to elements levels. Maternal age, parity, body mass index, smoking, and education were linked to concentrations of some but not all elements. In adjusted models, one ln-unit increase in Pb levels was associated with increased gestational age (0.2 weeks, 95% CI = 0.01–0.48) and decreased birth weight (−88.90 g, 95% CI = −173.69 to −4.11) and birth length (−0.46 cm, 95% CI = −0.85 to −0.08) in the Salta sample. Toxic elements concentrations were not associated with birth outcomes in Ushuaia participants. Birth outcomes are multifactorial problems, and these findings provide a foundation for understanding how the body burden of toxic and essential elements, within the socioeconomic context, may influence birth outcomes

Low-temperature magnetism of KAgF3

KAgF3 is a quasi-one-dimensional quantum antiferromagnet hosting a series of intriguing structural and magnetic transitions. Here we use powder neutron diffraction, μSR spectroscopy, and density functional theory calculations to elucidate the low-temperature magnetic phases. Below TN1 = 29 K we find that the material orders as an A-type antiferromagnet with an ordered moment of 0.52 μ B . Both neutrons and muons provide evidence for an intermediate phase at temperatures TN1 < T < TN2 with TN2 ≈ 66 K from a previous magnetometry study. However, the evidence is at the limit of detection and its nature remains an open problem

Low temperature magnetism of KAgF3

KAgF$_3$ is a quasi one-dimensional quantum antiferromagnet hosting a series of intriguing structural and magnetic transitions. Here we use powder neutron diffraction, $\mu$SR spectroscopy, and Density Functional Theory calculations to elucidate the low temperature magnetic phases. Below $T_{N1}=29$K we find that the material orders as an A-type antiferromagnet with an ordered moment of 0.47$\mu_{\rm B}$. Both neutrons and muons provide evidence for an intermediate phase at temperatures $T_{N1}<T<T_{N2}$ with $T_{N2}\approx 66$ K from a previous magnetometry study. However, the evidence is at the limit of detection and its nature remains an open problem.Comment: 11 pages, 8 figures. Supplementary information is included in a separate fil