Noncollinear Electric Dipoles in a Polar Chiral Phase of CsSnBr3 Perovskite.

Polar and chiral crystal symmetries confer a variety of potentially useful functionalities upon solids by coupling otherwise noninteracting mechanical, electronic, optical, and magnetic degrees of freedom. We describe two phases of the 3D perovskite, CsSnBr3, which emerge below 85 K due to the formation of Sn(II) lone pairs and their interaction with extant octahedral tilts. Phase II (77 K < T < 85 K, space group P21/m) exhibits ferroaxial order driven by a noncollinear pattern of lone pair-driven distortions within the plane normal to the unique octahedral tilt axis, preserving the inversion symmetry observed at higher temperatures. Phase I (T < 77 K, space group P21) additionally exhibits ferroelectric order due to distortions along the unique tilt axis, breaking both inversion and mirror symmetries. This polar and chiral phase exhibits second harmonic generation from the bulk and pronounced electrostriction and negative thermal expansion along the polar axis (Q22 ≈ 1.1 m4 C-2; αb = -7.8 × 10-5 K-1) through the onset of polarization. The structures of phases I and II were predicted by recursively following harmonic phonon instabilities to generate a tree of candidate structures and subsequently corroborated by synchrotron X-ray powder diffraction and polarized Raman and 81Br nuclear quadrupole resonance spectroscopies. Preliminary attempts to suppress unintentional hole doping to allow for ferroelectric switching are described. Together, the polar symmetry, small band gap, large spin-orbit splitting of Sn 5p orbitals, and predicted strain sensitivity of the symmetry-breaking distortions suggest bulk samples and epitaxial films of CsSnBr3 or its neighboring solid solutions as candidates for bulk Rashba effects.

Antiprotozoal Pt(II) Complexes as Luminophores Bearing Monodentate P/As/Sb-Based Donors: An X-ray Diffractometric, Photoluminescence, and 121Sb-Mössbauer Spectroscopic Study with TD-DFT-Guided Interpretation and Predictive Extrapolation toward Bi.

In this study, it is demonstrated that the radiative rate constant of phosphorescent metal complexes can be substantially enhanced using monodentate ancillary ligands containing heavy donor atoms. Thus, the chlorido coligand from a Pt(II) complex bearing a monoanionic tridentate C^N*N luminophore ([PtLCl]) was replaced by triphenylphosphane (PPh3) and its heavier pnictogen congeners (i.e., PnPh3 to yield [PtL(PnPh3)]). Due to the high tridentate-ligand-centered character of the excited states, the P-related radiative rate is rather low while showing a significant boost upon replacement of the P donor by heavier As- and Sb-based units. The syntheses of the three complexes containing PPh3, AsPh3, and SbPh3 were completed by unambiguous characterization of the clean products using exact mass spectrometry, X-ray diffractometry, bidimensional NMR, and 121Sb-Mössbauer spectroscopy (for [PtL(SbPh3)]) as well as steady state and time-resolved photoluminescence spectroscopies. Hence, it was shown that the hybridization defects of the Vth main-group atoms can be overcome by complexation with the Pt center. Notably, the enhancement of the radiative rate constants mediated by heavier coligands was achieved without significantly influencing the character of the excited states. A rationalization of the results was achieved by TD-DFT. Even though the Bi-based homologue was not accessible due to phenylation side reactions, the experimental data allowed a reasonable extrapolation of the structural features whereas the hybridization defects and the excited state properties related to the Bi-species and its phosphorescence rate can be predicted by theory. The three complexes showed an interesting antiprotozoal activity, which was unexpectedly notorious for the P-containing complex. This work could pave the road toward new efficient materials for optoelectronics and novel antiparasitic drugs.

Oxidation of europium with ammonium perfluorocarboxylates in liquid ammonia: pathways to europium(II) carboxylates and hexanuclear europium(III) fluoridocarboxylate complexes.

The novel coordination polymer [Eu(O2CCF3)2(dmf)2]∞ (1) (dmf = N,N-dimethylformamide) containing europium(II) and the two new compounds (NH4)2[Eu6F8(O2CCF3)12(CF3COOH)6] (2) and (NH4)2[Eu6F8(O2CC2F5)12(C2F5COOH)6]·8C2F5COOH (3), both based on hexanuclear europiate(III) complexes, were synthesized from precursors with a Eu2+ : Eu3+ ratio >1, obtained by reaction of europium metal with ammonium perfluorocarboxylates in liquid ammonia. In the crystal structure of 1 the europium(II) ions are bridged by carboxylate groups and N,N-dimethylformamide to form polymeric chains with Eu2+⋯Eu2+ distances of 408.39(13)-410.49(13) pm. The compound crystallizes in the triclinic space group P1̄ (Z = 2). To the best of our knowledge, this is the first example of a (solvated) perfluorocarboxylate containing a lanthanoid in a subvalent oxidation state. In the crystal structures of 2 and 3 the europium(III) ions are bridged by fluoride ions and carboxylate groups to form hexanuclear complex anions with an octahedral arrangement of the cations. The Eu3+⋯Eu3+ distances are in the range of 398.27(15)-400.93(15) pm in 2 and 395.37(4)-399.78(5) pm in 3, respectively. Both compounds crystallize in the monoclinic space group type P21/n (Z = 4) and are the first examples of octahedro-hexanuclear europium carboxylates for which fluoride is reported as a bridging ligand. In all compounds the oxidation state of europium was monitored via151Eu Mössbauer and photoluminescene spectroscopy.

The tin sulfates Sn(SO4)2 and Sn2(SO4)3: crystal structures, optical and thermal properties.

We report the crystal structures of two tin(IV) sulfate polymorphs Sn(SO4)2-I (P21/c (no. 14), a = 504.34(3), b = 1065.43(6), c = 1065.47(6) pm, ß = 91.991(2)°, 4617 independent reflections, 104 refined parameters, wR2 = 0.096) and Sn(SO4)2-II (P21/n (no. 14), a = 753.90(3), b = 802.39(3), c = 914.47(3) pm, ß = 92.496(2)°, 3970 independent reflections, 101 refined parameters, wR2 = 0.033). Moreover, the first heterovalent tin sulfate Sn2(SO4)3 is reported which adopts space group P1̄ (no. 2) (a = 483.78(9), b = 809.9(2), c = 1210.7(2) pm, α = 89.007(7)°, ß = 86.381(7)°, γ = 73.344(7)°, 1602 independent reflections, 152 refined parameters, wR2 = 0.059). Finally, SnSO4 - the only tin sulfate with known crystal structure - was revised and information complemented. The optical and thermal properties of all tin sulfates are investigated by FTIR, UV-vis, luminescence and 119Sn Mössbauer spectroscopy as well as thermogravimetry and compared.

Cu2ZnSbS4: A Thioantimonate(V) with Remarkably Strong Covalent Sb-S Bonding.

A new member to the A2IBIICIVX4 compound family, Cu2ZnSbS4, was synthesized successfully using ball milling and postannealing in H2S-atmosphere. For comparative purposes, Cu3SbS4 was additionally prepared using the same synthetic approach. As is common for A2IBIICIVX4 compounds, Cu2ZnSbS4 crystallizes isostructural to Cu3SbS4 in the stannite-type structure in space group I42m. Both antimony sulfides contain monovalent diamagnetic copper and are characterized by substantial covalent bonding. This is consistent with the 121Sb isomer shifts occurring for the Mössbauer spectra of Cu2ZnSbS4 (-7.71 mm s-1) and Cu3SbS4 (-7.68 mm s-1) which fall in the region of covalently bonded Sb(V) compounds. These spectroscopic results are supported by electronic structure calculations.

Synthesis and Hydrogenation of Heavy Homologues of Rhodium Carbynes: [(Me3 P)2 (Ph3 P)Rh≡E-Ar*] (E=Sn, Pb).

Tetrylidynes [(Me3 P)2 (Ph3 P)Rh≡SnAr*] (10) and [(Me3 P)2 (Ph3 P)Rh≡PbAr*] (11) are accessed for the first time via dehydrogenation of dihydrides [(Ph3 P)2 RhH2 SnAr*] (3) and [(Ph3 P)2 RhH2 PbAr*] (7) (Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl), respectively. Tin dihydride 3 was either synthesized in reaction of the dihydridostannate [Ar*SnH2 ]- with [(Ph3 P)3 RhCl] or via reaction between hydrides [(Ph3 P)3 RhH] and 1 / 2 [(Ar*SnH)2 ]. Homologous lead hydride [(Ph3 P)2 RhH2 PbAr*] (7) was synthesized analogously from [(Ph3 P)3 RhH] and 1 / 2 [(Ar*PbH)2 ]. Abstraction of hydrogen from 3 and 7 supported by styrene and trimethylphosphine addition yields tetrylidynes 10 and 11. Stannylidyne 10 was also characterized by 119 Sn Mössbauer spectroscopy. Hydrogenation of the triple bonds at room temperature with excess H2 gives the cis-dihydride [(Me3 P)2 (Ph3 P)RhH2 PbAr*] (12) and the tetrahydride [(Me3 P)2 (Ph3 P)RhH2 SnH2 Ar*] (14). Complex 14 eliminates spontaneously one equivalent of hydrogen at room temperature to give the dihydride [(Me3 P)2 (Ph3 P)RhH2 SnAr*] (13). Hydrogen addition and elimination at stannylene tin between complexes 13 and 14 is a reversible reaction at room temperature.

Formation of monomeric Sn(ii) and Sn(iv) perfluoropinacolate complexes and their characterization by 119Sn Mössbauer and 119Sn NMR spectroscopies.

The synthesis and characterization of a series of Sn(ii) and Sn(iv) complexes supported by the highly electron-withdrawing dianionic perfluoropinacolate (pinF) ligand are reported herein. Three analogs of [SnIV(pinF)3]2- with NEt3H+ (1), K+ (2), and {K(18C6)}+ (3) counter cations and two analogs of [SnII(pinF)2]2- with K+ (4) and {K(15C5)2}+ (5) counter cations were prepared and characterized by standard analytical methods, single-crystal X-ray diffraction, and 119Sn Mössbauer and NMR spectroscopies. The six-coordinate SnIV(pinF) complexes display 119Sn NMR resonances and 119Sn Mössbauer spectra similar to SnO2 (cassiterite). In contrast, the four-coordinate SnII(pinF) complexes, featuring a stereochemically-active lone pair, possess low 119Sn NMR chemical shifts and relatively high quadrupolar splitting. Furthermore, the Sn(ii) complexes are unreactive towards both Lewis bases (pyridine, NEt3) and acids (BX3, Et3NH+). Calculations confirm that the Sn(ii) lone pair is localized within the 5s orbital and reveal that the Sn 5px LUMO is energetically inaccessible, which effectively abates reactivity.

On the phosphors Na5M(WO4)4 (M = Y, La-Nd, Sm-Lu, Bi) - crystal structures, thermal decomposition, and optical and magnetic properties.

The pentasodium rare-earth tungstates Na5M(WO4)4 are closely related to the sodium rare-earth double tungstates Na5M(WO4)2 both adopting the scheelite structure type (space group I41/a, no. 88). After the preparation of polycrystalline powders via flux syntheses improving the phase purity significantly, the crystal structures of Na5M(WO4)4 (M = Y, La-Nd, Sm-Lu, Bi) were determined by single crystal XRD and Rietveld analysis. Na5M(WO4)4 is a promising phosphor material both as a host and as a 100% phosphor due to the possible charge transfer of the tungstate group and the absence of any concentration quenching. Na5M(WO4)4 incongruently melts to Na5M(WO4)2 and Na2WO4. After the clarification of the crystallographic relationship of Na5M(WO4)4 and Na5M(WO4)2 based on a rare isomorphic transition of index 5 (i5) the non-linear trend of the decomposition temperature within the row of rare earth ions is explained systematically taking into account the existence of domains within the crystal structure predetermining the posterior decomposition. A miscibility gap for solid solutions of Na5Y(WO4)4 and Na5Eu(WO4)4 or Na5Tb(WO4)4 is identified and its temperature dependence is investigated. Furthermore, the investigation of the fluorescent properties of Na5M(WO4)4 (M = Pr, Sm, Eu, Tb, Tm, Bi), Na5Y1-xEux(WO4)4 and Na5Y1-yTby(WO4)4 provided insights into the weak ligand field and the energy transfer from WO42- to M3+ governed by the emission of the sensitiser within Na5M(WO4)4. Additionally, the compounds were characterised by magnetic measurements and vibrational, UV/Vis and 151Eu Mössbauer spectroscopy.

Synthesis, electronic structure and physical properties of two new layered compounds, EuFAgSe and EuFAg1-δTe, featuring the active redox pair Eu2+/Ag.

Systematic studies of the ZrCuSiAs (also LaOAgS or 1111) structure type resulted in the synthesis of two new fluoride chalcogenides, EuFAgSe and EuFAg1-δTe, whereas their sulfide analog, EuFAgS, could not be obtained. Both new compounds are tetragonal, P4/nmm, with cell parameters a = 4.1542(1) Å, c = 9.2182(1) Å for the selenide and a = 4.3255(1) Å, c = 9.5486(1) Å for the telluride. Rietveld refinement reveals a significant silver deficiency in the telluride (δ = 0.05), while the selenide is nearly stoichiometric. Both compounds are semiconductors as shown by diffuse reflectance spectroscopy and confirmed by density-functional calculations of the band structure. Magnetism of both compounds is predominantly driven by Eu2+, as indicated by magnetic susceptibility measurements and corroborated by 151Eu Mössbauer spectroscopy. EuFAg1-δTe and EuFAgSe are paramagnetic down to 1.8 K.

Structural Peculiarities and Thermoelectric Study of Iron Indium Thiospinel.

The homogeneity range of ternary iron indium thiospinel at 873 K was investigated. A detailed study was focused on two distinct series (y=z): 1) a previously reported charge-balanced (In0.67+0.33y □0.33-0.33y )tetr [In2-z Fez ]oct S4 (A1-series; □ stands for vacancy; the abbreviations "tetr" and "oct" indicate atoms occupying tetrahedral 8a and octahedral 16d sites, respectively) and 2) a new charge-unbalanced (In0.67+y □0.33-y )tetr [In2-z Fez ]oct S4 (A2-series). Fe atoms were confirmed to exclusively occupy an octahedral position in both series. An unusual reduction of the unit cell parameter with increasing Fe content is explained by differences in the ionic radii between Fe and In, as well as by an additional electrostatic attraction originating from charge imbalance (latter only in A2-series). The studied compound is an n-type semiconductor, and its charge carrier concentration increases or decreases for larger Fe content within the A1- and A2-series, respectively. The thermal conductivity κtot is significantly reduced upon increasing vacancy concentration, whereas the change of power factor is insufficient to drastically improve the thermoelectric figure of merit.

From 3D to 2D: Structural, Spectroscopic and Theoretical Investigations of the Dimensionality Reduction in the [PtAl2 ]δ- Polyanions of the Isotypic MPtAl2 Series (M=Ca-Ba, Eu).

Four new MPtAl2 (M=Ca, Sr, Ba, Eu) compounds, adopting the orthorhombic MgCuAl2 -type structure, have been synthesized from the elements using tantalum ampoules. All compounds are obtained as platelet-shaped crystallites and exhibit an increasing moisture sensitivity with increasing size of the formal M cation. Structural investigations indicate a pronounced elongation of the crystallographic b-axis, which results in a significant distortion of the [PtAl2 ]δ- polyanion. Within the polyanion, layer-like arrangements can be found with bonding Pt-Al interactions within the slab; the increase of the b-axis can be attributed to increasing Al-Al distances and therefore decreasing interactions between the slabs, caused by the differently-sized formal M cations. While the alkaline earth (M=Ca, Sr) representatives exhibit Pauli paramagnetism, BaPtAl2 shows diamagnetic behavior, finally EuPtAl2 is ferromagnetic with TC =54.0(5) K. The effective magnetic moment indicates that the Eu atoms are in a divalent oxidation state, which is confirmed by 151 Eu Mössbauer spectroscopic investigations. Measurements below the Curie-temperature show a full magnetic hyperfine field splitting with Bhf =21.7(1) T. 27 Al and 195 Pt magic-angle spinning NMR spectroscopy corroborates the presence of single crystallographic sites for the Pt and Al atoms. The large 27 Al nuclear electric quadrupolar coupling constants confirm unusually strong electric field gradients, in agreement with the structural distortions and the respective theoretical calculations. X-ray photoelectron spectroscopy has been utilized to investigate the charge transfer within the polyanion. The Pt 4f binding energy decreases with decreasing electronegativity / ionization energy of the alkaline earth elements, suggesting an increasing electron density at the Pt atoms. Theoretical investigations underline the platinide character of the investigated compounds by Bader charge calculations. The analysis of the integrated crystal orbital Hamilton population (ICOHP) values, electron localization function (ELF) and isosurface analyses lead to a consistent structural picture, indicating stable layer-like arrangements of the [PtAl2 ]δ- polyanion.

Diluting europium spins - a magnetic and 151Eu Mössbauer spectroscopic investigation of the solid solution Eu1-xSrxPtIn2.

The indide EuPtIn2 (MgCuAl2 type, Cmcm, a = 448.23(4), b = 1068.64(11), c = 784.09(8) pm, wR2 = 0.0432, 466 F2 values, 16 variables) was synthesized by induction-melting of the elements and subsequent annealing. The platinum and indium atoms built up a three-dimensional [PtIn2]2- polyanionic network (278-282 pm Pt-In) which contains channels that are filled with the europium cations. These bind to the network through shorter Eu-Pt contacts (302-323 pm). Temperature dependent magnetic susceptibility and 151Eu Mössbauer spectroscopic data manifest divalent europium down to 4.2 K. EuPtIn2 orders ferromagnetically at 32.5 K. EuPtIn2 and SrPtIn2 form a complete solid solution Eu1-xSrxPtIn2 with Vergard type behavior for the lattice parameters. Divalent europium is proven through magnetic data and Mössbauer spectroscopy. The Curie temperature decreases monotonically from 32.5 to 3.1 K in going to Eu0.1Sr0.9PtIn2.

An Unusual Valence State: Trivalent Europium in Intermetallic Eu2 Ir3 Al9.

Eu2 Ir3 Al9 , synthesized from the elements in tantalum tubes, is one of the rare examples for trivalent europium in the field of intermetallic compounds. The compound crystallizes in the Y2 Co3 Ga9 -type structure (space group Cmcm), with lattice parameters fitting in between the isostructural samarium and gadolinium compounds. In the crystal structure, the Eu atoms form Al3 -triangle-centered honeycomb layers and exhibit a coordination number of 17 in the shape of a fivefold-capped hexagonal prism (Eu@Ir6 Al6 +Al5 ). Magnetic measurements indicate an overall low susceptibility, in line with van Vleck paramagnetism caused by the Eu3+ cations. Fits of the susceptibility yield a coupling constant of λ=290(10) K and an effective magnetic moment of µeff =4.56(1) µB , in line with a slight hybridization of the 7 F0 and 7 F1 state. 151 Eu Mössbauer spectroscopic investigations unambiguously prove the presence of solely Eu3+ in the bulk material.