Single-crystal Raman Spectroscopy Research Articles

The isotypic series of tetragonal lanthanoid(III) fluoride oxoarsenates(III) Ln 5F3[AsO3]4 (Ln = Eu–Lu)

Abstract The new fluoride-containing lanthanoid(III) oxoarsenates(III) with the composition Ln 5F3[AsO3]4 (Ln = Eu–Lu) could be obtained through partial metallothermic reduction from mixtures of the corresponding trifluorides (LnF3) and the metals (Ln) with As2O3 upon heating in fused silica ampoules. They all crystallize tetragonally in the space group P4/ncc with lattice parameters ranging from a = 1164.71(8) pm and c = 1097.95(7) pm for Eu5F3[AsO4]4 down to a = 1125.72(8) pm and c = 1061.16(7) pm for Lu5F3[AsO3]4 for Z = 4 as consequence of the lanthanoid contraction. The crystal structure exhibits three positions for the trications occupied by one As3+ and two Ln 3+ species. The lanthanoids occur with two different coordination polyhedra consisting of a fluoride-capped oxygen cube [(Ln1)O8F]14− and a bicapped trigonal prism [(Ln2)O6F2]11− of F− and O2− anions. A surprisingly diverse Ln 3+ cation coordination for the F− anions is noteworthy, as (F1)− has contact to five, but (F2)− to only two of them. The crystallographically unique As3+ cation is coordinated in a discrete ψ 1-tetrahedron [AsO3]3− by three oxygen atoms. The lone-pairs of electrons at the As3+ centers point into empty channels along [001], flanked by four columns of condensed [(Ln1)O8F]14− polyhedra. As rather short oxygen-fluorine distances are present within this structural feature, the absence of (OH)− units apt to replace F− needed to be verified by single-crystal Raman spectroscopy. The composition Ln 5F3[AsO3] was also confirmed by electron-beam microprobe (EDXS) measurements and the phase purity of selected samples could be proven by powder X-ray diffractometry (PXRD).

Formation of Peroxynitrite, [O-N-O-O]-, via a Cascade of Reactions between Ozonide and Ammonia.

We report on an unexpected reaction between ammonia and potassium ozonide dissolved in liq. NH3 resulting in the formation of peroxynitrite, [ONOO]-, which exclusively happens in the presence of a specific partially fluorinated aniline-based ammonium cation. High-resolution structural data of the peroxynitrite anion in cis-conformation have been obtained. We further studied this molecule anion by single crystal Raman spectroscopy. The cis and trans isomers of peroxynitrite were analysed computationally with respect to their relative energies, the cis-trans transition barrier and their decomposition pathways to the nitrate anion. By experimentally examining cations decorated with fluorine ligands to different degrees, we demonstrate that fluorine specific interactions play a crucial role in the unexpected formation of peroxynitrite and as a conspicuously structure directing factor for the underlying crystalline solid phases, exhibiting distinct micro-separations of fluorine and hydrogen enriched regions.

Structural Capture of η1-OSO to η2-(OS)O Coordination Isomerism in a New Ruthenium-Based SO2-Linkage Photoisomer That Exhibits Single-Crystal Optical Actuation.

Recent discoveries of a range of single-crystal optical actuators are feeding a new form of materials chemistry, given their broad range of potential applications, from light-induced molecular motors to light sensors and optical-memory media. A series of ruthenium-based coordination complexes that exhibit sulfur dioxide linkage photoisomerization is of particular interest because they exhibit single-crystal optical actuation via either optical switching or nano-optomechanical transduction processes. We report the discovery of a new complex in this series of chemicals, [Ru(SO2)(NH3)4(3-fluoropyridine)]tosylate2 (1), which forms an η1-OSO photoisomer with 70% photoconversion upon the application of 505 nm light. The uncoordinated oxygen atom in this η1-OSO photoisomer impinges on one of the arene rings in a neighboring tosylate counter ion of 1 just enough that incipient nano-optomechanical transduction is observed. The structure and optical properties of this actuator are characterized via in situ light-induced single-crystal X-ray diffraction (photocrystallography), single-crystal optical absorption spectroscopy and microscopy, as well as single-crystal Raman spectroscopy. These materials-characterization methods were also used to track thermally induced reverse isomerization processes in 1. One of these processes involves an η1-OSO to η2-(OS)O transition, which was found to proceed sufficiently slowly at 110 K that its structural mechanism could be determined via a time sequence of photocrystallography experiments. The resulting data allowed us to structurally capture the transition, which was shown to occur via a form of coordination isomerism. Our newfound knowledge about this structural mechanism will aid the molecular design of new [RuSO2] complexes with functional applications.

The Na2−nHn[Zr(Si2O7)]∙mH2O Minerals and Related Compounds (n = 0–0.5; m = 0.1): Structure Refinement, Framework Topology, and Possible Na+-Ion Migration Paths

The Na2−nHn[Zr(Si2O7)]∙mH2O family of minerals and related compounds (n = 0–0.5; m = 0.1) consist of keldyshite, Na3H[Zr2(Si2O7)2], and parakeldyshite, Na2[Zr(Si2O7)], and synthetic Na2[Zr(Si2O7)]∙H2O. The crystal structures of these materials are based upon microporous heteropolyhedral frameworks formed by linkage of Si2O7 groups and ZrO6 octahedra with internal channels occupied by Na+ cations and H2O molecules. The members of the family have been studied by the combination of theoretical (geometrical–topological analysis, Voronoi migration map calculation, structural complexity calculation), and empirical methods (single-crystal X-ray diffraction, microprobe analysis, and Raman spectroscopy for parakeldyshite). It was found that keldyshite and parakeldyshite have the same fsh topology, while Na2ZrSi2O7∙H2O is different and has the xat topology. The microporous heteropolyhedral frameworks in these materials have a 2-D system of channels suitable for the Na+-ion migration. The crystal structure of keldyshite can be derived from that of parakeldyshite by the Na+ + O2− ↔ OH− + □ substitution mechanism, widespread in the postcrystallization processes in hyperagpaitic rocks.

Synthesis, structural, thermal, Hirshfeld surface and DFT studies on a new hybrid compound: bis[4-(dimethylamino)pyridinium] tetrachloridomanganate(II)

A new organic-inorganic hybrid compound (1) based on 4-(dimethylamino)pyridine and manganese(II), MnCl4(C7H11N2)2, has been synthesized and its structure determined by single-crystal X-ray diffraction, infrared and Raman spectroscopy, Hirshfeld and thermal analysis. At room temperature, 1 crystallizes in the centrosymmetric space group P-1. The structure is built up on isolated [MnCl4]2- anions and 4-(dimethylamino)pyridinium (C7H11N2)+ cations connected by a network of N–H···Cl, C–H···Cl, and π-π supramolecular interactions. The 3 D Hirshfeld surface calculations were performed to investigate the quantitatively relative contribution of these interactions in the crystal packing. The thermal behavior of 1 was characterized by TGA/DTA analysis and Density Functional Theory (DFT); there is a good comparison between the experimental and computed results.

Attributions of rich Raman modes and their temperature dependences in Mn4Nb2O9 single crystals

It is an important task of single crystal Raman spectroscopy to identify the lattice vibration modes in terms of symmetry and further study the temperature-dependent behavior of various Raman modes. A4B2O9 (A = Co, Mn, Fe; B = Nb, Ta) type magnetodielectric or magnetoelectric materials represented by Mn4Nb2O9 not only have high structural anisotropy, but also have strong electron-phonon or spin-phonon coupling, which is very meaningful for the Raman scattering study. Here, we conduct the first investigation of the angle and temperature-dependent Raman scattering behaviors in highly crystalline Mn4Nb2O9 crystals with perfect a-cut. Polarization experiments show that most of the Raman peaks can be clearly identified as A1g and Eg vibration modes, showing a clear anisotropic structure. As the temperature increases from 83 K to 283 K, the Raman shifts of most Raman peaks of Mn4Nb2O9 exhibit a linear softening behavior with the temperature coefficient in the range of −0.010 cm−1 K−1 to −0.015 cm−1 K−1. No remarkable change of Raman shifts occurs at antiferromagnetic (AFM) transition nearby, indicating that the change of the ion position in the AFM transition has little effect on its Raman scattering behavior.

Crystal-Chemical Properties of Synthetic Almandine-Pyrope Solid Solution by X-Ray Single-Crystal Diffraction and Raman Spectroscopy

Crystal-chemical properties of synthetic Almandine-Pyrope (Alm-Pyr) solid solutions were investigated by X-ray single-crystal diffraction and Raman spectroscopy. Garnet solid solution with different compositions were synthesized from powder at 4.0 GPa and annealed at 1200 °C for 48 h by a multi-anvil pressure apparatus. Garnet crystals with different sizes (about 60–1000 μm) were obtained from synthesis. The results of X-ray single-crystal diffraction show that the unit cell constants decrease with increasing Pyr contents in the synthetic Alm-Pyr crystals due to the smaller ionic radius of Mg2+ in eightfold coordination than that of Fe2+. The data exhibit obviously positive deviations from ideal mixing volumes across the Alm-Pyr join which may be caused by the distortion of the SiO4 tetrahedron. Moreover, the significant decrease in the average M-O bond length and volume of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell constant and volume. On the other hand, selected bond distances (average <M-O>, <Al-O>, and <D-O> distances) have a linear correlation with the unit-cell parameter, but the <Si-O> distance has nonlinear correlation. With increasing the unit-cell parameter, the average <M-O> distance increases significantly, followed by the average <D-O> and <Al-O> distances. While the <Si-O> distance changes negligibly further confirming the conclusion that the significant decrease of the average M-O bond length of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell volume. In the Raman spectra collected for the Alm-Pyr solid solutions, Raman vibration mode assignments indicate that the Raman vibrational spectra change along the Alm-Pyr binary solution. The mode frequencies of Si-O stretching, Si-O bending, and the rotation of the SiO4-tetrahedron (R(SiO4)) decrease linearly, while the translational modes of the SiO4-tetrahedron (T(SiO4)) increase with increasing Alm contents.

Local-scale structural response of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 to external electric fields

The local structure and atomic dynamics of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 with x ranging from 0 to 0.074 were analyzed at room temperature by in situ single-crystal Raman spectroscopy under an external dc electric field E applied along the pseudocubic [100]c or [110]c directions, to gain further insights into the atomistic mechanism of polar coupling near the morphotropic phase boundary (MPB). The results reveal a striking compositional dependence of the E[100]c-induced changes in the Raman scattering and suggest that the origin of the enhanced longitudinal piezoelectric coefficient in alkali-Bi based solid solutions with a pseudocubic structure near MPB is due to the composition-driven reduction of the local strains and the consequent enhancement of the structural flexibility under external stimuli.

Equation of State and Amorphization of Ca9R(VO4)7 (R = La, Nd, Gd): A Combined High-Pressure X-ray Diffraction and Raman Spectroscopy Study.

Ca9R(VO4)7 (R = rare earth) multicomponent oxides of a whitlockite-related structure are under consideration for applications in optoelectronics. In this work, the Czochralski-grown Ca9R(VO4)7 crystals were investigated as a function of pressure by powder X-ray diffraction and single-crystal Raman spectroscopy. The diffraction experiments were performed at the ALBA synchrotron under pressures ranging up to 9.22(5), 10.7(1), and 8.55(5) GPa for R = La, Nd, and Gd, respectively, to determine the third order equation of state (EOS) parameters. Fitting of the Birch-Murnaghan EOS provided the isothermal bulk moduli K0 = 63(4), 63(2), and 61(5) GPa for these three orthovanadates. These values are apparently lower than that reported for structurally related tricalcium vanadate Ca3(VO4)2. The compressibility anisotropy was observed; the lattice is markedly stiffer in [001] than in [100] direction. For Ca9Nd(VO4)7, the variation of the diffractograms just above 10 GPa provides an indication on the beginning of amorphization process; during pressure release the whitlockite-like structure is recovered. Raman spectroscopy measurements for single crystals of the above-mentioned rare-earth vanadates and Ca9Y(VO4)7 were performed (the maximum pressures achieved were 16.3(1), 21.2(1), 15.3(1), and 18.6(1) GPa for R = Y, La, Nd, and Gd, respectively). These measurements reveal a partially reversible phase transition interpreted as amorphization, with an onset at the pressure of ∼9-10 GPa, characterized by broadening of the peaks and their shift to lower energies.

Investigation of Large Polychloride Anions: [Cl11 ]- , [Cl12 ]2- , and [Cl13

For decades the chemistry of polyhalides was dominated by polyiodides and more recently also by an increasing number of polybromides. However, apart from a few structures containing trichloride anions and a single report on an octachloride dianion, [Cl8 ]2- , polychlorine compounds such as polychloride anions are unknown. Herein, we report on the synthesis and investigation of large polychloride monoanions such as [Cl11 ]- found in [AsPh4 ][Cl11 ], [PPh4 ][Cl11 ], and [PNP][Cl11 ]⋅Cl2 , and [Cl13 ]- obtained in [PNP][Cl13 ]. The polychloride dianion [Cl12 ]2- has been obtained in [NMe3 Ph]2 [Cl12 ]. The novel compounds have been thoroughly characterized by NMR spectroscopy, single-crystal Raman spectroscopy, and single-crystal X-ray diffraction. The assignment of their spectra is supported by molecular and periodic solid-state quantum-chemical calculations.

Copper(I) bromide and chloride complexes with urotropine and triethylenediamine: synthesis, crystal structure, and Raman characterization

In the present study, the oxidative dissolution of metallic copper has been explored with the intention to prepare some new complexes with urotropine (hmta) and triethylenediamine (dabco) ligands. All the compounds synthesized were characterized by single-crystal X-ray diffraction and Raman spectroscopy. Reactions performed in a DMSO/CuCl2∙2H2O mixture resulted in [(μ-Cl)2CuI(hdabco+)CuI(μ-Cl)(κS-DMSO)]n and [CuICl(hmta)2] complexes. Their isostructural bromide analogs [(μ-Br)2CuI(hdabco+)CuI(μ-Br)(κS-DMSO)]n and [CuIBr(hmta)2] were prepared by the reaction of elemental copper with respective ligands in a DMSO/CBr4 mixture. Early interrupted reaction of the copper wire with the DMSO/CBr4/dabco solution resulted in an appearance of crystals of the [CuI2Br2(CO)2(dabco)]n carbonyl complex on the copper surface. It arises with the participation of in situ formed carbon monoxide. Despite the identical stoichiometry, the crystal structure of the [Cu2Br2(CO)2(dabco)]n complex is markedly different from that of a known [Cu2Cl2(CO)2(dabco)]n analog.

Sc2[Se2O5]3: The First Rare-Earth Metal Oxoselenate(IV) with Exclusively [Se2O5]2− Anions

The scandium oxodiselenate(IV) Sc2[Se2O5]3 was synthesized via solid-state reactions between scandium sesquioxide (Sc2O3) and selenium dioxide (SeO2) with thallium(I) chloride (TlCl) as fluxing agent in molar ratios of 1:4:2. Evacuated fused silica ampoules were used as reactions vessels for annealing the mixtures for five days at 800 °C. The new scandium compound crystallizes in the triclinic space group P 1 ¯ with the lattice parameters a = 663.71(5) pm, b = 1024.32(7) pm, c = 1057.49(8) pm, α = 81.034(2)°, β = 87.468(2)°, γ = 89.237(2)° and Z = 2. There are two distinct Sc3+ positions, which show six-fold coordination by oxygen atoms as [ScO6]9− octahedra (d(Sc–O) = 205–212 pm). Three different [Se2O5]2− anions provide these oxygen atoms with their terminal ligands (Ot). Each of the six selenium(IV) central atoms exhibit a stereochemically active lone pair of electrons, so that all [Se2O5]2− anions consist of two ψ1-tetrahedral [SeO3]2− subunits (d(Se–Ot) = 164–167 pm, d(Se–Ob) = 176–185 pm, ∢(O–Se–O) = 93–104°) sharing one bridging oxygen atom (Ob) with ∢(Se–Ob–Se) = 121–128°. The vibrational modes of the complex anionic [Se2O5]2− entities were characterized via single-crystal Raman spectroscopy.

On the labyrinthine world of arsenites: a single-crystal neutron and X-ray diffraction study of cafarsite

The crystal chemistry of a cafarsite sample from the fengitic orthogneisses of the Mt. Leone-Arbola nappe (Lower Penninic), forming the central body of Mount Cervandone and cropping out both in Switzerland and Italy (Alpe Devero area, Verbano–Cusio–Ossola province), was investigated by electron microprobe analysis in wavelength-dispersive mode (EPMA-WDS), single-crystal Raman spectroscopy, and single-crystal X-ray and neutron diffraction at 293 K. The sample of cafarsite of this study was found experimentally to be anhydrous and the chemical formula obtained on the basis of the EPMA-WDS data and structural refinements is the following: Ca1,Ca2(Ca15.56Na0.44)Σ16Fe1(Na0.53Fe2+0.17REE0.30)Σ1.00Mn1,Ti,Fe2(Ti7.46Fe3+4.47Fe2+3.20Mn2+0.85Al0.11) Σ16.11As1,As2,As3(AsO3)28 FF, with the general chemical formula Ca16(Na,Fe2+,REE)(Ti, Fe3+,Fe2+,Mn2+,Al)16(AsO3)28F [or Ca16(Na,Fe2+,REE)(Ti,Fe3+,Al)12(Fe2+,Mn)4(AsO3)28F]. Our experimental findings show that fluorine, which was unconsidered in the previous studies, is a key element. The anhydrous nature of this sample is also confirmed by its Raman spectrum, which does not show any evidence of active bands ascribable to the O–H stretching region. The X-ray and neutron structure refinements provide a structure model that is partially in agreement with the previous experimental findings. The space group (i.e. Pn3) and the unit-cell constant [i.e. 15.9507(4) A] are conform to the literature data, but the structure of cafarsite, here refined, contains the following building units: three independent AsO3 groups (trigonal pyramids), one CaO6F polyhedron, one CaO8 polyhedron, two independent (Ti,Fe)O6 octahedra, one (Na,Fe,REE)O8 polyhedron, and one (Mn,Fe)O6 octahedron. Connections among polyhedra are mainly due to edge- or vertex-sharing; the AsO3 groups are not connected to each other.

Closing the Gap: Structural Evidence for the Missing Hexabromide Dianion [Br6 ]2.

The formation and experimental characterization of the first hexabromide dianion is presented. This dianion fills the last remaining gap in the series of polybromides from the tribromide [Br3 ]- to the undecabromide [Br11 ]- . The experimental results are compared to quantum-chemical calculations. These calculations predict-based on electrostatic interactions-a T-structure for the hexabromide dianion, while halogen-halogen bonding favors the hockey-stick-like structure experimentally found in the crystal structure. The hexabromide is built of two tribromide moieties, one of which is highly asymmetric. The classification of this unique anion as hexabromide dianion is discussed. The counter ion [C5 H10 N2 Br]+ stabilizes the hexabromide dianion by additional σ-hole interactions. The compound is fully characterized by mass spectrometry, NMR-, IR and single crystal Raman spectroscopies as well as single-crystal X-ray diffraction.

Two halide-containing cesium manganese vanadates: synthesis, characterization, and magnetic properties.

Two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions. One compound, Cs3Mn(VO3)4Cl, (1) was prepared using a mixed cesium hydroxide/chloride mineralizer, and crystallizes in the polar noncentrosymmetric space group Cmm2, with a = 16.7820(8) Å, b = 8.4765(4) Å, c = 5.7867(3) Å. This structure is built from sinusoidal zig-zag (VO3)n chains that run along the b-axis and are coordinated to Mn2+ containing (MnO4Cl) square-pyramidal units that are linked together to form layers. The cesium cations reside between the layers, but also coordinate to the chloride ion, forming a cesium chloride chain that also propagates along the b-axis. The other compound, Cs2Mn(VO3)3F, (2) crystallizes in space group Pbca with a = 7.4286(2) Å, b = 15.0175(5) Å, c = 19.6957(7) Å, and was prepared using a cesium fluoride mineralizer. The structure is comprised of corner sharing octahedral Mn2+ chains, with trans fluoride ligands acting as bridging units, whose ends are capped by (VO3)n vanadate chains to form slabs. The cesium atoms reside between the manganese vanadate layers, and also play an integral part in the structure, forming a cesium fluoride chain that runs along the b-axis. Both compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and single-crystal Raman spectroscopy. Additionally, the magnetic properties of 2 were investigated. Above 50 K, it displays behavior typical of a low dimensional system with antiferromagnetic interactions, as to be expected for linear chains of manganese(ii) within the crystal structure.

Strontium manganese vanadates from hydrothermal brines: Synthesis and structure of Sr2Mn2(V3O10)(VO4), Sr3Mn(V2O7)2, and Sr2Mn(VO4)2(OH)

Three new strontium manganese vanadates, Sr2Mn2(V3O10)(VO4) (I), Sr3Mn(V2O7)2 (II), and Sr2Mn(VO4)2(OH) (III), were prepared using a high temperature (580°C) hydrothermal method with various chloride salts as the mineralizer. Minor differences in the chloride stoichiometry led to significant differences in product. Compound I crystallizes in the monoclinic space group P21/c (a = 6.8773(12)Å, b = 15.061(3)Å, c = 11.609(2)Å, β = 96.745(8)°), and consists of edge-shared octahedral manganese(II) dimers coordinated by trimeric [V3O10] and monomeric [VO4] groups. Compound II crystallizes in the tetragonal crystal system, P43212 (a = 6.9951(2)Å, c = 25.4390(7)Å), and is built from monomeric manganese(II) octahedra chelated by two pyrovanadate [V2O7] groups and linked to each other by additional pyrovanadates to form layers. Compound III is a noncentrosymmetric variation on the brackebuschite structure type, crystallizing in the monoclinic space group P21 (a = 7.6316(3)Å, b = 6.1204(3)Å, c = 8.6893(3)Å, β = 111.3940(10)°). The structure is composed of octahedral manganese(III) edge-sharing chains coordinated to corner-sharing monomeric [VO4] groups, thereby forming a manganese vanadate chain. All compounds were characterized by single-crystal X-Ray diffraction, powder X-Ray diffraction, infrared spectroscopy and single-crystal Raman spectroscopy. Density functional theory calculations were employed to investigate the relative stability of compound III.

The high-pressure behavior of spherocobaltite (CoCO3): a single crystal Raman spectroscopy and XRD study

Magnesite (MgCO3), calcite (CaCO3), dolomite [(Ca, Mg)CO3], and siderite (FeCO3) are among the best-studied carbonate minerals at high pressures and temperatures. Although they all exhibit the calcite-type structure ( $${\text{R}}\bar{3}{\text{c}}$$ ) at ambient conditions, they display very different behavior at mantle pressures. To broaden the knowledge of the high-pressure crystal chemistry of carbonates, we studied spherocobaltite (CoCO3), which contains Co2+ with cation radius in between those of Ca2+ and Mg2+ in calcite and magnesite, respectively. We synthesized single crystals of pure spherocobaltite and studied them using Raman spectroscopy and X-ray diffraction in diamond anvil cells at pressures to over 55 GPa. Based on single crystal diffraction data, we found that the bulk modulus of spherocobaltite is 128 (2) GPa and K′ = 4.28 (17). CoCO3 is stable in the calcite-type structure up to at least 56 GPa and 1200 K. At 57 GPa and after laser heating above 2000 K, CoCO3 partially decomposes and forms CoO. In comparison to previously studied carbonates, our results suggest that at lower mantle conditions carbonates can be stable in the calcite-type structure if the radius of the incorporated cation(s) is equal or smaller than that of Co2+ (i.e., 0.745 A).

No pyroanions: The representatives of the lanthanoid(III) fluoride oxidodimolybdates(VI) LnFMo2O7 with the Smaller Cations (Ln = Eu – Yb)

The representatives of lanthanoid(III) fluoride oxidodimolybdates(VI) with the formula LnFMo2O7 (Ln = Eu – Yb) occur during reactions of Ln2O3 and LnF3 with MoO3 in 1: 1: 6molar ratio after 6 days in evacuated silica ampoules at 850°C. The title compounds crystallize monoclinically in space group P2/c (a = 421 – 436, b = 651 – 667, c = 1133 – 1140pm and β = 90.4 – 90.6°, Z =2). The crystal structures contain crystallographically unique Ln3+ cations, which are surrounded by two F– and five O2– anions each, forming distorted pentagonal bypramids with the F− anions as apical vertices by which these bipyramids are fused together to strands according to {[LnF2/2vO5/1t]8−}∞1 running parallel to the a axis. The Mo6+ cations show a distorted square-pyramidal coordination environment of five O2− anions. These pyramids are interconnected by common edges and vertices to form chains with the formula {[MoO2/2eO1/2vO2/1t]−}∞1 which are arranged parallel to [001]. Besides the crystal structure determination single crystal Raman spectroscopy was performed and the magnetic behavior of HoFMo2O7 was determined.

Synthesis, crystal structure and Raman spectra of [dabcoH2]CuICl3, [dabcoH2]3Cl4CuIICl4(DMSO) and Cu3Cl3(dabco)(DMSO) (dabco = 1,4-diazabicyclo [2.2.2] octane)

Dissolving elemental copper in a CCl4–DMSO mixture in the presence of dabco (dabco = 1,4-diazabicyclo [2.2.2] octane) resulted in the formation of a compound with the composition [dabcoH2][CuCl3] featuring a univalent copper salt. This compound, composed of discrete dabcoH22+ cations and CuCl32− anions, represents the first example of a copper(I) chloride derivative containing a doubly protonated [dabcoH2]2+ unit, and a very rare example of the oxidative dissolving of copper in a CCl4–DMSO mixture to give a Cu(I) compound. The addition of some drops of water to the initial reaction mixture led to the formation of the [dabcoH2]3Cl4CuCl4(DMSO). Three [dabcoH2]2+ units and four Cl− anions, bound via N–H…Cl hydrogen bonds, form a horseshoe-like cationic fragment. The divalent copper ion possesses a rather unusual pseudo-tetrahedral surrounding. The comproportionation reaction of CuCl2·2H2O and copper powder in the presence of dabco in DMSO results in the formation of the Cu3Cl3(dabco)(DMSO) complex. Copper and chlorine ions form unprecedented Cu6Cl6 cores, interconnected by neutral dabco linkers into infinite 2-D layers. All the compounds were characterized using the single-crystal X-ray diffraction technique and Raman spectroscopy.

Structural, Spectroscopic, and Electrochemical Characterization of Semi-Conducting, Solvated [Pt(NH3)4](TCNQ)2·(DMF)2 and Non-Solvated [Pt(NH3)4](TCNQ)2

The demand for catalysts that are highly active and stable for electron-transfer reactions has been boosted by the discovery that [Pt(NH3)4](TCNQF4)2 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) is an efficient catalyst. In this work, we prepare and characterize the two related [Pt(NH3)4]2+ complexes, [Pt(NH3)4](TCNQ)2·(DMF)2 (1) and [Pt(NH3)4](TCNQ)2 (2). Reaction of [Pt(NH3)4](NO3)2 with LiTCNQ in a mixed solvent (methanol/dimethylformamide, 4 : 1 v/v) gives [Pt(NH3)4](TCNQ)2·(DMF)2 (1), whereas the same reaction in water affords [Pt(NH3)4](TCNQ)2 (2). 2 has been previously reported. Both 1 and 2 have now been characterized by single-crystal X-ray crystallography, Fourier-transform (FT)IR, Raman and UV-vis spectroscopy, and electrochemistry. Structurally, in 1, the TCNQ1− anions form infinite stacks with a separation between adjacent anions within the stack alternating between 3.12 and 3.42 Å. The solvated structure 1 differs from the non-solvated form 2 in that pairs of TCNQ1− anions are clearly displaced from each other. The conductivities of pressed pellets of 1 and 2 are both in the semi-conducting range at room temperature. 2 can be electrochemically synthesized by reduction of a TCNQ-modified electrode in contact with an aqueous solution of [Pt(NH3)4](NO3)2 via a nucleation growth mechanism. Interestingly, we discovered that 1 and 2 are not catalysts for the ferricyanide and thiosulfate reaction. Li+ and tetraalkylammonium salts of TCNQ1−/2− and TCNQF41−/2− were tested for potential catalytic activity towards ferricyanide and thiosulfate. Only TCNQF41−/2− salts were active, suggesting that the dianion redox level needs to be accessible for efficient catalytic activity and explaining why 1 and 2 are not good catalysts. Importantly, the origin of the catalytic activity of the highly active [Pt(NH3)4](TCNQF4)2 catalyst is now understood, enabling other families of catalysts to be developed for important electron-transfer reactions.