Electronic structure and transport in the potential Luttinger liquids CsNb3Br7S and RbNb3Br7S.

The crystal structures of ANb3Br7S (A = Rb and Cs) have been refined by single crystal X-ray diffraction, and are found to form highly anisotropic materials based on chains of the triangular Nb3 cluster core. The Nb3 cluster core contains seven valence electrons, six of them being assigned to Nb-Nb bonds within the Nb3 triangle and one unpaired d electron. The presence of this surplus electron gives rise to the formation of correlated electronic states. The connectivity in the structures is represented by one-dimensional [Nb3Br7S]- chains, containing a sulphur atom capping one face (µ3) of the triangular niobium cluster, which is believed to induce an important electronic feature. Several types of studies are undertaken to obtain deeper insight into the understanding of this unusual material: the crystal structure, morphology and elastic properties are analysed, as well the (photo-)electrical properties and NMR relaxation. Electronic structure (DFT) calculations are performed in order to understand the electronic structure and transport in these compounds, and, based on the experimental and theoretical results, we propose that the electronic interactions along the Nb chains are sufficiently one-dimensional to give rise to Luttinger liquid (rather than Fermi liquid) behaviour of the metallic electrons.

Tungsten Iodide Clusters as Singlet Oxygen Photosensitizers: Exploring the Domain of Resonant Energy Transfer at 1 eV.

The photophysics of selected tungsten iodide clusters was examined with respect to their role as a photosensitizer for the production of singlet oxygen, O2(a1Δg). We examined all-iodo octahedral clusters, [W6I8(I6)]2-, and ligand-substituted octahedral clusters, [W6I8(L6)]2-, in which the ligand, L, occupies the outer apical positions surrounding the cluster core. We also examined a square-pyramidal cluster, [W5I8(I5)]-, in which the tungsten core was presumably more accessible to diffusional encounter with ground state oxygen, O2(X3Σg-). For the compounds examined, we find pronounced cluster-dependent changes in the yield of photosensitized O2(a1Δg) production. In particular, although the iodine-encased octahedral cluster, [W6I8(I6)]2-, is an efficient O2(a1Δg) sensitizer, the pyramidal cluster, [W5I8(I5)]-, does not make O2(a1Δg) at all. The latter provides fundamental insight into the important case where the sensitizer triplet state is nearly degenerate with the O2(X3Σg-)-O2(a1Δg) transition energy at 1 eV. Our data indicate that even with near resonance, energy transfer to form O2(a1Δg) will not occur within the 3sensitizer-O2(X3Σg-) encounter pair if other more efficient channels for energy dissipation are available.

Facile Way of Synthesis for Molybdenum Iodides.

Molybdenum iodides are prepared based on a new way of synthesis, namely, via reductive metathesis reaction of MoCl5 with SiI4. MoI3 was formed at 150 °C. Mo6I12 and the new molybdenum iodides Mo6I16 and Mo6I18 with the well-known [Mo6I8]4+ cluster core were obtained in the temperature range 550-600 °C. Compounds were structurally characterized by powder and single-crystal X-ray diffraction techniques.

A Facile Method for the Synthesis of Binary Tungsten Iodides.

The preparation of tungsten iodides in large quantities is a challenge because these compounds are not accessible using an easy synthesis method. A new, remarkably efficient route is based on a halide exchange reaction between WCl6 and SiI4. The reaction proceeds at moderate temperatures in a closed glass vessel. The new compounds W3I12 (W3I8 ⋅2 I2) and W3I9 (W3I8 ⋅½I2) containing the novel [W3I8] cluster are formed at 120 and 150 °C, and remain stable in air. W3I12 is an excellent starting material for the synthesis of other metal-rich tungsten iodides. At increasing temperature these trinuclear clusters undergo self-reduction until an octahedral tungsten cluster is formed in W6I12 . The synthesis, structure, and an analysis of the bonding of compounds containing this new trinuclear tungsten cluster are presented.

Synthesis and SHG properties of two new cyanurates: Sr3(O3C3N3)2 (SCY) and Eu3(O3C3N3)2 (ECY).

The new cyanurates Sr3(O3C3N3)2 (SCY) and Eu3(O3C3N3)2 (ECY) were prepared via exothermic solid state metathesis reactions from MCl2 (M = Sr, Eu) and K(OCN) in silica tubes at 525 °C. Both structures were characterized by means of powder and single crystal X-ray diffraction, and their structures are shown to crystallize with the noncentrosymmetric space group R3c (No. 161). Infrared spectra and nonlinear optical properties (NLO) of SCY and ECY are reported in comparison to those of CCY and ß-BaB2O4 (ß-BBO).

Synthesis, structure, and frequency-doubling effect of calcium cyanurate.

Calcium cyanurate is synthesized by reacting calcium chloride with potassium cyanate following a solid-state reaction. The formation of the new compound Ca3(O3C3N3)2 (CCY), which occurs by the cyclotrimerization of cyanate ions, was examined thermoanalytically and the crystal structure was determined by single-crystal structure analysis. The structure of CCY is closely related to the structure of the well-known oxoborate ß-BaB2O4 (BBO). Second harmonic generation (SHG) measurements on crystal powders show a higher SHG efficiency for CCY than for BBO by about one order of magnitude.

Thermal deprotonation and condensation of melamine in the presence of indium(III)chloride.

The thermal condensation of melamine into molecules melam, melem, and the one-dimensional polymer melon has already been reported. An interesting question arises about the impact of other compounds being present in this process of thermal conversion. The solid-state reaction of C3N6H6 with InCl3 leads to a novel compound featuring deprotonated melam units in a supramolecular assembly, based on the [C12N20H8]4- anion that is interconnected in the structure via N-In-N bonding. The reaction pathway of the formation of this compound is investigated by thermal analysis and the crystal structure of unique (NH4)[(InCl2)3(C12N20H8)]·â…”[InCl3(NH3)] is reported as well as its photoluminescence properties.

The luminescent semiconductor Pb7I6(CN2)4.

The development of new compounds in the domain of metal dinitridocarbonates is most efficiently performed via solid-state metathesis or simply by addition reactions. Our discovery of Pb7I6(CN2)4 is the result of a solid-state reaction of PbCN2 with PbI2 at 420 °C. Its crystal structure was solved and refined from X-ray diffraction data based on a single crystal with the space group P63/mmc. The crystal structure is based on a network of lead tetrahedra, lead trigonal bipyramids and lead octahedra interconnected by [NCN]2- and iodide. Properties of the material were investigated by diffuse reflection measurement, photoluminescence measurements, and electronic band structure calculations demonstrating that this material is a semiconductor.

Solid state complex chemistry: formation, structure, and properties of homoleptic tetracyanamidogermanates RbRE[Ge(CN2)4] (RE = La, Pr, Nd, Gd).

Tetracyanamidometallates with the general formula RbRE[T(CN2)4] (RE = La, Pr, Nd, Gd; T = Si, Ge) were prepared by solid state metathesis reactions starting from stoichiometric mixtures of RECl3, A2[TF6], and Li2(CN2). Reactions were studied by differential thermal analysis that showed ignition temperatures between 360 and 390 °C for the formation of RbGd[T(CN2)4] with T = Si and Ge. The powder diffraction patterns of RbRE[Ge(CN2)4] were indexed isotypically to the already known RbRE[Si(CN2)4] compound. IR spectra of RbLa[Ge(CN2)4] were measured and compared with those of RbLa[Si(CN2)4]. (73)Ge, (87)Rb, and (139)La solid state NMR measurements and density functional theory calculations were used to verify the novel homoleptic [Ge(CN2)4](4-) ion. Luminescence properties of Eu(3+), Ce(3+), and Tb(3+) doped samples are reported.

LaSr3F5(CN2)2: a prototype structure for mixed-valent Eu4F5(CN2)2.

The new compound LaSr(3)F(5)(CN(2))(2) was prepared and structurally characterized as a prototype structure for the remarkably distorted mixed-valent compound Eu(4)F(5)(CN(2))(2), which contains four distinct europium ions in the structure: one Eu(3+) and three Eu(2+). Instead of repeating the given distorted structural pattern, LaSr(3)F(5)(CN(2))(2) forms a structure which can be considered as an ideal high-symmetry structure for Eu(4)F(5)(CN(2))(2), due to the occupation of La(3+) and Sr(2+) ions on one and the same crystallographic position. The crystal symmetry of this structure is an interesting issue to compare with what has been previously proposed.

Refined crystal structure and idealized structure of mixed-valent Eu4F5(CN2)2: transition possible.

The new europium fluoride carbodiimide Eu(4)F(5)(CN(2))(2) was synthesized by solid state reaction from mixtures of EuF(3) and Li(2)(CN(2)) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P ̅42(1)c, no. 114, a = 16.053(1) Å, c = 6.5150(6) Å, Z = 8) reveals three crystallographically distinct [N═C═N](2-) ions in the structure of mixed-valent Eu(4)F(5)(CN(2))(2). The presence of one Eu(3+) and three Eu(2+) per formula unit Eu(4)F(5)(CN(2))(2) is confirmed by magnetic measurements and (151)Eu-Mössbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN](2-) ions in the structure of Eu(4)F(5)(CN(2))(2) follow the motif formed by atoms in the CuAl(2)-type structure. A possible high-symmetry structure of Eu(4)F(5)(CN(2))(2) is discussed on the basis of a group-subgroup scheme.

The trigonal prismatic cluster compound W6CCl15 and a carambolage of tungsten clusters in the structure of the heteroleptic cluster compound W30C2(Cl,Br)68.

Reactions between W(6)Cl(12) and carbon halides can initiate a cascade of reactions and reaction products, yielding W(6)Cl(18), W(6)CCl(18), and W(6)CCl(15) with increasing temperature, before decomposition into tungsten carbide is obtained. The new compound W(6)CCl(15) and the new heteroleptic compound W(30)C(2)(Cl,Br)(68) obtained from these reactions were structurally characterized. The structure of W(30)C(2)X(68) combines a carambolage of two distinct octahedral and one centered trigonal prismatic cluster in one structure as refined by X-ray single-crystal diffraction (P1, Z = 1; a = 12.003(2) A, b = 14.862(3) A, c = 15.792(3) A, alpha = 88.75(2) degrees, beta = 68.85(2) degrees, gamma = 71.19(2) degrees). The unit cell content W(30)C(2)X(68) accommodates five hexanuclear tungsten clusters, similar by a total of three octahedral [W(6)X(8)] type clusters and two carbon-centered trigonal prismatic [W(6)CX(12)] type clusters, sharing terminal halogen atoms to form a network structure. The trigonal prismatic cluster compound W(6)CCl(15) (P2(1)/c, Z = 4; a = 9.8830(4) A, b = 11.8945(4) A, c = 17.8670(7) A, beta = 107.883(2) degrees) is related to the already known compound W(6)CCl(16). According to X-ray powder structure refinement, the structure is showing a special connectivity pattern with short intercluster W-W contacts between trigonal prismatic cluster units.

Synthesis and properties of tetracyanamidosilicates ARE[Si(CN2)4].

Tetracyanamidosilicates of the type ARE[Si(CN(2))(4)] with A = K, Rb, and Cs and RE = Y and La-Lu have been prepared by a solid-state metathesis reaction. The potassium compounds with RE = La-Gd crystallize orthorhombically in the space group P2(1)2(1)2. Rubidium as well as cesium compounds crystallize tetragonally in the space group I4. The luminescent properties of ARE[Si(CN(2))(4)]:Ln compounds with RE = Y, La, and Gd doped with 5 mol % Ln = Ce, Eu, or Tb were investigated. Temperature-dependent magnetic susceptibilities were measured for KGd[Si(CN(2))(4)]. The value of the magnetic moment is 7.3 mu(B)/Gd(3+) ion, which is in line with the expected value for the [Xe]4f(7) configuration of Gd(3+).

Compounds with the electron-rich [W6Cl18]2- cluster anion.

Cluster compounds of the general formula A(2)[W(6)Cl(18)] containing singly charged A cations (A = K, Rb, Ag, Tl, NH(4), N(C(2)H(5))(4), N(n-C(3)N(7))(4), N(n-C(4)H(9))(4)) and [W(6)Cl(18)](2-) anions have been synthesized. Compounds were obtained by W(6)Cl(18) reduction using methanol and the corresponding metal or (alkyl-)ammonium salts. The use of CoCp(2) as reducing agent in inert solvents such as tetrahydrofurane also leads to the ionic compound (Co(C(5)H(5))(2))(2)[W(6)Cl(18)]. All compounds described here evidence the existence of octahedral clusters of the M(6)X(12) type with 20 cluster electrons occupying metal centered states, thus exceeding the conventional number of 16 electrons for this cluster type. Electrospray ionization (ESI) mass spectra were recorded for the neutral compound W(6)Cl(18) and for the ionic salts K(2)[W(6)Cl(18)], Cs(2)[W(6)Cl(18)], and (Co(C(5)H(5))(2))(2)[W(6)Cl(18)], showing that the cluster W(6)Cl(18) unit in these compounds is preserved in solution. The base peak in the ESI spectra for all compounds corresponds to the [W(6)Cl(18)](2-) anion, so that neutral W(6)Cl(18) is prone to undergo a two electron reduction process. This result is confirmed by cyclic voltammetry experiments, which makes of W(6)Cl(18) a very clean mild oxidizing agent. The preparation of the complete series of ionic A(2)[W(6)Cl(18)] (A = K, Cs, CoCp(2)) clusters allows to systematically investigate their structural trends as function of the distinctive cations, which is the main focus of the present work.

Crystal structures, phase-transition, and photoluminescence of rare earth carbodiimides.

Rare earth carbodiimides with the general formula RE 2(CN 2) 3 crystallize with two modifications. A monoclinic( C2/m) modification is obtained for RE = Y, Ce-Tm and a rhombohedral ( R3 c) modification for RE = Tm-Lu. The space group R3 c is confirmed by single-crystal structure determination on Lu 2(CN 2) 3 and indexed powder patterns of RE = Tm, Yb and Lu. The use of diverse chemical syntheses conditions for Tm 2(CN 2) 3 revealed the dimorphic character of this compound. In addition, pressure experiments on Tm 2(CN 2) 3 have induced a phase-transition from rhombohedral to monoclinic. This transformation comprises an increase of the coordination number of Tm from 6 to 7, and a unit-cell volume reduction in the order of 20 %. The photoluminescence behavior of lanthanide doped Gd 2(CN 2) 3:Ln samples is presented with different activators (Ln = Ce, Tb) revealing a broad band emission of Gd 2(CN 2) 3:Ce, quite similar to that of the well-known YAG:Ce.

Up-conversion white emission and other luminescence properties of a YAG:Yb2O3·Tm2O3·Ho2O3@SiO2 glass-nanocomposite.

We report on a glass-nanocomposite material consisting of yttrium aluminum garnet (Y3Al5O12, YAG) nanocrystals co-doped with Yb3+, Tm3+ and Ho3+ ions as well as entrapped into a SiO2 xerogel. This 94YAG·5Yb2O3·0.8Tm2O3·0.2Ho2O3@SiO2 (abbr. YAG:YbTmHo@SiO2) nanocomposite material has been prepared by sol-gel procedure. Its structure and morphology has been characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques as well as energy dispersive X-ray (EDX), X-ray photoelectron (XPS) and luminescence spectroscopies. The luminescent glass-nanocomposite exhibited an up-conversion effect under λ exc = 980 nm and emission when excited under 355 nm in steady-state conditions. Then time-resolved luminescence emission was observed, when the sample was excited at 290 and 355 nm by a pulse laser. Average decay times for the SiO2 matrix and for some transitions of the Tm3+ and Ho3+ dopants present in the YAG:YbTmHo@SiO2 material have been evaluated. The luminescent nanocomposite when excited under 290 or 355 nm wavelengths in both conditions emits blue light. However, the nanocomposite is promising as a single-source white-light phosphor owing to its up-conversion luminescence under 980 nm excitation. Such optical features make the studied material an alternative phosphor.

A journey through ternary lead chlorido tungstates by thermal scanning.

The reduction of tungsten hexachloride with lead powder was investigated by differential scanning calorimetry (DSC) combined with X-ray diffraction (XRD) studies. Intermediate compounds along the way of the reduction of W6+ to W2+ were detected, prepared by solid-state synthesis, and structurally characterized by X-ray diffraction techniques. Five new compounds, namely Pb0.5WCl6, PbW2Cl10, Pb1.5[W3Cl13], Pb2Cl[W3Cl13], and Pb[W6Cl14] are discovered to be formed with increasing temperature, and structurally characterized within this study. The analysis of the reduction pathway is meant to gain a better understanding of the metallothermic reduction process and intercalation chemistry in the solid state.

A ligand substituted tungsten iodide cluster: luminescence vs. singlet oxygen production.

Octahedral tungsten iodide clusters equipped with apical ligands (L) are synthesized to implement substantial photophysical properties. The [W6I8(CF3COO)6]2- cluster reported herein is the first example of a family of ligand substituted [W6I8L6]2- clusters. Such compounds are expected to exhibit a rich photochemistry in which the apical ligands play a crucial role. The versatile solid state and solution phase photophysical properties of (TBA)2[W6I8(CF3COO)6] described herein parallel characteristics obtained in some photophysically active organic compounds, including a broad absorption in the UV/VIS region. Upon irradiation of this compound, a broad red emission is observed in the VIS/NIR region resulting from excited triplet states, and singlet oxygen (a1Δg) is generated in the presence of O2.

Nitridoborates of the lanthanides: synthesis, structure principles, and properties of a new class of compounds.

Investigations of the nitridoborates of lanthanides (Ln) have progressed significantly during the last few years. New compounds have been synthesized and characterized and are presented here together with some of their properties. Currently two distinct methods serve for the preparation of nitridoborate compounds; either hexagonal boron nitride undergoes a fragmentation through the reaction with LnN, or dinitridoborate ions are converted into other nitridoborate ions. Lanthanide nitridoborates contain molecular anions such as [BN]n-, [BN2]3-, [B2N4]8-, [B3N6]9-, and [BN3]6- which may occur in combinations with other nitridoborates or with additional nitride ions. In crystal structures of lanthanide nitridoborates these anions are arranged in layers and are surrounded by metal atoms in a characteristic fashion. Terminal N atoms are capped by metal atoms forming a square-pyramid, and B atoms prefer a trigonal-prismatic environment of metal atoms. Nitridoborates form saltlike as well as metal-rich compounds and have the potential to show a lot of what are considered to be important solid-state properties, thus they have a good chance to establish their position within the group of relevant materials.

Novel hybrid hetero-sandwich architectures via stoichiometric control of host-guest self-organization.

Thiocyanate cadmium and methylviologen hybrid host-guest compounds give two novel multiple sandwich architectures with regular or irregular grids of the anionic layer in the structures as effected by the molar ratios of starting ingredients, and show evidence of charge-transfer to the organic dications.