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Cluster compounds containing the [(W6I8)(CH3CN)6]4+ ion were established. Photophysical properties of [(W6I8)(CH3CN)6](BF4)4 are compared to those of compounds featuring the [(W6I8)L6]2− ion.

The discovery of melamine by Justus von Liebig was fundamental for the development of several fields of chemistry. The vast majority of compounds with melamine or melamine derivatives appear as adducts. Herein, we focus on the development of novel compounds containing anionic melamine species, namely the melaminates. For this purpose, we analyze the reaction of SbCl3 with melamine by differential scanning calorimetry (DSC). The whole study includes the synthesis and characterization of three antimony compounds that are obtained during the deprotonation process of melamine to melaminate with the reaction sequence from SbCl4(C9N18H19) (1) via (SbCl4(C6N12H13))2 (2) to SbCl(C3N6H4) (3). Compounds are characterized by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), and infrared spectroscopy (IR). The results give an insight into the mechanism of deprotonation of melamine, with the replacement of one, two, or eventually three hydrogen atoms from the three amino groups of melamine. The structure of (3) suggests that metal melaminates are likely to form supramolecular structures or metal-organic frameworks (MOFs).

Y4O2(CN2)3Cl2 and some isotypic rare earth (RE) carbodiimides RE4O2(CN2)3Cl2 (RE = Sm, Gd, Tb) were prepared by solid-state metathesis reaction between RECl3, REOCl and Li2CN2. The crystal structure of Y4O2(CN2)3Cl2 was solved and refined from single-crystal XRD data with the monocline space group C2/m. Homologous compounds with RE = Sm, Gd were assigned isotopically by means of XRD powder diffraction. The structure of Y4O2(CN2)3Cl2 is characterized by one-dimensional cluster chains which are showing a striking resemblance to the trans-edge bridging RE6-octahedra in the structures of Y2Cl3, β-Y2Cl3N, and RE2N(CN2)Cl, despite different numbers of cluster electrons. Crystals of RE4O2(CN2)3Cl2 appear as transparent rods. The presence of (NCN)2− ions is confirmed by infrared spectroscopy. Y4O2(CN2)3Cl2, doped with Ce3+, is a photoluminescent material showing an emission band in the orange region (λem = 550 nm) of the visible spectrum.

New rare earth (RE) carbodiimides having the formula RE8O(CN2)10Br2 were synthesized by solid-state metathesis reactions. Structure determinations and refinements, based on single-crystal X-ray diffraction data, are performed with the space group P͞3c1. Homologous compounds with RE = La, Ce, Pr, and Nd are assigned isotypically. The refined crystal structure appears most unusual for rare earth carbodiimide compounds. The structure is characterized by the formally neutral [RE6O(NCN)8] fragment that is tightly interconnected by carbodiimide ions into a network structure, and contains additional RE3+ ions in the structure. Crystals of the compounds show characteristic colors of their corresponding RE3+ ions and behave stable in air. The presence of (CN2)2− ions was confirmed by infrared spectroscopy. Ce8O(CN2)10Br2 is a photoluminescent material that is showing a broad and efficient emission band in the yellow region of the visible spectrum.

The synthesis of Nb4S3, a previously undiscovered binary sulfide, was achieved using Nb3Br7S as a precursor. Its structure is composed of Nb6S triangular prisms arranged in a polar (Imm2) configuration, with sulfur atoms lying in channels along the a axis. Electrical resistivity measurements and density functional theory calculations were used to determine that Nb4S3 is metallic and therefore a polar metal, with metallic bands occupied by electrons with primarily niobium character. The electrons near the Fermi level are so closely associated with the niobium sublattice that the sulfur atoms have positive Born effective charges, indicating that the electrostatic interactions between sulfur atoms are unscreened. Calculations of the dependence of the electron density on the sulfur atomic positions confirm that the metallic electrons do not screen the dipole-dipole interactions between sulfur atoms, which allows polarity and metallicity to coexist in Nb4S3. These findings suggest that applied electric fields might be able to reverse the polarity of thin films of Nb4S3.

Crystals of Cu3(C3N6H3) are formed by a solid-state reaction of CuCl with melamine to form a layered framework structure with open pores running along the hexagonal axis direction of the P6/mcc structure. The compound contains the hitherto unknown (C3N6H3)3- ion, assigned as melaminate. Bonding interactions within and between Cu-Cu dumbbells, which connect melaminate ions into layers, are analyzed by density functional theory calculations of the electron localization function and directional Young's modulus. Band structure calculations reveal the material to be a semiconductor with a band gap on the order of 2 eV.

Thiourea S-oxides can be viewed as formal analogs of the currently unknown diamino-substituted Criegee intermediates (urea O-oxides). However, the preparation of such S-oxides is rather challenging, and the direct oxidation of thioureas typically only leads to formation of desulfurized products. Employing the accurate revDSD-PBEP86-D4 double hybrid density functional, it was found that the peracid mediated oxidation of thiourea S-oxides exhibits a lower reaction barrier than the oxidation of the corresponding thiourea itself in contrast to most other ordinary thioketones. The undesired overoxidation reactivity, which is associated with strong π-donation from the thiourea's nitrogen atoms, can be partially suppressed by introduction of bulky substituents and the utilization of protic solvents. In this regard, we managed to prepare two sterically encumbered thiourea S-oxides in isolated yields of 35-40 %. The S-oxides are stable in the solid state and in alcoholic solutions at room temperature for extended periods of time, but swiftly decompose in aprotic solvents by disproportionation. A dimesityl-substituted thiourea S-oxide complexed with residual mCBA could be characterized by means of X-ray crystallography, confirming the importance of hydrogen bonding in the stabilization of the amino-substituted C=S

The crystal structures of the hitherto unknown phase W2O3I4 and of WO2I2, a compound that is known to play an important role in the chemical vapor transport of elemental tungsten are reported. We demonstrate that WO2I2 transforms into W2O3I4, and then into WO2 with increasing temperature. Crystals of WO2I2 appear as thin platelets, showing metallic luster; crystals of W2O3I4 appear as black colored needle-shaped platelets. Both compounds adopt layered structures; electronic band structure calculations reveal metallic conductivity for W2O3I4 and surprisingly also for WO2I2.

A modification of TeI4 (ζ-TeI4) was discovered in an attempt to reproduce a reported synthesis of WI4, beginning from WTe2 and iodine. The crystal structure of ζ-TeI4 was solved from single-crystal...

The properties as well as solid‐state structures, singlet fission, and organic field‐effect transistor (OFET) performance of three tetrafluoropentacenes (1,4,8,11: 10, 1,4,9,10: 11, 2,3,9,10: 12) are compared herein. The novel compounds 10 and 11 were synthesized in high purity from the corresponding 6,13‐etheno‐bridged precursors by reaction with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate at elevated temperatures. Although most of the molecular properties of the compounds are similar, their chemical reactivity and crystal structures differ considerably. Isomer 10 undergoes the orbital symmetry forbidden thermal [4+4] dimerization, whereas 11 and 12 are much less reactive. The isomers 11 and 12 crystallize in a herringbone motif, but 10 prefers π–π stacking. Although the energy of the first electric dipole‐allowed optical transition varies only within 370 cm−1 (0.05 eV) for the neutral compounds, this amounts to roughly 1600 cm−1 (0.20 eV) for radical cations and 1300 cm−1 (0.16 eV) for dications. Transient spectroscopy of films of 11 and 12 reveals singlet‐fission time constants (91±11, 73±3 fs, respectively) that are shorter than for pentacene (112±9 fs). OFET devices constructed from 11 and 12 show close to ideal thin‐film transistor (TFT) characteristics with electron mobilities of 2×10−3 and 6×10−2 cm2 V−1 s−1, respectively., Under the influence of fluorine: The (photo‐)physical and chemical properties of tetrafluoropentacene regioisomers are altered considerably in dependence of the substitution pattern. The variation of the fluorination degree and pattern of pentacenes provides a useful model for gaining detailed insight into forces that control crystallization and for studying the structure–property relationships of these organic semiconductors.

Photophysical properties of tungsten iodides with the [W6I14]2− cluster core have been described with respect to phosphorescence and phosphorescence quenching by molecular oxygen. This process involves energy transfer from excited triplet states of the cluster onto molecular oxygen. In the present study we investigate deactivation channels of exited triplet states of the [W6I14]2− cluster towards rare earth ions. For this purpose, we synthesized several supramolecular assemblies made of [W6I14]2− clusters and metal cryptates and investigated their crystal structures and photophysical properties. UV/Vis photoexcitation of solid [Crypt-A]-[W6I14] (A = alkaline metal) and [Crypt-RE]-[W6I14] revealed phosphorescence of the cluster, respectively of the photophysically active rare earth metal (RE) center. A cluster to cryptate energy transfer is proven with a photophysically active rare earth ion by the emission of Yb3+ at 977 nm (2F5/2–2F7/2) and Nd3+ 1072 nm (4F3/2–4I11/2). These results show that an effective excitation of near-infrared-emitting rare earth ions is possible under excitation up to 550 nm with [Crypt-RE]-[W6I14] assemblies.

The successful synthesis and first structural characterization by single crystal X-ray crystallography of a highly strained benzoborirene motif, as well as its reactivity towards selected electrophiles and nucleophiles are reported.

The synthesis of Nb

The formation of the new compound Sn9O5Cl4(CN2)2 is reported and placed in the context of several other recently discovered tin carbodiimide compounds (Sn(CN2), Sn2O(CN2), and Sn4Cl2(CN2)3), all of...

In search of iodine-rich compounds with an octahedral tungsten cluster, we explored the treatment of β-W6I12, the most stable tungsten iodide cluster compound, with liquid iodine. The most iodine-r...

A solid-state metathesis reaction between equimolar amounts of Li2(CN2) and SnCl2 revealed the formation of two new compounds, Sn4Cl2(CN2)3 and Sn(CN2). Thermal analysis of this reaction indicated ...

The phase LixCa16−xSi17N32−xO2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F3m (a = 14.7391(1) A, Z = 4); it is closely related to the previously reported structure of Ca16Si17N34. The structure of LixCa16−xSi17N32−xO2+x is based on a complex network of [SiN4] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu2+ emission at 536 nm on excitation with near-UV or blue radiation at 350–480 nm. Ce3+ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.

Yellow transparent single crystals of the new compound K2Pb(OCN)I3 were synthesized from a mixture of lead iodide and potassium cyanate through a solid-state reaction, which was controlled by the differential scanning calorimetry (DSC) technique. The single crystal X-ray refinement showed that K2Pb(OCN)I3 crystallizes in the cubic system (Fdm, a = 16.295(2) A, V = 4327(1) A3, Z = 16 and R1 = 0.0167). The structure is basically composed of two frameworks built from potassium tetrahedra capped by OCN− units and corner-sharing lead iodide octahedra. The infrared spectrum of K2Pb(OCN)I3 reveals the presence of vibration modes that were assigned to cyanate ions. The band structure and total and partial density of states calculated by DFT with the PBE functional (CASTEP code) showed that this compound exhibits a direct band gap of 2.19 eV, which is in good agreement with the experimental value obtained from a diffuse reflectance measurement (2.4 eV). The investigation of the electrical properties of this material demonstrates that it is highly resistive and has large permittivity (relative values of up to 104 at 150 °C). However, it does not display ferroelectric behavior.

The crystal structures of the hitherto unknown phase W2O3I4 and of WO2I2, a compound that is known to play an important role in the chemical vapor transport of elemental tungsten are reported. We demonstrate that WO2I2 transforms into W2O3I4, and then into WO2 with increasing temperature. Crystals of WO2I2 appear as thin platelets, showing metallic luster; crystals of W2O3I4 appear as black colored needle-shaped platelets. Both compounds adopt layered structures; electronic band structure calculations reveal metallic conductivity for W2O3I4 and surprisingly also for WO2I2.

A series of new compounds MI(OCN) were prepared from the mixtures of MI2 and K(OCN) (M = Sr, Eu or Ba) by solid-state reactions that were controlled by differential scanning calorimetry (DSC) and differential thermal analysis (DTA) techniques. The presence of two phases is highlighted for BaI(OCN) which crystallizes in the Pnma (α-BaI(OCN)) and Cmcm (β-BaI(OCN)) space groups. The SrI(OCN), EuI(OCN) and β-BaI(OCN) compounds crystallize in the same orthorhombic Cmcm space group and the structure consists of a layered arrangement of [M2I2]2+ blocks separated by single layers of cyanate ions that are found to be related to the Sillen-type structure. The polymorphism of BaI(OCN) was also observed by analyzing the infrared (IR) spectra. This analysis showed for β-BaI(OCN) splitting bands, which were ascribed to the presence of more than one resonant cyanate form that can be induced by the dynamical disorder of OCN units. In contrast, the α-BaI(OCN) vibration modes suppose the existence of one cyanate form that adopts a defined orientation. The SrI(OCN) and BaI(OCN) compounds were doped with Eu2+. The luminescence spectra recorded under excitation at 340 and 350 nm revealed a blue emission of Eu2+ at 431 nm for the β-BaI(OCN) and SrI(OCN) phases and at 427 nm for the α-BaI(OCN) phase that was ascribed to the 4f65d1→8S7/2 (4f7) transition.

Photophysical properties of tungsten iodides with the [W6I14]2- cluster core have been described with respect to phosphorescence and phosphorescence quenching by molecular oxygen. This process involves energy transfer from excited triplet states of the cluster onto molecular oxygen. In the present study we investigate deactivation channels of exited triplet states of the [W6I14]2- cluster towards rare earth ions. For this purpose, we synthesized several supramolecular assemblies made of [W6I14]2- clusters and metal cryptates and investigated their crystal structures and photophysical properties. UV/Vis photoexcitation of solid [Crypt-A]-[W6I14] (A = alkaline metal) and [Crypt-RE]-[W6I14] revealed phosphorescence of the cluster, respectively of the photophysically active rare earth metal (RE) center. A cluster to cryptate energy transfer is proven with a photophysically active rare earth ion by the emission of Yb3+ at 977 nm (2F5/2-2F7/2) and Nd3+ 1072 nm (4F3/2-4I11/2). These results show that an effective excitation of near-infrared-emitting rare earth ions is possible under excitation up to 550 nm with [Crypt-RE]-[W6I14] assemblies.

The new compound WTe2I was prepared by a reaction of WTe2 with iodine in a fused silica ampule at temperatures between 40 and 200 °C. Iodine atoms are intercalated into the van der Waals gap between tungsten ditelluride layers. As a result, the WTe2 layer separation is significantly increased. Iodine atoms form planar layers between each tungsten ditelluride layer. Due to oxidation by iodine the semimetallic nature of WTe2 is changed, as shown by comparative band structure calculations for WTe2 and WTe2I based on density functional theory. The calculated phonon band structure of WTe2I indicates the presence of phonon instabilities related to charge density waves, leading to an observed incommensurate modulation of the iodine position within the layers.

Ag2[W6I14] and A2–x[W6I14] compounds with A = Na, Li were prepared from binary tungsten iodides (W3I12) and corresponding metal iodides. Their crystal structures are analyzed on the basis of X-ray ...

Tungsten iodide compounds feature a surprising diversity of binary compounds. Their formation conditions and phase equilibria depend very much on the surrounding iodine partial pressure and temperature. Herein we focus on square-pyramidal tungsten iodide cluster compounds with their iodine loss, structural rearrangements, cross-linking behavior, and final transformation into the octahedral cluster compound β-W6I12 at elevated temperatures. Reactions depart from W5I16 at different iodine pressures and temperatures. The thermal decomposition of W5I16 at low iodine pressure passes through a number of cluster compounds (W5I15, W5I13·xI2, β-W5I12, and W5I11) under release of iodine. At higher iodine pressures, only one intermediate compound (α-W5I12) was found. Thermal decomposition of W5I16 was examined by differential thermal/thermogravimetric analysis, differential scanning calorimetry, and X-ray diffraction (XRD) measurements. New compounds (W5I15, W5I13·xI2, and W5I11) were structurally characterized by means of XRD techniques. The crystal structure of W5I11 reveals a nice relationship to its transformation product W6I12.

Compounds Mg3Al3N5, Mg3Al2N4 and Mg3AlN3 were successfully synthesized at 1100 °C in a closed system utilizing weld shut niobium ampoules. Their crystal structures were solved and refined on the basis of powder X-ray diffraction data with the space group P63/mmc (a = b = 3.2422(1), c = 26.340(1), Z = 2) for Mg3Al3N5, P"3" m1 (a = b = 3.2860(1), c = 10.7461(1), Z = 1) for Mg3Al2N4 and R"3" m (a = b = 3.3683(0), c = 25.4835(1), Z = 1) for Mg3AlN3. Their crystal structures are characterized by wurtzite-type [AlN] and [MgN] block layers alternating with NiAs-type related [MgN] layers along the c-axis direction. Europium(III)-doped samples of Mg3Al3N5 show characteristic emission in the visible region of the spectrum, on excitation with UV radiation at λex = 370 nm. Mg3AlN3 doped with europium(II) shows yellow luminescence on excitation with UV radiation at λex = 365 nm.

A reaction cycle is shown for octahedral tungsten iodide compounds. The thermal transformation of W6I16 (W6I12·2I2) via release of iodine proceeds via the new W6I13 (W6I12·xI2 with 0 < x ≤ 1/2) to yield a new modification of W6I12, denoted as α-W6I12. When heated, α-W6I12 is converted into the known (β-)W6I12. The reaction of (β-)W6I12 with I2 leads to the formation of the starting compound W6I16. The new compounds W6I13 (W6I12·xI2 with 0 < x ≤ 1/2) and α-W6I12 are structurally characterized by powder and single-crystal X-ray diffraction techniques. The thermal decomposition of W6I16 and the monotropic phase transition of α-W6I12 into β-W6I12 are examined by differential scanning calorimetry measurements.

The formation of the new compound Sn

In search of iodine-rich compounds with an octahedral tungsten cluster, we explored the treatment of β-W

The phase Li

The photophysics of selected tungsten iodide clusters was examined with respect to their role as a photosensitizer for the production of singlet oxygen, O 2 (a 1 Δ g ). We examined all-iodo octahedral clusters, [W 6 I 8 (I 6 )] 2- , and ligand-substituted octahedral clusters, [W 6 I 8 (L 6 )] 2- , in which the ligand, L, occupies the outer apical positions surrounding the cluster core. We also examined a square-pyramidal cluster, [W 5 I 8 (I 5 )] ? , in which the tungsten core was presumably more accessible to diffusional encounter with ground state oxygen, O 2 (X 3 Σ g - ). For the compounds examined, we find pronounced cluster-dependent changes in the yield of photosensitized O 2 (a 1 Δ g ) production. In particular, although the iodine-encased octahedral cluster, [W 6 I 8 (I 6 )] 2- , is an efficient O 2 (a 1 Δ g ) sensitizer, the pyramidal cluster, [W 5 I 8 (I 5 )] ? , does not make O 2 (a 1 Δ g ) at all. The latter provides fundamental insight into the important case where the sensitizer triplet state is nearly degenerate with the O 2 (X 3 Σ g - )-O 2 (a 1 Δ g ) transition energy at 1 eV. Our data indicate that even with near resonance, energy transfer to form O 2 (a 1 Δ g ) will not occur within the 3 sensitizer-O 2 (X 3 Σ g - ) encounter pair if other more efficient channels for energy dissipation are available.

The heteroleptic cluster compound (W6I8)Cl4 was prepared by thermal conversion of the homoleptic clusters W6I12 and W6Cl12 at 700 °C to yield a bright yellow powder. The presence of the smaller chlorido ligands in apical positions of [(W6I8)Cl6]2– creates nearly spherically clusters showing thermal and chemical inertness. Photoluminescence studies revealed a strong red phosphorescence from excited spin-triplet states.