From 1D to 3D: Perovskites within the System HSC(NH2)2I/CH3NH3I/PbI2 with Maintenance of the Cubic Closest Packing.

This work describes crystalline phases of the system [HSC(NH2)2]I/(CH3NH3)I/PbI2 and discusses the crystal structures in the context of a common cubic closest packing of organic cations and iodide anions with Pb2+ in all anionic octahedral voids. Ternary boundary phases were (CH3NH3)PbI3 (3D perovskite), [HSC(NH2)2]3PbI5 (1D perovskite), [HSC(NH2)2]PbI3 (NH4CdCl3 type), and [HSC(NH2)2]Pb2I5, with strands of edge-sharing octahedra of the NH4CdCl3 type, which are connected to 2D layers via common corners. Within the system, we identified ribbonlike structures of the general composition [HSC(NH2)2]m+1(CH3NH3)mPbmI4m+1 with m = 2 and 3, representing the transition from 1D to 2D structures. Layered structures with variable thickness were found for the series [HSC(NH2)2](CH3NH3)nPbnI3n+1 with n = 1-3. The color and band gap correlate directly with the pattern of how the PbI6 octahedra are linked. 1D structures are colorless or pale yellow to orange. Layered structures are red to black, depending on the layer thickness. A first laboratory-scale solar cell yielded an efficiency of ∼6% based on the compound with n = 3.

First-principles calculation of 11B solid-state NMR parameters of boron-rich compounds II: the orthorhombic phases MgB7 and MgB12C2 and the boron modification γ-B28.

Based on the work on referencing 11B nuclear magnetic resonance (NMR) spectra for molecular icosahedral boranes and the subsequent transfer to the rhombohedral boron-rich borides of the α-rB12 type, we show that the magic angle spinning (MAS) NMR spectra of boron-rich borides with four or five symmetry-independent boron atoms can also be calculated. The calculations are performed on the level of density functional theory (DFT) using the gauge-including projector-augmented wave (GIPAW) approach. As model compounds o-MgB12C2 and MgB7 are used, for which the experimental spectra could be calculated in excellent agreement with a deviation of 1 to 2 ppm. Based on the calculations, the different B atoms can be assigned to the respective signals, taking into account the quadrupolar coupling constants Cq from computation of the electric field gradient (EFG) with its main axis Vzz. It is shown that due to the specific geometric conditions of icosahedra, the magnitudes of Vzz for the boron atoms involved in exohedral B-B bonds to neighbouring icosahedra depend only on the valence electron density of the bond critical point and the distance. This also applies to the bonds to the interstitial B2 unit in MgB7, but not to bonds to the heteroatom of the C2 dumbbell in o-MgB12C2. Both results are in line with our previous observations for the rhombohedral species (α-rB12; B12X2 with X = P, As, O). Finally, the spectrum of γ-B28 was calculated, whose structure also contains B12 icosahedra and interstitial B2 dumbbells. Here, a very similar bonding situation is found for the icosahedron, but the calculations show that the situation for the B2 unit is clearly different. In general, the only parameter that needs to be varied to fit calculated and measured spectra is the linewidth, as this cannot be calculated. For the cases of o-MgB12C2 and MgB7 signal areas are related to corresponding site multiplicities. A prerequisite for the successful application of the chosen method seems to be the presence of a semiconductor with a sufficiently large band gap, which is the case for the compounds investigated.

First-principles calculation of 11B solid-state NMR parameters of boron-rich compounds I: the rhombohedral boron modifications and B12X2 (X = P, As, O).

In the present study, solid-state nuclear magnetic resonance (NMR) spectra under magic angle spinning conditions of the rhombohedral structures α-B and B12P2 are reported together with the corresponding parameter sets from first principles calculations on α-B B12X2 (X = P, As, O). With the combination of density functional theory (DFT) and the gauge-including projector-augmented wave (GIPAW) approach as the theoretical tools at hand the computed 11B parameters lead to unambiguous explanation of the measurements. Thereby, we overcome common obstacles of processing recorded NMR spectra of solid-state compounds with several crystallographic positions, in particular non-trivial signal assignments and parameter determination due to peak overlap or even unexpected intensity/area ratios. In fact, we find very good agreement between the theoretical results and measured spectra without applying fitting procedures. Using the Perdew-Burke-Ernzerhof (PBE) functional, the results of the common construction types for pseudopotentials and referencing methods for the chemical shift determination are compared. Suggestions and conclusions from experimental 11B NMR studies on parameters according to the icosahedral positions are critically discussed, for instance the early suspected correlation to chemical shifts is not confirmed. Regarding the electric field gradient (EFG) a detailed explanation for obtaining small deviations amongst all investigated structures of the icosahedral polar sites compared to the equatorial sites is given. Our results show an important link between the exohedral bonding situation of compounds with icosahedral structure elements and the main axis of the EFG and therefore, also measurable quadrupole coupling constants if certain geometrical conditions are fulfilled. Finally, this work also contributes to establishing the number of unique sites measured by solid-state NMR methods within the modification of ß-B.

Borosulfates-Synthesis and Structural Chemistry of Silicate Analogue Compounds.

Borosulfates are oxoanionic compounds consisting of condensed sulfur- and boron-centered tetrahedra. Hitherto, they were mostly achieved from solvothermal syntheses in SO3 -enriched sulfuric acid, or from reactions with the superacid H[B(HSO4 )4 ]. The crystal structures are very similar to those of the corresponding class of silicates and their substitution variants, especially regarding the typical structural motif of corner-sharing tetrahedra. However, the borosulfates are supposed to be even more versatile, because (BO3 ) units might also be part of the anionic network. The following article deals with detailed reports on the different synthesis strategies, the crystal chemistry of borosulfates in comparison to silicates, and their hitherto identified properties.

GIAO versus GIPAW: Comparison of Methods To Calculate 11B NMR Shifts of Icosahedral Closo-Heteroboranes toward Boron-Rich Borides.

In this work, we perform first-principle density functional theory calculations with the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional to compare the results of the gauge-including atomic orbital (GIAO) method with the gauge-including projector-augmented wave (GIPAW) approach for isotropic 11B nuclear magnetic resonance shifts. GIPAW had been used successfully for the theoretical calculation of nuclear magnetic parameters of 11B species in strong ionic solid-phase compounds such as borates but had been applied very rarely to structures where boron is mainly involved in complex covalent bonding situations, for example, in icosahedra of boron-rich borides. Thus, we investigate the accuracy of both well-known methods and reliability of the effective treatment of core electrons on a test set containing 16 experimentally known closo-(hetero)dodecaboranes. In general, we find very good agreement between GIAO and GIPAW when compared to experimental observations. However, accidental degeneracies of the shift values are better predicted by GIPAW. The optimized molecular geometries on the PBE level agree well with gaseous electron diffraction data and lead to theoretical isotropic chemical 11B shifts with root-mean-square errors of 2.1 and 1.0 ppm depending on the used model of converting absolute shieldings to chemical shifts. The comparison with results from hybrid functionals (B3LYP, B3LYP-D2, and PBE0) shows a minor improvement in accuracy, which is in agreement with 13C shifts of sp3-hybridized species. In order to prove the reliability of the conversion parameters obtained by PBE, we report the calculated 11B shifts of 1,2-, 1,7-, and 1,12-PCB10H11 with GIAO and GIPAW to our knowledge for the first time. Additionally, Bader's analysis is carried out on the converged electron density for all boron species within the molecular test set, yielding no simple direct relation between charge and isotropic shifts.

Oxidative Fluorination of Cu/ZnO Methanol Catalysts.

The influence of a mild difluorine treatment on Cu/ZnO precatalysts for methanol synthesis was investigated. It led to the incorporation of 1.2…1.3±0.1 wt % fluoride into the material. Fluorination considerably increased the amount of ZnOx related defect sites on the catalysts and significantly increased the space-time yields. Although the apparent activation energy EA,app for methanol formation from CO2 and H2 was almost unchanged, the EA,app for the reverse water-gas shift (rWGS) reaction increased considerably. Overall, fluorination led to a significant gain in methanol selectivity and productivity. Apparently, also the quantity of active sites increased.

Tailoring the Band Gap in 3D Hybrid Perovskites by Substitution of the Organic Cations: (CH3 NH3 )1-2y (NH3 (CH2 )2 NH3 )2y Pb1-y I3 (0≤y≤0.25).

Tuning the optical properties of MAPbI3 (MA=methylammonium) is a key requirement to increase the efficiency of perovskite solar cells (PSCs). Simple precipitation from solution allows the partial substitution of MA in MAPbI3 by H3 NCH2 CH2 NH3 (H2 en). Surprisingly, there is 1:1 exchange of the monovalent cation MA by the dication H2 en. The charge compensation results from a deficit of Pb2+ , leading to a series MA1-2y (H2 en)2y Pb1-y I3 with 0≤y≤0.25. This model has been supported by single-crystal measurements and NMR investigations. The substitution results in a continuous shift of the band gap from 1.51 to 2.1 eV and a color change from black to orange-red. The H2 en content stabilizes the cubic high-temperature (HT) form of MAPbI3 . There is a linear correlation between band gap and unit cell volume. The substitution enables controlled band gap tuning because the extent of substitution is closely related to the applied MA:H2 en ratio in solution.

Synthesis, Crystal Structure, and Properties of Bi3 TeBO9 or Bi3 (TeO6 )(BO3 ): A Non-Centrosymmetric Borate-Tellurate(VI) of Bismuth.

Pale-yellow single crystals of the new borate tellurate(VI) Bi3 TeBO9 were obtained by reaction of stoichiometric amounts of Bi2 O3 , B2 O3 , and Te(OH)6 at 780 °C. The non-centrosymmetric crystal structure (P63 , Z=2, a=8.7454(16), c=5.8911(11) Å, 738 refl., 43 param, R1=0.037, wR2=0.093) contains isolated trigonal-planar BO3 units and nearly undistorted TeO6 octahedra. The Bi3+ cations are located in between in octahedral voids. The BiO6 octahedra are significantly distorted to a [3+3] pattern (2.25/2.50 Å) due to the ns2 configuration. According to the structural features, the formula can be written as Bi3 (TeO6 )(BO3 ). Alternatively, the structure can also be described as hcp of oxygen with TeVI and BiIII in octahedral voids and BIII in trigonal- planar voids. The vibrational spectra show the typical features of BO3 and TeO6 units with a significant 10 B/11 B isotopic splitting of the IR-active B-O valence mode (1248 and 1282 cm-1 ). The UV/Vis spectrum shows an optical band edge with an onset around 480 nm (2.6 eV). MAS-NMR spectra of 11 B show an anisotropic signal with a quadrupole coupling constant of CQ =2.55 MHz. and a very small deviation from rotational symmetry (η=0.2). The isotropic chemical shift is 20.1 ppm. The second harmonic generation (SHG) test was positive with an activity comparable to potassium dihydrogen phosphate (KDP). Bi3 TeBO9 decomposes in air at 825 °C to Bi2 TeO5 .

AlFe2-xCoxB2 (x = 0-0.30): TC Tuning through Co Substitution for a Promising Magnetocaloric Material Realized by Spark Plasma Sintering.

AlFe2B2 and AlFe2-xCoxB2 (x = 0-0.30) were synthesized from the elements in three different ways. The samples were characterized by powder X-ray diffraction, Rietveld refinements, energy-dispersive X-ray spectroscopy, and magnetic measurements. Using Al flux the formation of AlFe2B2 single crystals is preferred. Arc melting enables the substitution of ∼6% Co. This substitution of Fe by Co decreases the Curie temperature TC from 290 to 240 K. The highest Co substitution up to 15% is achieved by spark plasma sintering (SPS). TC is reduced to 205 K. In all cases an excess of Al is necessary to avoid the formation of ferromagnetic FeB. Al13Fe4-xCox is the common byproduct. TC and the cobalt content are linearly correlated. The transition paramagnetic-ferromagnetic remains sharp for all examples. The magnetic entropy change of the Co-containing samples is comparable to AlFe2B2. SPS synthesis yields, in short reaction times, a homogeneous and dense material with small amounts of paramagnetic Al13Fe4-xCox as an impurity, which can serve as sinter additive. These properties make AlFe2-xCoxB2 a promising magnetocaloric material for applications between room temperature and 200 K.

The first boroselenates as new silicate analogues.

The first boroselenates were obtained as single crystals by the reaction of selenic acid with boron acid and the corresponding alkali carbonates. The structure determinations showed a far-reaching analogy to very recently described borosulfates and the borophosphates, that is, tetrahedral BO4 and SeO4 units linked by common corners. In each case, the BO4 tetrahedra are surrounded by SeO4 tetrahedra. As a function of the B/Se ratio, this results in chains (1:3; Cs3 [B(SeO4)3], Rb3 [B(SeO4)3]), isolated pentamers (1:4; HK4 [(B(SeO4)4]), or pentamers with additional isolated SeO4 tetrahedra (1:5; (H3 O)Na6 [B(SeO4 )4 ](SeO4). Compound Rb3 [B(SeO4)3] (orthorhombic, Ibca, Z=8, a=7.508(2), b=15.249(3), c=23.454(5) Å) is isotypic to Rb3 [B(SO4)3]) and Ba3 [B(PO4)3]. Compound Cs3 [B(SeO4)3] (monoclinic, P21 /c, Z=4, a=11.3552(4), b=7.9893(3), c=15.7692(6) Å, ß=101.013(1)°) represents a distorted variant of Rb3 [B(SeO4)3]. The isolated pentamers in HK4 [(B(SeO4)4]) (triclinic, P$\bar 1$, Z=6, a=7.5303(1), b=7.5380(1), c=42.3659(4) Å, α=88.740(1), ß=89.971(1), γ=89.971(1)°) were also found in K5 [(B(SO4)4] and Na5 [(B(SO4)4]. Compound (H3 O)Na6 [B(SeO4)4](SeO4) (tetragonal, I$\bar 4$, a=9.9796(1), c=18.2614(2) Å) is a super structure of the borophosphates Sr6 [B(PO4)4](PO4) and Pb6 [B(PO4)4](PO4). Because the tetrahedra are only connected through apices, there are topological analogies to silicates. Therefore, boroselenates may have a similar variability of crystal structures, such as borosulfates and borophosphates.

Ternary Borides Cr2AlB2, Cr3AlB4, and Cr4AlB6: The First Members of the Series (CrB2)nCrAl with n = 1, 2, 3 and a Unifying Concept for Ternary Borides as MAB-Phases.

Single crystals of the ternary borides Cr2AlB2, Cr3AlB4, Cr4AlB6, MoAlB, WAlB, Mn2AlB2, and Fe2AlB2 were grown from the elements with an excess of Al. Structures were refined by X-ray methods on the basis of single crystal data. All compounds crystallize in orthorhombic space groups. In each case boron atoms show the typical trigonal prisms BM6. The BM6-units are linked by common rectangular faces forming B-B-bonds. Thus, zigzag chains of boron atoms are obtained for MoAlB, WAlB, and M2AlB2 (M = Cr, Mn, Fe); chains of hexagons for Cr3AlB4; and double chains of hexagons for Cr4AlB6. The same subunits are known for the binary borides CrB, Cr3B4, Cr2B3, and ß-WB, too. The boride partial structures are separated by single layers of Al-atoms in the case of the chromium compounds and double layers for WAlB, i.e., W2Al2B2. All crystal structures can be described using a unified building set principle with quadratic 4(4)-nets of metal atoms. The different compositions and crystal structures are obtained by different numbers of metal layers in the corresponding parts according to the formula (MB)2Aly(MB2)x. This principle is an extension of a scheme which was developed for the boridecarbides of niobium. Furthermore, there is a close similarity to the group of ternary carbides MAl(MC)n, so-called MAX-phases. Therefore, they might be named as "MAB-phases". The pronounced two-dimensionality and the mixture of strong covalent and metallic interactions make MAB-phases to promising candidates for interesting material properties. All compositions were confirmed by EDX measurements. Additionally, microhardness measurements were performed.

Synthesis, crystal structure, and spectroscopy of the mixed-valent boroseleniteselenate B2Se3O10.

The first mixed-valent boroseleniteselenate B2Se3O10 was obtained as a colorless, hygroscopic compound from the reaction of boric acid (H3BO3) in concentrated selenic acid (H2SeO4) at 265 °C. H2SeO4 can be replaced by appropriate amounts of SeO2 and H2O2. The crystal structure was determined from single-crystal data (P21/c, Z = 4, a = 4.3466(2) Å, b = 7.0237(4) Å, c = 22.1460(9) Å, ß = 94.922(2)°, R1 = 0.036, wR2 = 0.096). It represents a new structure type that is characterized by a 3D net of BO4 tetrahedra, Se(VI)O4 tetrahedra, and trigonal-pyramidal Se(IV)O3 in a ratio of 2:1:2. (77)Se magic-angle-spinning NMR investigations confirm the mixed-valent character because the chemical shifts are found in the typical regions, i.e., 1278 and 1202 ppm for Se(IV) and 972 ppm for Se(VI). The vibrational spectra show the typical modes according to the present polyhedra. In addition, NMR and vibrational spectra of the closely related B2Se2O7 are presented.

Synthesis, single-crystal structure and characterization of (CH3 NH3 )2 Pb(SCN)2 I2.

The perovskite phase (CH3 NH3 )2 Pb(SCN)2 I2 with a structure closely related to the K2 NiF4 -type was identified as the product of the reaction of CH3 NH3 I and Pb(SCN)2 by single-crystal X-ray analysis. This extends the range of suitable dyes for solar cell applications to a class of perovskite-related structures of the general composition (AMX3 )n (AX)m .

The borosulfate story goes on--from alkali and oxonium salts to polyacids.

The structural principles of borosulfates derived from the B/S ratio are confirmed and extended to new representatives of this class showing novel motifs. According to the composition, Na[B(S2O7)2] (P2(1)/c; a=10.949(6), b=8.491(14), c=12.701(8) Å; ß=110.227(1)°; Z=4) and K[B(S2O7)2] (Cc; a=11.3368(6), b=14.662(14), c=13.6650(8) Å; ß=94.235(1)°; Z=8) contain isolated [B(S2O7)2](-) ions, in which the central BO4 tetrahedron is coordinated by two disulfate units. The alkali cations have coordination numbers of 7 (Na) and 8 (K), respectively. The structure of Cs[B(S2O7)(SO4)] (P2(1)/c; a=10.4525(6), b=11.3191(14), c=8.2760(8) Å; ß=103.206(1); Z=4) combines, for the first time, sulfate and disulfate units into a chain structure. Cs has a coordination number of 12. The same structural units were found in H[B(S2O7)(SO4)] (P2(1)/c; a=15.6974(6), b=11.4362(14), c=8.5557(8) Å; ß=90.334(3)°; Z=8). This compound represents the first example of a polyacid. The hydrogen atoms were located and connect the chains to form layers through hydrogen-bonding bridges. H3O[B(SO4)2] (P4/ncc; a=9.1377(6), c=7.3423(8) Å; Z=4) is the first oxonium compound of this type to be found. The BO4 tetrahedra are linked by SO4 tetrahedra to form linear chains similar to those in SiS2. The chains form a tetragonal rod packing structure with H3O(+) between the rods. The structures of borosulfates can be classified following the concept described by Liebau for silicates, which was extended to borophosphates by Kniep et al. In contrast to these structures, borosulfates do not comprise B-O-B bonds but instead contain S-O-S connections. All compounds were obtained as colourless, moisture-sensitive single crystals by reaction of B2O3 and the appropriate alkali salt in oleum.

Exploring a new structure family: alkali borosulfates Na5[B(SO4)4], A3[B(SO4)3] (A = K, Rb), Li[B(SO4)2], and Li[B(S2O7)2].

New alkali borosulfates were obtained by precipitation from oleum, solid-state reactions, or thermal decomposition. The crystal structures were characterized with single-crystal data. They are all based on corner-linked BO4 and SO4 tetrahedra with varying coordination of the alkali cations. According to the ratio of BO4 and SO4 tetrahedra, different frameworks are observed, i.e., noncondensed complex anions (1:4), one-dimensional chains (1:3), or three-dimensional (3D) networks (1:2). This is in analogy to silicates, where the ratio Si/O relates to the dimensionality also. For Na5[B(SO4)4], which exists in two different polymorphs, there are noncondensed pentameric units. Na5[B(SO4)4]-I: space group Pca21, a = 10.730(2) Å, b = 13.891(3) Å, c = 18.197(4) Å. Na5[B(SO4)4]-II: space group P212121, a = 8.624(2) Å, b = 9.275(2) Å, c = 16.671(3) Å. A3[B(SO4)3] (A = K, Rb) are isotypic with Ba3[B(PO4)3] adopting space group Ibca [K3[B(SO4)3], a = 7.074(4) Å, b = 14.266(9) Å, c = 22.578(14) Å; Rb3[B(SO4)3], a = 7.2759(5) Å, b = 14.7936(11) Å, c = 22.637(2) Å] with vierer chains of BO4tetrahedra based on two bridging and two terminal SO4 tetrahedra. Li[B(SO4)2] [space group Pc, a = 7.6353(15) Å, b = 9.342(2) Å, c = 8.432(2) Å, and ß = 92.55(2)°] comprises a 3D network that is closely related to ß-tridymite. Li[B(S2O7)2] [space group P212121, a = 10.862(2) Å, b = 10.877(2) Å, c = 17.769(4) Å] represents the first example of a disulfate complex with noncondensed [B(S2O7)2](-) units. Vibrational spectra were recorded from all compounds, and the thermal behavior was also investigated.

Synthesis, structure, and properties of the new mixed-valent dodecahalogenotrimetallate In4Ti3Br12 and its relation to compounds A3Ti2X9 (A = K, In; X = Cl, Br).

Black single crystals of the new dodecahalogenotrimetallate In(4)Ti(3)Br(12) were obtained by reacting InBr(3) with Ti-wire at 450 °C in a silica tube sealed under vacuum. In(4)Ti(3)Br(12) (Pearson symbol hR57, space group R3m, Z = 3, a = 7.3992(8) Å, c = 36.673(6) Å, 643 refl., 25 param., R(1)(F) = 0.025; wR(2)(F(2)) = 0.046) is a defect variant of a 12 L-perovskite. In(+) cations are 12-fold coordinated in two different ways: In1 as an anticuboctahedron and In2 as a cuboctahedron. In both cases the 5s(2) configuration results in 3 short, 6 medium, and 3 long In-Br distances which might be explained as lone pair effect or second order Jahn-Teller instability. Furthermore there are isolated linear trimers [Ti(3)Br(12)](4-) consisting of facesharing octahedra similar to [Ru(3)Cl(12)](4-). The [Ti(3)Br(12)](4-)-unit has to be described as a mixed-valent d(1)-d(2)-d(1) system. According to magnetic measurements, the Ti-atoms in In(4)Ti(3)Br(12) show strong antiferromagnetic interactions (Θ = -1216(6) K) which might be addressed as weak Ti(3+)-Ti(2+)-Ti(3+) bonds. For comparison, single crystals of K(3)Ti(2)X(9) (X = Cl, Br) were synthesized and their structures refined. The rotation of the Ti(2)X(9)(3-) dimers reduced the symmetry of the well-known Cs(3)Cr(2)Cl(9) type from P6(3)/mmc to P6(3)/m and resulted in the formation of merohedral twins. According to the unit cell volumes In(+) is smaller than K(+) in all cases.

LiB12PC, the first boron-rich metal boride with phosphorus--synthesis, crystal structure, hardness, spectroscopic investigations.

We present synthesis, crystal structure, hardness, and IR/Raman and UV/Vis spectra of a new compound with the mean composition LiB(12)PC. Transparent single crystals were synthesised from Ga, Li, B, red phosphorus and C at 1500 °C in boron nitride crucibles welded in Ta ampoules. Depending on the type of boron used for the synthesis we obtained colourless, brown and red single crystals with slightly different P/C ratios. Colourless LiB(12)PC crystallizes orthorhombic in the space group Imma (No. 74) with a=10.188(2) Å, b=5.7689(11) Å, c=8.127(2) Šand Z=4. Brown LiB(12)P(0.89)C(1.11) is very similar, but with a lower P content. Red single crystals of LiB(12)P(1.13)C(0.87) have a larger unit cell with a=10.4097(18) Å, b=5.9029(7) Å, c=8.2044(12) Å. EDX measurements confirm that the red crystals contain more phosphorus than the other ones. The crystal structure is characterized by a covalent network of B(12) icosahedra connected by exohedral B-B bonds and P-P, P-C or C-C units. Li atoms are located in interstitials. The structure is closely related to MgB(7), LiB(13)C(2) and ScB(13)C. LiB(12)PC fulfils the electron counting rules of Wade and also Longuet-Higgins. Measurements of Vickers micro-hardness (H(V)=27 GPa) revealed that LiB(12)PC is a hard material. The optical band gaps obtained from UV/Vis spectra match the colours of the crystals. Furthermore we report on the IR and Raman spectra.

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.

Synthesis, crystal structure, and properties of Mg(x)B50C8 or Mg(x)(B12)4(CBC)2(C2)2 (x = 2.4-4).

Single crystals of a new magnesium boride carbide Mg(x)B(50)C(8) (x = 2.4-4) were synthesized from the elements in a metallic melt using tantalum ampules. Crystals were characterized by single crystal X-ray diffraction and electron microprobe analysis. The variation of the Mg content results from different reaction conditions. The composition Mg(∼3)B(50)C(8) is by far the most favored. It fulfills the electron counting rules of Wade and Longuet-Higgins and thus explains the light-green to yellow transparent color. The structure of Mg(∼3)B(50)C(8) (C2/m, Z = 1, a = 8.9384(12) Å, b = 5.6514(9) Å, c = 9.6021(13) Å, ß = 105.86(1)°) consists of B(12) icosahedra. The icosahedra are interconnected by four exohedral B-B bonds to layers. The layers are connected to a three-dimensional covalent network by C(2) and CBC units and further exohedral B-B bonds. The Mg sites are partially occupied. Different site occupation factors cause the various compositions and colors (Mg(2.4)B(50)C(8), brown; Mg(4)B(50)C(8), black). The vibrational spectra show the modes of B(12) icosahedra and C(2) and CBC units as well. Measurements of the microhardness according to Vickers and Knoop revealed remarkably high values of H(V) = 3286 (32.0 GPa) and H(K) = 3165 (31.5 GPa), which exceed the values of B(4)C. Optical spectra reveal a band gap of 2.7 eV for Mg(∼3)B(50)C(8), in agreement to the observed color. This justifies an ionic description, and the formula can be written as (Mg(2+))(3)(B(12)(2-))(4)(CBC(+))(2)(C(2))(2).

Binary boron-rich borides of magnesium: single-crystal investigations and properties of MgB(7) and the new boride Mg(∼5)B(44).

Single crystals of dark-red MgB(7) were grown from the elements in a Cu-melt. The crystal structure (Pearson symbol oI64; space group Imma; a = 10.478(2) Å, b = 5.977(1) Å, c = 8.125(2) Å, 2842 reflns, 48 params, R(1)(F) = 0.018, R(2)(I) = 0.034) consists of a hexagonal-primitive packing of B(12)-icosahedra and B(2)-units in trigonal-prismatic voids. According to the UV-vis spectra and band structure calculations MgB(7) is semiconducting with an optical gap of 1.9 eV. The long B-B distance of 2.278 Å within the B(2)-unit can be seen as a weak bonding interaction. The new Mg(∼5)B(44) occurs beside the well-known MgB(12) as a byproduct. Small fragments of the black crystals are dark-yellow and transparent. The crystal structure (Pearson symbol tP196, space group P4(1)2(1)2, a = 10.380(2) Å, c = 14.391(3) Å, 4080 reflns, 251 params, R(1)(F) = 0.025, R(2)(I) = 0.037) is closely related to tetragonal boron-II (t-B(192)). It consists of B(12)-icosahedra and B(19+1)-units. With a charge of -6 for the B(19+1)-units and a Mg-content of ∼20 Mg-atoms per unit cell the observed Mg content in Mg(∼5)B(44) is quite close to the expected value derived from simple electron counting rules. All compositions were confirmed by EDXS. The microhardness was measured on single crystals for MgB(7) (H(V) = 2125, H(K) = 2004) and MgB(12) (H(V) = 2360, H(K) = 2459).