Volume 79, Issue 1 - Special issue dedicated to Professor Wolfgang Bensch of the University of Kiel on the occasion of his 70th birthday

The TiMnSi 2 -type (space group Pbam ) germanides Sc T Ge 2 ( T = Fe, Co, Ru, Rh) were synthesized from the elements by arc-melting. Single crystals were grown by annealing sequences of the arc-melted buttons in an induction furnace. The structures of ScFeGe 2 , ScRuGe 2 and ScRhGe 2 were refined from single-crystal X-ray diffraction data. In ScRuGe 2 , the ruthenium atoms have distorted octahedral germanium coordination (242–268 pm Ru–Ge). Three trans -face-sharing octahedra form a sub-unit which is condensed via common edges in c direction and connected via common corners with four adjacent blocks, forming a three-dimensional [RuGe 2 type] substructure. The two crystallographically independent scandium sites have coordination numbers 15 (Sc1@Ge 8 Ru 4 Sc 3 ) and 17 (Sc2@Ge 7 Ru 6 Sc 4 ). Electronic band structure calculations for ScCoGe 2 and ScRuGe 2 show a net charge transfer from the scandium to the transition metal and germanium atoms, leading to a description with polyanionic networks Sc δ + [ T Ge 2 ] δ− . The two crystallographically independent Sc sites are easily distinguishable by 45 Sc magic-angle spinning (MAS)-NMR spectroscopy. Isotropic chemical shift values and nuclear electric quadrupolar interaction parameters were deduced from an analysis of the triple-quantum (TQ)-MAS NMR spectra. The electric field gradient parameters deduced from these experiments are in good agreement with quantum-chemical calculations using the Wien 2 k code. Likewise, the two crystallographically independent iron sites in ScFeGe 2 could be discriminated in the 57 Fe Mößbauer spectra through their isomer shifts and quadrupole splitting parameters: δ = 0.369(1) mm s −1 and ∆ E Q = 0.232(2)  mm s −1 for Fe1 and δ = 0.375(2) mm s −1 and ∆ E Q = 0.435(4) mm s −1 for Fe2 (data at T = 78 K).

The intermetallic ytterbium compounds YbZnSn, YbPdSn 2 , YbAuIn 2 and their calcium-substituted counterparts Yb 0.5 Ca 0.5 ZnSn, Yb 0.5 Ca 0.5 PdSn 2 and Yb 0.5 Ca 0.5 AuIn 2 were synthesized by reaction of the elements in sealed tantalum tubes in an induction furnace. The samples were characterized by X-ray powder diffraction. Their static, temperature-dependent solid-state 171 Yb NMR spectra exhibit strong positive Knight shifts without any significant temperature dependence. The resonance shifts including anisotropy parameters for the ternary compounds have been determined.

The solid solutions Eu 2 Al 15 (Pt 1− x T x ) 6 with T = Pd, Ir, Au and x = 1/6 were prepared by arc-melting the stoichiometric mixture of the elements, and subsequent annealing. For x = 1/6, all three solid solutions adopt the same structure type as Eu 2 Al 15 Pt 6 according to powder X-ray diffraction data. Since the platinide Eu 2 Al 15 Pt 6 exhibits a (3 + 1)D modulated structure (approximant in space group P 12 1 / m 1), only the averaged hexagonal unit cell ( P 6 3 / mmc , Sc 0.6 Fe 2 Si 4.9 type) was refined by the Rietveld method. Scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy (SEM/EDX) showed that the degree of substitution is in line with the weighed amounts. For values of x > 1/6, no phase-pure samples could be obtained. The results of the magnetic susceptibility measurements indicate that the isoelectronic substitution of Pd for Pt lowers the temperature of the first-order valence phase transition from T trans = 45 K in Eu 2 Al 15 Pt 6 to T trans = 42 K in Eu 2 Al 15 (Pt 5/6 Pd 1/6 ) 6 . For Eu 2 Al 15 (Pt 5/6 Ir 1/6 ) 6 and Eu 2 Al 15 (Pt 5/6 Au 1/6 ) 6 a change in the electronic situation occurs since the Ir substituted compound exhibits one electron less compared to the pristine Pt compound, while Eu 2 Al 15 (Pt 5/6 Au 1/6 ) 6 has one additional electron. As a consequence, Eu 2 Al 15 (Pt 5/6 Ir 1/6 ) 6 shows a higher valence phase transition temperature of T trans = 52 K while for Eu 2 Al 15 (Pt 5/6 Au 1/6 ) 6 no such transition is obvious.

Cesium-containing thioarsenates(V) of lanthanoids with the composition Cs 3 Ln [AsS 4 ] 2 can be prepared for Ln = La–Nd and Sm by the oxidation of the lanthanoid metals in the presence of orpiment (As 2 S 3 ), cesium sesquisulfide (Cs 2 S 3 ) and elemental sulfur (S). The reaction mixtures were handled under argon atmosphere and heated in fused silica ampoules to a moderate reaction temperature of 500 °C. Single crystals of this Cs 3 Ln [AsS 4 ] 2 series appear as yellowish, transparent rods that are not stable to moist air and water. Their monoclinic crystal structure was determined from single-crystal X-ray diffraction data. The cesium-containing thioarsenates(V) Cs 3 Ln [AsS 4 ] 2 with Ln = La–Nd and Sm crystallize isotypically with Rb 3 Sm[PS 4 ] 2 in the non-centrosymmetric monoclinic space group P 2 1 with Z = 2. The lattice parameters range between a = 997–1015 pm, b = 699–703 pm, c = 1192–1195 pm and β = 90.2–90.4°. There are two crystallographically different As 5+ cations and one unique Ln 3+ cation present, all coordinated by sulfur anions. Tetrahedral [AsS 4 ] 3− anions form two functionally different units working either as bridging units between three Ln 3+ cations or as terminal ligands for Ln 3+ . [ Ln S 8 ] 13− polyhedra form ∞ 1 { [ Ln S 2 / 2 v S 6 / 1 t ] 11 − } ${}_{\infty }^{1}\left\{{[\mathit{Ln}{\mathrm{S}}_{2/2}^{\mathrm{v}}{\mathrm{S}}_{6/1}^{\mathrm{t}}]}^{11-}\right\}$ chains propagating along [010], which are separated by Cs + cations with coordination numbers as high as C.N. = 9, 10 and 11. Surprisingly, the eighth interatomic distance d ( Ln –S3) does not follow the lanthanoid contraction, but increases with decreasing ionic radius, changing the coordination polyhedron of Ln 3+ from a bicapped to a monocapped trigonal prism upon the transition from Nd to Sm, and causing a structural break in the crystal structure of this series. The results of Raman spectroscopic measurements on single crystals of Cs 3 La[AsS 4 ] 2 have confirmed the presence of [AsS 4 ] 3− tetrahedra as structural building blocks.

Five transition metal borates were synthesized in a Walker-type module under high-pressure/high-temperature conditions of 8–9 GPa and 800–1200 °C. They all exhibit the same interpenetrating, anionic borate network B 12 O 26 16− , crystallizing in the space group I 4 1 / acd , and therefore show high similarities to the borates Ti 5 B 12 O 26 and Ga 5 B 12 O 25 (OH). Cr 5 B 12 O 25 (OH) and V 5 B 12 O 25 (OH) are isotypic to Ga 5 B 12 O 25 (OH), whereas Mn 5 Mn 0.83 B 12 O 26 and Fe 5 Fe 0.14 B 12 O 24.3 (OH) 1.7 feature the partial occupation of an additional, cuboctahedral cavity in the structure. This is due to a partial reduction of the cations to the oxidation state +2, as presented with the novel compound Mn 5 MnB 12 O 22 (OH) 4 , which only features Mn 2+ for charge compensation. These structures feature a twelvefold coordination of manganese and iron.

The new zinc borate Zn 3 B 7 O 13 (OH) crystallizes trigonally in the space group R 3 c (no. 161) with the lattice parameters a  = 849.76(3), c  = 2099.8(2) pm, V  = 1.3131(2) nm 3 , and six formula units per unit cell ( Z  = 6). It was synthesized at high-pressure/high-temperature conditions in a multianvil device. Single-crystal and powder X-ray diffraction experiments were conducted.

The compounds [Me 3 N(C 6 H 3 (CF 3 ) 2 )][BF 4 ] and [Me 3 N(C 6 H 3 (CH 3 ) 2 )][BF 4 ] were synthesized from commercially available starting materials and fully characterized by single-crystal X-ray diffraction, NMR, IR and Raman spectroscopy, as well as mass spectrometry. Both ammonium cations show potential for applications in crystal engineering due to their structure directing properties in the solid state.