The structure and thermal decomposition of Y(BH 4 ) 3 is studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD), 11 B MAS NMR spectroscopy, and thermal analysis (thermogravimetric analysis/differential scanning calorimetry). The samples were prepared via a metathesis reaction between LiBH 4 and YCl 3 in different molar ratios mediated by ball milling. A new high temperature polymorph of Y(BH 4 ) 3 , denoted β-Y(BH 4 ) 3 , is discovered besides the Y(BH 4 ) 3 polymorph previously reported, denoted R-Y(BH 4 ) 3 . β-Y(BH 4 ) 3 has a cubic crystal structure and crystallizes with the space group symmetry Pm3m and a bisected a-axis, a = 5.4547(8) Å , as compared to R-Y(BH 4 ) 3 , a = 10.7445(4) Å (Pa3). β-Y(BH 4 ) 3 crystallizes with a regular ReO 3 -type structure, hence the Y 3þ cations form cubes with BH 4 -anions located on the edges. This arrangement is a regular variant of the distorted Y 3þ cube observed in R-Y(BH 4 ) 3 , which is similar to the high pressure phase of ReO 3 . The new phase, β-Y(BH 4 ) 3 is formed in small amounts during ball milling; however, larger amounts are formed under moderate hydrogen pressure via a phase transition from R-to β-Y(BH 4 ) 3 , at ∼180°C. Upon further heating, β-Y(BH 4 ) 3 decomposes at ∼190°C to YH 3 , which transforms to YH 2 at 270°C. An unidentified compound is observed in the temperature range 215-280°C, which may be a new Y-B-H containing decomposition product. The final decomposition product is YB 4 . These results show that boron remains in the solid phase when Y(BH 4 ) 3 decomposes in a hydrogen atmosphere and that Y(BH 4 ) 3 may store hydrogen reversibly.

A new alkaline transition-metal borohydride, NaSc(BH 4 ) 4 , is presented. The compound has been studied using a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. NaSc(BH 4 ) 4 forms at ambient conditions in ball-milled mixtures of sodium borohydride and ScCl 3 . A new ternary chloride Na 3 ScCl 6 (P2 1 /n, a ) 6.7375), isostructural to Na 3 TiCl 6 , was identified as an additional phase in all samples. This indicates that the formation of NaSc(BH 4 ) 4 differs from a simple metathesis reaction, and the highest scandium borohydride yield (22 wt %) was obtained with a reactant ratio of ScCl 3 /NaBH 4 of 1:2. NaSc(BH 4 ) 4 crystallizes in the orthorhombic crystal system with the space group symmetry Cmcm (a ) 8.170(2) Å, b ) 11.875(3) Å, c ) 9.018(2) Å, V ) 874.9(3) Å 3 ). The structure of NaSc(BH 4 ) 4 consists of isolated homoleptic scandium tetraborohydride anions, [Sc(BH 4 ) 4 ] -, located inside slightly distorted trigonal Na 6 prisms (each second prism is empty, triangular angles of 55.5 and 69.1°). The experimental results show that each Sc 3+ is tetrahedrally surrounded by four BH 4 tetrahedra with a 12-fold coordination of H to Sc, while Na + is surrounded by six BH 4 tetrahedra in a quite regular octahedral coordination with a (6 + 12)-fold coordination of H to Na. The packing of Na + cations and [Sc(BH 4 ) 4 ] -anions in NaSc(BH 4 ) 4 is a deformation variant of the hexagonal NiAs structure type. NaSc(BH 4 ) 4 is stable from RT up to ∼410 K, where the compound melts and then releases hydrogen in two rapidly occurring steps between 440 and 490 K and 495 and 540 K. Thermal expansion of NaSc(BH 4 ) 4 between RT and 408 K is anisotropic, and lattice parameter b shows strong anomaly close to the melting temperature.

After having emerged as primary contenders in the race for highly efficient optoelectronics materials, organolead halide perovskites (OHLP) are now being investigated in the nanoscale regime as promising building blocks with unique properties. For example, unlike their bulk counterpart, quantum dots of OHLP are brightly luminescent, owing to large exciton binding energies that cannot be rationalized solely on the basis of quantum confinement. Here, we establish the direct correlation between the structure and the electronic band-edge properties of CH3NH3PbBr3 nanoparticles. Complementary structural and spectroscopic measurements probing long-range and local order reveal that lattice strain influences the nature of the valence band and modifies the subtle stereochemical activity of the Pb(2+) lone-pair. More generally, this work demonstrates that the stereochemical activity of the lone-pair at the metal site is a specific physicochemical parameter coupled to composition, size and strain, which can be employed to engineer novel functionalities in OHLP nanomaterials.