Borohydrides have attained high interest in the past few years due to their high volumetric and gravimetric hydrogen content. Synthesis of di/trimetallic borohydride is a way to alter the thermodynamics of hydrogen release from borohydrides. Previously reported preparations of M(BH₄)₂ involved chloride containing species such as SrCl₂. The presence of residual chloride (or other halide) ions in borohydrides may change their thermodynamic behavior and their decomposition pathway. Pure monometallic borohydrides are needed to study decomposition products without interference from halide impurities. They can also be used as precursors for synthesizing di/trimetallic borohydrides. In this paper we present a way to synthesize halide free alkaline earth metal (Sr, Ba) and europium borohydrides starting with the respective hydrides as precursors. Two novel high temperature polymorphs of Sr and Eu borohydrides and four polymorphs of Ba borohydride have been characterized by synchrotron X-ray powder diffraction, thermal analysis, and Raman and infrared spectroscopy and supported by periodic DFT calculations. The decomposition routes of these borohydrides have also been investigated. In the case of the decomposition of strontium and europium borohydrides, the metal borohydride hydride (M(BH₄)H₃, M = Sr, Eu) is observed and characterized. Periodic DFT calculations performed on room temperature Ba(BH₄)₂ revealed the presence of bidentate and tridentate borohydrides.

Elongated plasmonic nanoparticles show superior optical properties when compared to spherical ones. Facile, versatile and cost-effective bottom-up approaches for fabrication of anisotropic nanoparticles in solution have been developed. However, fabrication of 2-D plasmonic templates from elongated nanoparticles with spatial arrangement at the surface is still a challenge. We used controlled seed-mediated growth in the presence of porous and functionalized surface of flexible polydimethylsiloxane (PDMS) templates to provide directional growth and formation of elongated gold nanoparticles (AuNPs). Atomic force microscopy (AFM) and spectroscopy revealed embedding of the particles within the functionalized porous surface of PDMS. Nanoparticles shapes were observed with transmission electron microscope (TEM), UV–Vis spectroscopy, and X-ray powder diffraction (XRPD) measurements, which revealed an overall orientation of particles at the surface. Anisotropic and oriented particles on a flexible substrate are of interest for sensing applications.

The structural phase transitions occurring in a series of perovskite-type complex hydrides based on the tetrahydroborate anion BH₄^- are investigated by means of in situ synchrotron x-ray powder diffraction, vibrational spectroscopy, thermal methods and ab initio calculations in the solid state. Structural dynamics of the BH4 anion are followed with quasi-elastic neutron scattering. We show that unexpected temperature-induced lattice instabilities in perovskite-type ACa(BH₄)₃ (A = K, Rb, Cs) have their origin in close hydridic di-hydrogen contacts. The rich lattice dynamics lead to coupling between internal B-H vibrations and phonons, resulting in distortions in the high-temperature polymorph that are identical in symmetry to well-known instabilities in oxide perovskites, generally condensing at lower temperatures. It is found that anion-substitution BH₄^-  ↔ X^- (X = Halide) can relax distortions in ACa(BH4)3 by eliminating coulomb repulsive H- • • • H^- effects. The interesting nature of phase transition in ACa(BH4)3 enters an unexplored field of weak interactions in ceramic-like host lattices and is the principal motivation for this study. Close di-hydrogen contacts suggest new concepts to tailor crystal symmetries in complex hydride perovskites in the future.

Borohydrides are actively considered as potential hydrogen storage materials. In this context fundamental understanding of breaking and forming B-H bond is essential. Isotope exchange reactions allow isolating some parts of this reaction without introducing major structural or chemical changes. Experiments were performed on Ca(BH₄)₂and Ca(BD₄)₂ as a function of temperature and pressure. A complete exchange can be realized in about 9h at 200 °C using a deuterium pressure of 20 bar. The activation energy, estimated using first order kinetics, for the forward reaction (Ca(BH₄)₂ → Ca(BD₄)₂) was found to be 82.1 ± 2.7 kJ/mol (P = 35 bar) and the one for the backward reaction (Ca(BD₄)₂ → Ca(BH₄)₂) was found to be 98.5 ± 8.3 kJ/mol (P = 35 bar). Pressure dependent study shows that the reaction rate increases with increasing pressure up to 35 bar. This behavior is consistent with first adsorption step prior to diffusion into the solid and isotope exchange according to the scheme described below.

To celebrate the International Year of Crystallography among the general public, a consortium of chemists, physicists and crystallographers of the University of Geneva organised in Spring 2014 an incentive crystal growth contest for Geneva scholars aged 4 to 19. Starting from a kit containing a salt and user instructions, classes had to prepare a crystal that met specific criteria according to their category of age. The composition of the salt – potassium dihydrogen phosphate (KDP) – was only disclosed to the participants during the final Awards Ceremony. This contest positively exceeded our expectations with almost 100 participating classes (ca. 1800 participants) and 54 specimens received over all categories.

Perovskite materials host an incredible variety of functionalities. Although the lightest element, hydrogen, is rarely encountered in oxide perovskite lattices, it was recently observed as the hydride anion H^−, substituting for the oxide anion in ​BaTiO₃. Here we present a series of 30 new complex hydride perovskite-type materials, based on the non-spherical ​tetrahydroborate anion ​BH₄^− and new synthesis protocols involving rare-earth elements. Photophysical, electronic and ​hydrogen storage properties are discussed, along with counterintuitive trends in structural behaviour. The electronic structure is investigated theoretically with density functional theory solid-state calculations. BH₄-specific anion dynamics are introduced to perovskites, mediating mechanisms that freeze lattice instabilities and generate supercells of up to 16 × the unit cell volume in AB(BH₄)₃. In this view, homopolar hydridic di-hydrogen contacts arise as a potential tool with which to tailor crystal symmetries, thus merging concepts of molecular chemistry with ceramic-like host lattices. Furthermore, anion mixing ​BH⁴−â†�X^− (X^−=C^l−, Br^−, I^−) provides a link to the known ABX₃ halides.

The crystal structure of the third polymorph of dibenzylsquaramide (Portell, A. et al., 2009), (fig. 1) has been determined from laboratory X-ray powder diffraction data by means of direct space methods using the computing program FOX. (Favre-Nicolin and Černý, 2002) The structure resolution has not been straightforward due to several difficulties on the indexing process and in the space group assignment. The asymmetric unit contains two different conformers, which has implied an additional difficulty during the Rietveld (Rietveld, 1969) refinement. All these issues together with particular structural features of disquaramides are discussed.

Four novel bimetallic borohydrides have been discovered, K₂M(BH₄)₄ (M = Mg or Mn), K₃Mg(BH₄)₅, and KMn(BH₄)₃, and are carefully investigated structurally as well as regarding their decomposition reaction mechanism by means of in situ synchrotron radiation powder X-ray diffraction (SR-PXD), vibrational spectroscopies (Raman and IR), thermal analysis (TGA and DTA), and ab initio density functional theory (DFT) calculations. Mechano-chemical synthesis (ball-milling) using the reactants KBH₄, α-Mg(BH₄)₂, and α-Mn(BH₄)₂ ensures chlorine-free reaction products. A detailed structural analysis reveals significant similarities as well as surprising differences among the two isomorphs K₂M(BH₄)₄, most importantly concerning the extent to which the complex anion [M(BH₄)₄]^2– is isolated in the structure. Anisotropic thermal expansion and an increase in symmetry at high temperatures in K₃Mg(BH₄)₅ is ascribed to the motion of BH₄ groups inducing hydrogen repulsive effects, and the dynamics of K₃Mg(BH₄)₅ are investigated. Decomposition in the manganese system proceeds via the formation of KMn(BH₄)₃, the first perovkite type borohydride reported to date.

A solid solution of magnesium and manganese borohydrides was studied by in situ synchrotron radiation X-ray powder diffraction and infrared spectroscopy. A combination of thermogravimetry, mass and infrared spectroscopy, and atomic emission spectroscopy were applied to clarify the thermal gas desorption of pure Mn(BH₄)₂ and a solid solution of composition Mg_0.5Mn_0.5(BH₄)₂. Mg_xMn_(1−x)(BH₄)₂ (x = 0–0.8) conserves the trigonal structure of Mn(BH₄)₂ at room temperature. Manganese is dissolved in the hexagonal structure of α-Mg(BH₄)₂, with the upper solubility limit not exceeding 10 mol.% at room temperature. There exists a two-phase region of trigonal and hexagonal borohydrides within the compositional rangex = 0.8–0.9 at room temperature. Infrared spectra show splitting of various vibrational modes, indicating the presence of two cations in the trigonal Mg_xMn_(1−x)(BH₄)₂ solid solutions, as well as the appearance of a second phase, hexagonal α-Mg(BH₄)₂, at higher magnesium contents. All vibrational frequencies are shifted to higher values with increasing magnesium content. The decomposition temperature of the trigonal Mg_xMn_(1−x)(BH₄)₂ (x = 0–0.8) does not vary significantly as a function of the magnesium content (433–453 K). The desorbed gas contains mostly hydrogen and 3–7.5 mol.% diborane B₂H₆, as determined from analyses of the Mn(BH₄)₂ and Mg_0.5Mn_0.5(BH₄)₂ samples. An eutectic relation between α-Mg(BH₄)₂ and LiBH₄ is observed. The solid solution Mg_xMn_(1−x)(BH₄)₂ is a promising material for hydrogen storage as it decomposes at a similar temperature to Mn(BH₄)₂, i.e. at a much lower temperature than pure Mg(BH₄)₂ without significantly losing hydrogen weight capacity thanks to substitution of Mn by Mg up to 80 mol.%. The questions of diborane release and reversibility remain to be addressed.

The synthesis of a novel alkali-metal aluminium borohydride NaAl(BH₄)_xCl_4−x from NaBH₄ and AlCl₃ using a solid state metathesis reaction is described. Structure determination was carried out using synchrotron powder diffraction data and vibrational spectroscopy. An orthorhombic structure (space group Pmn2₁) is formed which contains Na⁺ cations and complex [Al(BH₄,Cl)₄]^−anions. Due to the high chlorine content (1 ≤ x ≤ 1.43) the hydrogen density of the borohydride is only between 2.3 and 3.5 wt.% H₂ in contrast to the expected 14.6 wt.% for chlorine free NaAl(BH₄)₄. The decomposition of NaAl(BH₄)_xCl_4−x is observed in the target range for desorption at about 90 °C by differential scanning calorimetry (DSC), in situ Raman spectroscopy and synchrotron powder X-ray diffraction. Thermogravimetric analysis (TG) shows extensive mass loss indicating the loss of H₂ and B₂H₆ at about 90 °C followed by extensive weight loss in the form of chloride evaporation.

Several new studies of Mg(BH₄)₂ are reported. A 1:1 LiBH₄:Mg(BH₄)₂ mixture was studied by in situ synchrotron X-ray diffraction and reveals an eutectic behavior with the eutectic composition more rich in Mg(BH₄)₂, and the eutectic temperature lower than 456 K. No dual cation compound was observed in this experiment.

New vibrational spectra including INS data have been obtained and are compared with theoretical DFT calculations and recent NMR studies, showing good agreement.

A new potassium scandium borohydride, KSc(BH₄)₄, is presented and characterized by a combination of in situ synchrotron radiation powder X-ray diffraction, thermal analysis, and vibrational and NMR spectroscopy. The title compound, KSc(BH₄)₄, forms at ambient conditions in ball milled mixtures of potassium borohydride and ScCl₃ together with a new ternary chloride K₃ScCl₆, which is also structurally characterized. This indicates that the formation of KSc(BH₄)₄ differs from a simple metathesis reaction, and the highest scandium borohydride yield (~31 mol %) can be obtained with a reactant ratio KBH₄:ScCl₃ of 2:1. KSc(BH₄)₄ crystallizes in the orthorhombic crystal system, a = 11.856(5), b = 7.800(3), c = 10.126(6) Ã…, V = 936.4(8) Ã…³ at RT, with the space group symmetry Pnma. KSc(BH₄)₄ has a BaSO₄ type structure where the BH₄ tetrahedra take the oxygen positions. Regarding the packing of cations, K⁺, and complex anions, [Sc(BH₄)₄]^−, the structure of KSc(BH₄)₄ can be seen as a distorted variant of orthorhombic neptunium, Np, metal. Thermal expansion of KSc(BH₄)₄ in the temperature range RT to 405 K is anisotropic, and the lattice parameter b shows strong nonlinearity upon approaching the melting temperature. The vibrational and NMR spectra are consistent with the structural model, and previous investigations of the related compounds ASc(BH₄)₄ with A = Li, Na. KSc(BH₄)₄ is stable from RT up to ~405 K, where the compound melts and then releases hydrogen in two rapid steps approximately at 460−500 K and 510−590 K. The hydrogen release involves the formation of KBH₄, which reacts with K₃ScCl₆ and forms a solid solution, K(BH₄)_1−xCl_x. The ternary potassium scandium chloride K₃ScCl₆ observed in all samples has a monoclinic structure at room temperature, P2₁/a, a = 12.729(3), b = 7.367(2), c = 12.825(3) Ã…, β = 109.22(2)°, V = 1135.6(4) Ã…³, which is isostructural to K₃MoCl₆. The monoclinic polymorph transforms to cubic at 635 K, a = 10.694 Ã… (based on diffraction data measured at 769 K), which is isostructural to the high temperature phase of K₃YCl₆.

A combination of in situ synchrotron powder diffraction, energy minimization (DFT), and Raman and infrared spectroscopy confirmed porous interpenetrated 3D-framework structures of recently discovered alkali-metal−zinc borohydrides, AZn₂(BH₄)₅ (A = Li, Na). In the less zinc rich NaZn(BH₄)₃ the 3D-framework structural model has been confirmed but with a slightly modified description giving an isolated triangular anion, [Zn(BH₄)₃]^−, rather than a 1D anionic chain, {[Zn(BH₄)₃]_n}^n−. Another polymorph of NaZn(BH₄)₃, isostructural to a new compound, LiZn(BH₄)₃, is proposed by energy minimization. Both compounds, the new NaZn(BH₄)₃ polymorph and LiZn(BH₄)₃, are, however, not observed experimentally at ambient pressure and in the temperature range of 100−400 K. The alkali-metal−zinc borohydride NaZn(BH₄)₃ containing the triangular anion [Zn(BH₄)₃]^− is an equivalent of recently characterized alkali-metal−scandium borohydrides NaSc(BH₄)₄ and LiSc(BH₄)₄ based on the tetrahedral [Sc(BH₄)₄]^− complex anion.

The new double-cation Al-Li-borohydride is an attractive candidate material for hydrogen storage due to a very low hydrogen desorption temperature (~70 °C) combined with a high hydrogen density (17.2 wt %). It was synthesised by high-energy ball milling of AlCl₃ and LiBH₄. The structure of the compound was determined from image-plate synchrotron powder diffraction supported by DFT calculations. The material shows a unique 3D framework structure within the borohydrides (space group=P-43n, a=11.3640(3) Å). The unexpected composition Al₃Li₄(BH₄)₁₃ can be rationalized on the basis of a complex cation [(BH₄)Li₄]³⁺ and a complex anion [Al(BH₄)₄]^-. The refinements from synchrotron powder diffraction of different samples revealed the presence of limited amounts of chloride ions replacing the borohydride on one site. In situ Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal desorption measurements were used to study the decomposition pathway of the compound. Al-Li-borohydride decomposes at ~70 °C, forming LiBH₄. The high mass loss of about 20 % during the decomposition indicates the release of not only hydrogen but also diborane.

Inorganic borohydrides are actively studied in view of potential hydrogen storage applications. These compounds can be obtained by a variety of reactions ranging from high temperature reactions of the elements to exchange reactions in solution or in solid state. Different approaches will be discussed and compared.

A new alkaline transition-metal borohydride, NaSc(BH₄)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(BH₄)₄ forms at ambient conditions in ball-milled mixtures of sodium borohydride and ScCl₃. A new ternary chloride Na₃ScCl₆ (P2₁/n, a = 6.7375(3) Ã…, b = 7.1567(3) Ã…, c = 9.9316(5) Ã…, β = 90.491(3)°, V = 478.87(4) Ã…³), isostructural to Na₃TiCl₆, was identified as an additional phase in all samples. This indicates that the formation of NaSc(BH₄)₄ differs from a simple metathesis reaction, and the highest scandium borohydride yield (22 wt %) was obtained with a reactant ratio of ScCl₃/NaBH₄ of 1:2. NaSc(BH₄)₄ crystallizes in the orthorhombic crystal system with the space group symmetry Cmcm (a = 8.170(2) Ã…, b = 11.875(3) Ã…, c = 9.018(2) Ã…, V = 874.9(3) Ã…³). The structure of NaSc(BH₄)₄ consists of isolated homoleptic scandium tetraborohydride anions, [Sc(BH₄)₄]^–, located inside slightly distorted trigonal Na₆ prisms (each second prism is empty, triangular angles of 55.5 and 69.1°). The experimental results show that each Sc³⁺ is tetrahedrally surrounded by four BH₄ tetrahedra with a 12-fold coordination of H to Sc, while Na⁺ is surrounded by six BH₄ tetrahedra in a quite regular octahedral coordination with a (6 + 12)-fold coordination of H to Na. The packing of Na⁺ cations and [Sc(BH₄)₄]^– anions in NaSc(BH₄)₄ is a deformation variant of the hexagonal NiAs structure type. NaSc(BH₄)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(BH₄)₄ between RT and 408 K is anisotropic, and lattice parameter b shows strong anomaly close to the melting temperature.

Pages 9003−9007. The author improved the information in the CIF file in Supporting Information. The manuscript was published on the Web on April 9, 2009 (ASAP) and in print (Volume 113, Issue 20). The correct version was published on the Web on July 14, 2009.

The first crystal structure of a 3d-metal borohydride is presented.Solvent-free homoleptic manganese borohydride Mn(BH₄)₂ forms at ambient conditions in ball-milled mixtures of alkali metal borohydrides and MnCl₂. It crystallizes in the trigonal crystal system with the space group symmetry P3₁12 and is stable from 90 to 450 K, where the compound melts. Thermal expansion of Mn(BH₄)₂ between 90 and 400 K is highly anisotropic and strongly nonuniform. The structure of Mn(BH₄)₂ shows interesting similarity to α-Mg(BH₄)₂: the two structures are made of similar layers L with the composition M₄(BH₄)₁₀ per cell. The layers are stacked along the c-axis, and rotated by 120° by the 3₁ axis in Mn(BH₄)₂ and by 60° by the 61 axis in α-Mg(BH₄)₂. Three identical layers are stacked along one unit cell vector c in Mn(BH₄)₂, while six layers are stacked in α-Mg(BH₄)₂. In Mn(BH₄)₂ the layers L are connected directly, and share atoms. In α-Mg(BH₄)₂ the layers L are intercalated by a thin layer L', which contains one Mg atom per layer per cell. The layer L is chiral, and both borohydrides crystallize in chiral space groups. Similar to α-Mg(BH₄)₂, the structure of Mn(BH₄)₂ is not densely packed and contains isolated voids with the estimated volume of 21 Ã…³ each, which occupy in total 6% of the space. The resemblance between Mn(BH₄)₂ and α-Mg(BH₄)₂ is also reflected in their Raman and infrared spectra.

Geometry of [Mg(BH₄)₄] units in R-Mg(BH₄)₂, coordination of Mg₂ atom is given as an example. Two nearly planar BH₂-Mg-H₂B fragments are situated at nearly 90° dihedral angle. The shortest H · · · H distances are highlighted in green.

LiSc(BH₄)₄ has been prepared by ball milling of LiBH₄ and ScCl₃. Vibrational spectroscopy indicates the presence of discrete Sc(BH₄)₄^− ions. DFT calculations of this isolated complex ion confirm that it is a stable complex, and the calculated vibrational spectra agree well with the experimental ones. The four BH₄^− groups are oriented with a tilted plane of three hydrogen atoms directed to the central Sc ion, resulting in a global 8 + 4 coordination. The crystal structure obtained by high-resolution synchrotron powder diffraction reveals a tetragonal unit cell with a = 6.076 Ã… and c = 12.034 Ã… (space group P-42c). The local structure of the Sc(BH₄)₄^− complex is refined as a distorted form of the theoretical structure. The Li ions are found to be disordered along the z axis.

Unexpected structural complexity: Well-crystallized Mg(BH₄)₂ powder is obtained, allowing the structure to be determined from synchrotron X-ray and neutron diffraction data. Mg(BH₄)₂ is a novel and remarkably complex three-dimensional framework in which each Mg²⁺ ion (blue) is tetrahedrally coordinated by four [BH₄]^- tetrahedra (B red, H gray; see picture).

The incorporation of enantiopure 1-amino-2,3-propanediol as a subcomponent into a dicopper double helicate resulted in perfect chiral induction of the helicate's twist. DFT calculations allowed the determination of the helicity of the complex in solution. The same helical induction, in which S amines induced a Λ helical twist, was observed in the solid state by X-ray crystallography. Electronic structure calculations also revealed that the unusual deep green color of this class of complexes was due to a metal-to-ligand charge transfer excitation, in which the excited state possesses a valence delocalized Cu₂³⁺ core. The use of a racemic amine subcomponent resulted in the formation of a dynamic library of six diastereomeric pairs of enantiomers. Surprisingly, this library converted into a single pair of enantiomers during crystallization. We were able to observe this process reverse upon redissolution, as initial ligand exchange was followed by covalent imine metathesis.