Torben R. Jensen

A Series of Mixed‐Metal Borohydrides

Mix and match: A novel series of alkali-metal zinc borohydrides, LiZn 2(BH 4) 5 (see picture), NaZn 2(BH 4) 5, and NaZn(BH 4) 3, with fascinating structures are presented. An interpenetrated network structure, containing a [Zn 2(BH 4) 5] -. ion, is observed for the first time for a borohydride. A three-dimensional framework containing a polymeric [{Zn(BH 4) 3} n] n- ion is also identified.

Versatile in situ powder X-ray diffraction cells for solid–gas investigations

Two multipurpose sample cells of quartz (SiO2) or sapphire (Al2O3) capillaries, developed for the study of solid–gas reactions in dosing or flow mode, are presented. They allow fast change of pressure up to 100 or 300 bar (1 bar = 100 000 Pa) and can also handle solid–liquid–gas studies.

Porous and Dense Magnesium Borohydride Frameworks: Synthesis, Stability, and Reversible Absorption of Guest Species†

A highly porous form of Mg(BH4)2 (see picture; Mg green, BH4 blue, unit cells shown in red) reversibly absorbs H2, N2, and CH2Cl2. At high pressures, this material transforms into an interpenetrated framework that has 79 % higher density than the other polymorphs. Mg(BH4)2 can act as a coordination polymer that has many similarities to metal–organic frameworks.

Thermal Polymorphism and Decomposition of Y(BH4)(3)

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 beta-Y(BH(4))(3), is discovered besides the Y(BH(4))(3) polymorph previously reported, denoted alpha-Y(BH(4))(3). beta-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) A, as compared to alpha-Y(BH(4))(3), a = 10.7445(4) A (Pa3). Beta-Y(BH(4))(3) crystallizes with a regular ReO(3)-type structure, hence the Y(3+) cations form cubes with BH(4)(-) anions located on the edges. This arrangement is a regular variant of the distorted Y(3+) cube observed in alpha-Y(BH(4))(3), which is similar to the high pressure phase of ReO(3). The new phase, beta-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 alpha- to beta-Y(BH(4))(3), at approximately 180 degrees C. Upon further heating, beta-Y(BH(4))(3) decomposes at approximately 190 degrees C to YH(3), which transforms to YH(2) at 270 degrees C. An unidentified compound is observed in the temperature range 215-280 degrees 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.

Structure and properties of complex hydride perovskite materials

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(-)←X(-) (X(-)=Cl(-), Br(-), I(-)) provides a link to the known ABX3 halides.

Eutectic melting in metal borohydrides

A series of monometallic borohydrides and borohydride eutectic mixtures have been investigated during thermal ramping by mass spectroscopy, differential scanning calorimetry, and photography. Mixtures of LiBH4-NaBH4, LiBH4-KBH4, LiBH4-Mg(BH4)2, LiBH4-Ca(BH4)2, LiBH4-Mn(BH4)2, NaBH4-KBH4, and LiBH4-NaBH4-KBH4 all displayed melting behaviour below that of the monometallic phases (up to 167 °C lower). Generally, each system behaves differently with respect to their physical behaviour upon melting. The molten phases can exhibit colour changes, bubbling and in some cases frothing, or even liquid-solid phase transitions during hydrogen release. Remarkably, the eutectic melt can also allow for hydrogen release at temperatures lower than that of the individual components. Some systems display decomposition of the borohydride in the solid-state before melting and certain hydrogen release events have also been linked to the adverse reaction of samples with impurities, usually within the starting reagents, and these may also be coupled with bubbling or frothing of the ionic melt.

Powder diffraction methods for studies of borohydride-based energy storage materials

Abstract The world today is facing increasing energy demands and a simultaneous demand for cleaner and more environmentally friendly energy technologies. Hydrogen is recognized as a possible renewable energy carrier, but its large-scale utilization is mainly hampered by insufficient hydrogen storage capabilities. In this scenario, powder diffraction has a central position as the most informative and versatile technique available in materials science. This is illustrated in the present review by synthesis, physical, chemical and structural characterisation of novel boron based hydrides for hydrogen storage. Numerous novel BH4– based materials have been investigated during the past few years and this class of materials has a fascinating structural chemistry. The experimental methods presented can be applied to a variety of other materials.

Enhanced Surface Activation of Fibronectin upon Adsorption on Hydroxyapatite

In this study the adsorption characteristics and the structure of fibronectin adsorped on hydroxyapatite (Ha) and a reference gold substrate (Au) is examined by quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) at the following concentrations: 20 microg/mL, 30 microg/mL, 40 microg/mL, 100 microg/mL, 200 microg/mL, and 500 microg/mL. The conformational changes of the fibronectin molecules upon surface binding were examined as well with monoclonal antibody directed against the cell binding-domain (CB domain) of fibronectin. The QCM-D and AFM results show that the fibronectin uptake is larger on Au as compared with Ha regardless of the protein bulk concentration used in the experiment, suggesting that the individual fibronectin molecules in general attach to the surfaces in a more unfolded configuration on Ha. Moreover the dissipation values obtained with QCM-D indicate that the individual fibronectin molecules bind in a more compact and rigid configuration on Au compared to the Ha surface. In particular the monoclonal antibody data show that the CB domain on fibronectin is more available on Ha, where such cell-recognizing abilities are more pronounced at low fibronectin surface coverage. The results demonstrate that the detailed molecular structure of fibronectin and its functional activity depend significantly on both the underlying surface chemistry as well as the fibronectin surface coverage.

Screening of metal borohydrides by mechanochemistry and diffraction.

Ay, theres the rub: The formation of cadmium-based borohydrides is screened by mechanochemical synthesis using various reactants in different ratios. Sequential in situ variable-temperature diffraction studies provide simultaneous information about composition, structure, decomposition pathways, and properties of the compounds.

Novel methods for studying lipids and lipases and their mutual interaction at interfaces. Part I. Atomic force microscopy

Mono-layers of lipids and their interaction with surface active enzymes (lipases) have been studied for more than a century. During the past decade new insight into this area has been obtained due to the development of scanning probe microscopy. This novel method provides direct microscopic information about the system in question and allows in situ investigations under near physiological conditions. In the present review the theory, experimental set-up and sample requirements of atomic force microscopy (AFM) are described. An overview of recent results is also presented with special emphasis on lipase hydrolysis and kinetics investigated in situ using AFM.