Charge density analysis reveals multi-centre bonds in the cluster, hydrogen bridges in the ammonia network, and the dihydrogen bond between H(delta-) and H(delta+); all observed in one compound, [Li(NH3)4]2B6H6.2NH3.

Single phase samples of lithium-doped β-rhombohedral boron were synthesised by different high temperature routes. Both single crystals and crystalline powders were obtained. Characterisation was done by electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. 653According to the crystal structure determination based on single crystal and powder data, the phase investigated is LiB ϳ10 . Depending on the synthesis route, LiB ϳ10 was found to form a compound with composition Li 30 B 309 . Further lithium intercalation is possible.

Metathetic solid-state reactions of alkaline earth perovskite zirconates (AZrO3, A = Ca, Sr, Ba) and lead sulfate (PbSO4) result in the relatively quick formation of perovskite PbZrO3 and the corresponding alkaline earth sulfate ASO4 at temperatures as low as 1023 K. The product can be described as a composite dispersion of small (<300 nm) particles of PbZrO3 on larger crystals of the alkaline earth sulfates. The solid-state reaction at 973 K between ZrO2, PbSO4, and K2CO3 followed by washing in water to remove K2SO4 provides a quick route to submicron (<1 μm) PbZrO3 powders starting from inexpensive precursors. In all the reactions, we believe the driving force to be the high enthalpy of formation of ASO4 or K2SO4. The reactions presented here provide proof of concept for the preparation of a number of important polar lead-based perovskite phases under relatively mild conditions:  (i) as composites, (ii) as small particles, and (iii) possibly as porous monoliths.

Recently, we demonstrated a very general route to monolithic macroporous materials prepared without the use of templates (Rajamathi et al. J. Mater. Chem. 2001, 11, 2489). The route involves finding a precursor containing two metals, A and B, whose oxides are largely immiscible. Firing of the precursor followed by suitable sintering results in a monolith from which one of the oxide phases can be chemically leached out to yield a macroporous mass of the other oxide phase. The metals A and B that we employed in the demonstration were Ni and Zn. From the NiO−ZnO monolith that was obtained by decomposing the precursor, ZnO could be leached out at high pH to yield macroporous NiO. In the present work, we show that combustion-chemical (also called self-propagating) decomposition of a mixture of Ni and Zn nitrates with urea as a fuel yields an intimate mixture of the oxides that can be sintered and leached with alkali to form a macroporous NiO monolith. The new process that we present here thereby avoids the need for a crystalline single-source precursor. A novel and unanticipated aspect of the present work is that the combination of high temperatures and rapid quenching associated with combustion synthesis results in an intimate mixture of wurtzite ZnO and the metastable rock-salt Ni1 - x Zn x O where x is about 0.3. Leaching this monolith with alkali gives a macroporous mass of rock-salt Ni1 - x Zn x O, which upon reduction in H2/Ar forms macroporous Ni and ZnO. There are thus two stages in the process that lead to two modes of pore formation. The first is associated with leaching of ZnO by alkali. The second is associated with the reduction of porous Ni1 - x Zn x O to give porous Ni and ZnO.

Ammonia complexes of hydroborates may be potentially promising materials for ammonia storage or indirect hydrogen storage. The title compounds contain 20.04-52.23 wt % ammonia and 5.94-13.01 wt % hydrogen. They were synthesized in liquid ammonia, using (NBu4)2[B12H12] and Li2[B10H10] as starting materials. [Li(NH3)4]2[B12H12]·2NH3 (1) crystallizes in the monoclinic crystal system (space group P2(1)/c, a = 9.183(2) Å, b = 8.133(1) Å, c = 16.375 Å, β = 110.54(1)°, V = 1143.97(40) Å(3), Z = 2). The compound is a direct precursor of the hydrogen storage compound Li2[B12H12]·7NH3. Hydroborates of the heavier alkali metals were found to crystallize in the orthorhombic crystal system: Rb2[B12H12]·8NH3 (2) (space group Pnnm, a = 14.4166(6) Å, b = 7.8221(3) Å, c = 9.5792(4) Å, V = 1080.23(8) Å(3), Z = 2), Cs2[B12H12]·6NH3 (3) (space group Pbca, a = 7.7569(8) Å, b = 14.087(2) Å, c = 18.075(2) Å, V = 1974.99(30) Å(3), Z = 4), and Rb2[B10H10]·5NH3 (4) (space group Pnma, a = 13.9510(7) Å, b = 8.675(2) Å, c = 13.966(2) Å, V = 1690.2(3) Å(3), Z = 4), as determined by single crystal X-ray diffraction. The structures are discussed briefly.