LiAl x Mn 1Ϫx O 2 and LiCr x Mn 1Ϫx O 2 compounds (x Յ 0.10) with an ␣-NaFeO 2 layer-type crystal structure have been prepared by a high temperature solid-state route. The compounds are well ordered with Al or Cr sharing the Mn sites and no detectable cation mixing between Mn and Li layers. Both Al-and Cr-substituted materials cycled between 4.4 and 2.0 V in Li cells at 55ЊC show high stability of capacity. However the Al-substituted materials undergo a structural transformation to a spinel-type phase, accompanied by evolution of the discharge voltage curve to a two-plateau profile. Materials modified with small amounts of Cr show a different evolution of the discharge voltage. X-ray diffraction data for cycled LiCr x Mn 1Ϫx O 2 cathodes show that these compounds do not undergo significant transformation to spinel on cycling, but retain a hexagonal structure established on first charge.

Lithium manganese oxides, and in particular the spinel-structured LiMn 2 O 4 , have been investigated as potential active cathode materials for lithium ion batteries. Recently both orthorhombic and monoclinic LiMnO 2 have attracted considerable attention. It has been reported that Al doping allows the preparation of monoclinic LiAl x Mn 1−x O 2 under suitable reaction conditions, and furthermore improves the capacity retention of both o-LiAl x Mn 1−x O 2 and m-LiAl x Mn 1−x O 2 . The aim of this study was to elucidate the structural effects of Al doping with particular attention to the surface properties of the material. X-ray diffraction data reveal that Al induces monoclinic stacking faults in orthorhombic LiAl x Mn 1−x O 2 and at Al contents of ~5% the preferred cation ordering becomes that of monoclinic LiAl x Mn 1−x O 2 . X-ray photoelectron spectroscopy measurements show that the Al is homogeneously incorporated throughout the grains up to its solubility limit, and no surface enrichment of Al is observed. The XPS data indicate that Mn in the near-surface region of the material is predominantly present in its Y3 oxidation state, even when annealed to temperatures of up to 250 °C.

Electrospray ionization mass spectrometry shows arylstibonic acids, p-XC6H4SbO3H2 (X = methyl, nitro, or chloro), and 1-naphthylstibonic acid exist in MeCN as dodecanuclear aggregates [H8(RSb)12O28]. With KOH or NaOH these form polyoxometalate ions [M2H8(RSb)12O30]2− (M = K or Na) with a hexagonal antiprismatic array of the Sb atoms, as shown by X-ray crystallographic structures for three new examples. There is one firmly encapsulated 10-coordinate M+ ion within an inorganic 12-crown-6 moiety {Sb6O6} in the hexagonal channel and one six-coordinate M+.

The structure of metallurgical-or smelter-grade aluminas (MGAs) is complex and poorly understood. Ultrahigh-field solid-state 27 Al NMR results on industrial as well as on laboratory-prepared aluminas are discussed in relation to XRD results. It is demonstrated that high-field NMR can effectively be used to quantify the proportion of the thermodynamically stable alpha-alumina phase in these materials. The results demonstrate that 27 Al NMR is a vital adjunct to XRD methods to quantify the transition alumina phases that invariably dominate the MGAs. The nature of the disorder in these materials, determined by 27 Al NMR, is also compared with literature data, such as XANES and EXAFS studies, on typical laboratory-prepared materials. The utility of 27 Al NMR studies to provide new insight into the structural complexity of metallurgical aluminas is shown.Résumé : La structure des alumines de qualité métallurgique (AQM) ou pour électrolyse est complexe et mal comprise. Opérant à champ élevé et à l'état solide, on a déterminé les spectres RMN du 27 Al d'alumines industrielles et d'autres préparées en laboratoire et on discute de ces spectres en relation avec les résultats obtenus par diffraction des rayons X (DRX). On a démontré que la RMN à champ élevé peut effectivement être utilisée pour quantifier la proportion de la phase thermodynamiquement stable d'alumine alpha qui est présente dans ces matériaux. Les résultats démontrent que la RMN du 27 Al est une addition absolument nécessaire aux méthodes de DRX pour quantifier les phases d'alumines de transition qui dominent invariablement les AQM. On a aussi comparé la nature du désordre dans ces matériaux, telle que déterminée par RMN du 27 Al, avec les résultats déjà publiés dans la littérature et obtenus par des études à l'aide de la spectroscopie d'absorption X de type XANES ou EXAFS sur des matériaux typiques préparés en laboratoire. On démontre donc l'utilité de la RMN du 27 Al à fournir de nouvelles indications sur la complexité structurale des alumines métallurgiques.

The lithium salt of p-tolylstibonic acid contains the anion [LiH 3 (p-MeC 6 H 4 Sb) 12 O 28 ] 4− , in which the Li + is fully enclosed within an {Sb 12 O 28 } cage with γ Keggin ion geometry; the idealized overall formula is Li 5 [LiH 3 (p-MeC 6 H 4 Sb) 12 O 28 ]Br·18H 2 O. In contrast, Ba 2+ induces the formation of the unprecedented {Sb 14 O 34 } bowl-shaped polyoxostibonate [BaH 10 (p-MeC 6 H 4 Sb) 14 O 34 ]·4H 2 O. Compounds were characterized by single-crystal X-ray crystallography and by ESI-MS. ■ INTRODUCTIONWe have recently reported the structures of sodium and potassium salts of arylstibonic acids, which for several different e x a m p l e s r e v e a l e d p o l y o x o s t i b o n a t e a n i o n s [M 2 H 10−x (RSb) 12 O 30 ] x− (M = Na, K) with a distortedhexagonal-antiprismatic array of Sb atoms and with the M cations attached in two different sites to framework O atoms within the hexagonal channel. 1,2 This structural arrangement is conserved for a variety of aryl R groups, crystallized with several different cations. 3 ESI-MS studies showed that the cluster units retained their integrity in MeCN solution. 1,2 Recently, other polyoxometalates incorporating organoantimony have been described, particularly from the groups of Beckmann 4 and Baskar. 5 We herein demonstrate that the size of the cation is important in templating the polyoxometalate formation by showing that the smaller Li + provides an Sb 12 species with a more closed geometry, while the larger Ba 2+ gives a more open Sb 14 framework. Cronin et al. have recently reviewed 6 the importance of cations (mainly organic ones) in controlling the synthesis of molybdenum and tungsten polyoxometalates, and the present work extends this concept to polyoxostibonates. As an interesting historical note, in 1922, Schmidt 7 noted that arylstibonic acids showed different neutralization behavior with LiOH compared to that with NaOH or KOH. Only now has the reason for this become apparent. ■ EXPERIMENTAL SECTIONp-Tolylstibonic acid was prepared using the method of Doak and Steinman 8 and freed from Na + cations as described earlier. 2 ESI-MS was carried out on a Bruker MicrOTOF instrument, operating under standard conditions in negative ion mode, with samples made up in MeCN immediately before infusion. Assignment of ions was aided by matching the characteristic patterns generated by the 121 Sb (57%) and 123 Sb (42%) isotopes. Peaks are reported as the m/z values with the greatest intensity in the isotopic envelope. EDAX measurements on single crystals were performed on a Hitachi S-4700 field emission scanning electron microscope. The reported compounds do not melt at <330°C but rather undergo apparent evolution of water followed by gradual darkening. Yields are not quoted for the identified products, since these are hard to quantify. The initial powders represent essentially quantitative recovery of the solids added but are mixtures of species (as shown by ESI-MS) and have an unknown level of solvent incorporation even after drying in vacuo over P 2 O 5...