The preparation and crystal structures of the n = 2 Ruddlesden−Popper phases Sr2 - x Ln1+ x Mn2O7 (0 ≤ x ≤ 0.5, Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, and Er) are described. The crystal chemistry and stability of this structure is governed by the size of the lanthanide cation. Partial ordering of the Sr2+ and Ln3+ cations occurs between the two available A cation (A = Ln3+, Sr2+) sites, with the smaller lanthanides preferring the site in the rock-salt layer over that in the perovskite block. This ordering is almost complete for the small lanthanides (Tb−Er), and these ordered compounds can be prepared as single phases. Cation disorder in compounds of the larger lanthanides is accompanied by a subtle separation into two n = 2 Ruddlesden−Popper phases, which is apparent only upon detailed inspection of Rietveld refinements of the X-ray profiles. In these cases, the two-phase model is found to be superior to a single phase model with strain broadening included. For a particular lanthanide, both the ease of synthesis of single phases and the extent of cation ordering depend on the manganese oxidation state.

A wide range of structurally characterized adducts of CO2are discussed in this review, from the strongly bound, charge assisted carbamate complexes through the weaker halide and pseudo-halide complexes to the weakest possible inclusion complexes.

Magnetization and magnetotransport measurements have been used to study the composition dependence of the electronic properties of the Ruddlesden-Popper phases Sr 2 NdMn 2 O 7 and Sr 1.9 Nd 1.1 Mn 2 O 7 . Although their behaviour differs in detail, both compounds show a colossal magnetoresistance (CMR) effect (>10 000% in 14 T) in the temperature range 4.2 T /K 100. However, neither material shows a transition to a ferromagnetic state above 4.2 K, and both materials have higher resistivities (>10 3 cm for 4.2 T /K 100) than the metallic oxides previously found to show CMR. In view of the low conductivity and the absence of ferromagnetism, the CMR of these phases is not readily explained by a doubleexchange mechanism.

The synthesis and characterization of group 10 metal pincer complexes supported by a new bis(indolylphosphino)silyl ligand are described, including the synthesis of Ni, Pd, and Pt hydride species. Solution NMR and single-crystal X-ray data revealed that a significant amount of structural variability is possible for such hydride complexes, particularly in the case of Ni, where terminal Ni-H as well as complexes involving η 2 -SiH coordination are both accessible and may even coexist, in ratios dependent on factors such as the nature of additional coligands, including N 2 from the reaction atmosphere, as well as solvent and temperature. Nickel and palladium hydride complexes of this new ligand were found to exhibit divergent selectivity in the catalytic hydroboration of CO 2 with pinacolborane (HBPin). While the Pd catalyst exhibited moderate activity for CO 2 hydroboration to the formate level, the analogous Ni species exhibited unprecedented selectivity (97%) for hydroboration of CO 2 to the formaldehyde level to provide the bis(boryl)acetal PinBOCH 2 OBPin in high yield, under mild conditions. The HBPin-derived bis(boryl)acetal can be successfully isolated and utilized as a source of methylene for the formation of C−N and C−P bonds.

Why does cyanide not react destructively with the proximal iron center at the active site of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, an enzyme central to the biosynthesis of ethylene in plants? It has long been postulated that the cyanoformate anion, [NCCO2]–, forms and then decomposes to carbon dioxide and cyanide during this process. We have now isolated and crystallographically characterized this elusive anion as its tetraphenylphosphonium salt. Theoretical calculations show that cyanoformate has a very weak C–C bond and that it is thermodynamically stable only in low dielectric media. Solution stability studies have substantiated the latter result. We propose that cyanoformate shuttles the potentially toxic cyanide away from the low dielectric active site of ACC oxidase before breaking down in the higher dielectric medium of the cell.