Introduction 1 4 F. J. Berrya and N. G. Connellyb aDepartment of Chemistry The Open University Milton Keynes UK MK7 6AA bSchool of Chemistry University of Bristol Cantock’s Close Bristol UK BS8 1TS Volume 95 of Annual Reports Section A follows the format of previous years in covering developments in inorganic chemistry both by Group and by subjects of topical interest. This year an additional chapter covers the important and expanding area of Inorganic Pharmaceuticals; in Volume 96 the chapter on Si Ge Sn and Pb will cover both the 1998 and 1999 literature. Developments in transition metal chemistry include the synthesis of the first d0 4 4 alkyne complexes (of tantalum) the first stable CuII complex with an S donor set a unique and structurally characterised alkene-containing redox pair (of RuII and RuIII) species with l -PF and l -PO bridges and a variety of distibine derivatives.Particularly remarkable given the rarity of stable mononuclear Rh(II) complexes is the characterisation of the stable cation [RhIIH(CO)(PPh 3 ) 3 ]` formed simply by the oneelectron oxidation of the well known neutral complex [RhIH(CO)(PPh 3 ) 3 ]. While these advances might by conveniently categorised under the headings of organometallic and co-ordination chemistry the blurring of such traditional borderlines continues to lead to increasingly exciting discoveries. For example the synthesis of compounds in which an organometallic fragment is positioned in the larger opening of a calix[4]- arene cavity may lead to the promotion of sterically constrained metal-centred reactions and models based on [Fe(CN) (CO)Cp]~ a classically simple organometallic complex have been used to interpret the structure and IR spectrum of the iron centre of Ni/Fe hydrogenases.Also striking is the rapidly increasing use of density functional theory to underpin so many areas of molecular transition metal chemistry. 2 In Group 13 chemistry the synergic interaction between Al3` and NO has been observed in vivo and its possible influence on Alzheimers and other age-related neurological disorders are likely to be the subject of further investigation. Reports of the first tetrahedral aluminium clusters the stability of the Ga–Ga bond to protic reagents the characterisation of In 4 O 4 [C(SiMe 3 ) 3 ] 4 which completes the tetramer series In 4 X 4 R 4 and the huge Pt195–Tl205 nuclear spin–spin coupling constant for [(NC) 5 Pt–Tl(CN)] of 71,060 Hz (which is the largest coupling constant observed between two nuclei) illustrates the diversity of main group element chemistry.The development of new multidentate ligand systems particularly chiral derivatives containing mixed nitrogen and phosphorus donor atoms demonstrates another major 1 Annu. Rep. Prog. Chem. Sect. A 1999 95 1–2 area of interest in Group 15 chemistry. An undoubted highlight of work on Group 16 elements is the observation that stirring energy can be directly converted to chemical energy when Cu 2 O acts as a mediator/catalyst for the decomposition of water to oxygen and hydrogen.Although the mechanism is not clear it seems safe to assume that we have not heard the last of this reaction. Some other fundamentally important results include the observation that c irradiation of thiosulfate acts as a source of sulfide and the characterisation of the Te 6 N 8 core in [Te 6 N 8 TeCl 4 ]. The generation of the first Xe–S bond (the first noble gas bond to a second row element) albeit in a low temperature matrix is notable. In solid state systems we have seen the synthesis and characterisation by advanced di§raction methods of many novel zeolite-like phases such as the seven- and ninering-containing aluminosilicate denoted SSZ-23. Work on other open-framework phases templated by organic species continues apace.UFOs (organically-templated uranium fluorides) have been observed and the application of combinatorial chemistry to the solid state area has been impressively exemplified by the synthesis and characterisation of SrCe 2 O 4 . Two spectacular minerals; the aluminosilicate zeolite tscho� rtnerite containing a 96-membered cage and synthetic taranakite a layered potassium aluminium phosphate hydrate with an [95Å crystallographic axis remind us of the unlimited structural variety of the natural world. The characterisation of C 36 the smallest of all carbon cage molecules together with the synthesis and characterisation of a large range of ionic fullerides and improved methods for the preparation of carbon nanotubes which are likely to play an important role in the development of new technology illustrate impressive advancements in fullerene research. Finally in this volume we say farewell to one of our Scientific Editors–Professor Neil Connelly. Neil has been at the centre of the regeneration of Annual Reports Section A which has occurred over the past eight years and it is proper that these pages record the indebtedness of the inorganic chemistry community to his dedication and enthusiasm. With Neil’s departure we shall welcome Dr Chris Jones as a Scientific Editor of Volume 96 in the knowledge that Annual Reports Section A continues to demonstrate the health and vibrancy of all areas of inorganic chemistry. 2 Annu. Rep. Prog. Chem. Sect. A 1999 95 1&ndash