Introduction 1 F. J. Berry and C. J. Jones Department of Chemistry The Open University Milton Keynes UK MK7 6AA bSchool of Chemistry The University of Birmingham Birmingham UK B15 2TT In this Volume 96 of Annual Reports Section A we have continued with the format of previous years and have reviewed the highlights in inorganic chemistry of 1999 both by Group and by subjects of topical interest. Unfortunately pressure of other work has prevented two of our contributors from submitting manuscripts in time for inclusion in Volume 96 but we hope to include reports on bioinorganic chemistry and macrocyclic ligands covering 1999 literature in Volume 97. This year three new 7p series elements have been reported 293118 289116 and 285114 (also 289114). The half lives of these nuclides support the expectation that ¢lled nuclear shells might offer `islands of stability' among super-heavy elements.Developments in main group chemistry have included the synthesis of polyhydroxylated boranes such as [B12(OH)12]2 which are crossbreeds between min- erals (borates) and boron hydrides. The isolation of poly(phosphinoborane) is notable. Materials such as the polyhedral carbaalane (AlMe)8(CCH2Ph)5H and the Al12 cluster Al12R8 [R à N(SiMe3)2] are also notable. Other areas of Group 13 chemistry have also seen signi¢cant achievements we note the material Ga22[Si(SiMe3)3]8 the octasupersilyldodecaindane [(tBu3Si)8In]12 and the triple decker thallium anion in the complex [Tl3Cp2][MoCp(CO)3]. Also notable is the use of 73Ge NMRspectroscopy previously thought to be very dif¢cult as a powerful method for the characterisation of germanes.Polymeric silicon chemistry has also seen great advances with the ¢rst characterisation of (SiCl2)n and the preparation of a dendritic polysilane with thirteen silicon atoms in the longest chain. The self-assembly of ferrocenylsilane^siloxane block copolymers is also notable. An undoubted highlight of Group 16 chemistry comes with the isolation of SeCl2 in pure form for the ¢rst time. This deceptively simple result will provide ammunition in the ongoing battle to fully tap the potential of selenium to exhibit analogous chem- istry to that of its lighter congener sulfur. Though they are again on the face of it at least simple in nature the range of small oxo-based species isolated this year bears 1 DOI 10.1039/b004891g Annu.Rep.Prog. Chem. Sect.A 2000 96 1^3 10S18(C6H12NH2)6(C6H12NH)(H2O)5 contains In10S20 10¡¦ tetrahedral clusters testament to fundamental chemistry still to be done in this area. Examples include HON [Cl2O2]�¢ [IOF5]2¡¦ [ClCO]�¢ and HXeOH; the latter is especially interesting as it raises the possibility of naturally occurring xenon species. Finally in main group chemistry we note the demonstration of Xe(II)^Cl bond formation which is elegant simplicity itself but represents a quantum leap forward in noble gas chemistry. In solid state chemistry we continue to see inorganic networks templated by organic species providing numerous new and unexpected phases with the ¡érst organically templated magnesium phosphate and titanium phosphate being reported.The use of 1,2-diaminocyclohexane (DACH) as a template in the zinc phosphate system led to [H2DACH][Zn3(PO4)2(HPO4)]2H2O which contains 24-ring channels the largest yet seen in an open-framework phase. Even more remarkably groups of six DACH templates occupy each channel in such a fashion as to leave a central free space of some 8.6 D. We must also note that In sharing corners in an equivalent fashion to the connectivity in SiO2 to enclose a void space of some 70% of the unit cell volume! We also note the elegant work which has shown that [60]fullerene molecules have wave as well as particle properties thus con¡érming that quantum physics applies to large molecules as well as to atomic particles such as electrons.The use of saccharide or steroid templates for the synthesis of a large range of fullerene bis-adducts indicates the potential in this area of chemistry. Accounts of transition metal chemistry have included some reports of metal ions 2 with unusually low co-ordination numbers. Examples are provided by 2-co-ordinate Pt and Pd centres in [M{C[N(tBu)CH2]2}2] (M �� Pd Pt) 3-co-ordinate Cu(I) in a binuclear helicate and 3-co-ordinate Fe centres in the selenolate complexes [Fe(L)(m-SeAr)] [Ar �� 2,4,6-Ph3C6H2; L �� SeAr N(SiMe3)2]. Similarly in the actinide series an example of 5-co-ordinate uranium appears in a complex containing a uranyl ion co-ordinated to the three phenolate oxygens of the macrocyclic ligand [C6H2O-1-CH2OCH2-2-tBu-4]3 3¡¦.In another paper the little recognised possibilities for optical isomerism in square planar complexes have been explained with structurally characterised examples. The ¡érst example of a Cr(VI) oxo imide complex is provided by the cyclic metallosiloxane [Cr(O)(NtBu){O[Si(Ph2)O]2}5]. Six-membered metallosiloxane rings involving Mo or W were found for the ¡érst time in [M{O[Si(Ph2)O]2}2(NtBu)(L)] (M �� Mo L �� py; M �� W L �� NH tBu). The novel bridging group m4-Sb^S^Sb has been found [{Cr(Z5-C5H5)(CO)3}4(m4-Sb2S^Sb,Sb0)] which contains a in {Cr2Sb^S^SbCr2] core. The effects of ligands on the physical properties of metal ions have also been examined. In one example a ligand induced change in spin state has been observed.This is triggered by cis/trans isomerisation of a styryl group. The electrochemical properties of a metal centre can also be affected by its ligands. A particularly good example has been found in a series of copper complexes containing tripodal amine derivatives which offer N[S(3¡¦n)Nn] (n �� 1 to 3) donor atom sets. The redox potentials of the Cu2�¢/Cu�¢ couple in these compounds could be varied over a range Annu. Rep. Prog. Chem. Sect. A 2000 96,1^3 2 of 1.5 V by changing the donor atom set. Among the actinides the Th(III) complex [Th{1,4-(SitBuMe2)2C8H6}2] has been shown by EPR measurements to have a 6d1 ground state. 2B(C3H3N2)2}(CH2Ph)(CH3)(C6H5)(py)]. Novel reactions reported in 1999 4R){MeC(CH2PPh2)3}]. In the sphere of organometallic chemistry developments during 1999 include the characterisation of the ¢rst Z5-pyrazole derivatives an example being provided by [Ru(Z5-3,5-Me2C3HN2)(Z5-C5Me5)].The ¢rst Pd(IV)-aryl bond has been found in [Pd{H include alkyne insertion into the IràC bond of [Ir(OH)(àCàCàCPh2)(PiPr3)2] and a change in ketene co-ordination mode from Z2-O,C to Z2-C,C in forming [Rh(PiPr3)(Z2-OàCàCPh2-C,C)(Z5-C9H7)]. The ¢rst example of C^H bond acti- vation in a silyl complex is provided by the equilibrium between [RuH(SiMe3)(PMe3)3] and [Ru(H)2(Z2-H2CSiMe2)(PMe3)3]. Another novel reaction involves forming a P^C bond with P4. White phosphorus reacts with [Rh(R)(C2H4){MeC(CH2PPh2)3}] to add the hydrocarbyl group R to the P4 cage and insert the rhodium centre into two P^P bonds giving [Rh(Z1:Z2-P The exploitation of co-ordination chemistry in molecular self-assembly has con- tinued to be a topic of intense interest.This ¢eld has shown tremendous growth over the past few years revealing how with imagination some relatively simple co-ordination chemistry principles can be exploited to produce amazingly elaborate structures. In order to re£ect these developments the chapter on open chain polydentate ligands which appeared in earlier volumes is replaced by a chapter on `Supramolecular Co-ordination Chemistry'. This describes new examples of polynuclear structures containing up to sixteen metal atoms some involving host^guest interactions. The ¢eld has now become suf¢ciently mature that the rational design of high symmetry co-ordination clusters is possible as set out in a review in Dalton Transactions.This describes the exploitation of incommensurate symmetry interactions in the design and construction of co-ordination clusteraterials' derived from polynuclear molecular co-ordination compounds offers an intriguing complement to the longer established chemistry of the zeolites and AlPO systems. Co-ordination compounds are alsomak- ing important contributions to the study of long distance electron or energy transfer. In one example photoinduced energy transfer has been observed through a polyphenylene bridge between a Ru(II) centre and its Os(II) counterpart 42 � distant. As the study of Chemistry matures the boundaries between its traditional subject divisions are becoming increasingly diffuse. On the one hand we see the use of `organic' templates in the synthesis of mesoporous materials containing silicate or phosphate on the other we see the growing use of transition metal centres in self-assembly reactions and supramolecular chemistry. This continuing expansion of the horizons of `inorganic chemistry' provides ample evidence of the health and vitality of the discipline. 3 Annu.Rep. Prog. Chem. Sect.A 2000 96 1