The kinetics of oxidation of hydroxylamine by iron() have been studied spectrophotometrically. The effects of pH, reactant and product concentrations led to two experimental rate expressions. The results obtained are consistent with a mechanism dependent on the relative iron()-to-hydroxylamine concentrations; an excess of iron() gives a stoichiometry of 2 : 1 for the total reaction and N 2 O as the oxidation product, whereas at equal amounts or excess of hydroxylamine the stoichiometry reduces to 1 : 1 with N 2 as the main product . In the latter case the rate expression -The consistent mechanism identifies two pre-equilibria and the reaction of two different nitrogen-containing intermediates as the rate-determining step depending on the reactant ratios. The proposed mechanism does also involve the metal hydroxide complex Fe(OH) 2ϩ , in agreement with previous results.

The methods of preparation for Bi8(A1C14)2 and Bi6C17 have been improved and the single crystal structures for these cluster compounds re-investigated and re-interpreted. In addition, conductivity measurements and band structure calculations using the tight-binding approximation have been performed on BieC17 and related subvalent bismuth halides. -Bi,(A1C14)2 consists of isolated A1C1, anions and rather undistorted square-antiprismctic Bi2+ clusters with an average Bi-Bi distance 0f~3.10 A. Relatively short intercluster Bi-Bi contacts of 3.90 A suggest weak bonding interactions between the Big+ units. In contrast, the structure determination of Bi6C17 implies that this structure should be regarded as being composed of discrete BkZ+ clusters and a polymeric Bi"'-Cl anionic lattice including infinite, distorted A[Bi2C1$+] chains. According to the experimental and theoretical results, the Bi6X7 (X = C1, Br) family of subvalent bismuth halide compounds are anisotropic semiconductors along the crystallographic c axis. The conductivity is mediated by the onedimensional &[BizCli'] chains. These are interconnected with the Bi$+ clusters, which are acting as electron resenroirs. The related BiX (X = Br, I) family of subvalent bismuth halides are shown to be anisotropic semiconductors in the crystallographic b direction. Subvalent bismuth chloride was at first formulated as BiCl[',21, but was later crystallographically shown to actually have the stoichiometry Bi6C17 and to exhibit an unusually complex structure with isolated Bi;+ clusters and chlorobismuthate(II1) c~rnplexes[~-~]. The authors described the structure as (Bi$')2(Bi2Cl$-)(BiCl~L)4, corresponding to the over-all stoichiometry Bi6C17. The 1 : 1 BiCl compound has so far not been synthesised, and it is interesting to note the following trend in the stoichiometry of the subvalent bismuth halides that have been isolated and characterized : Bi6C17Bi6Br7 BiBrAll these compounds have been structurally characterised in the solid ~t a t e [~- '~] and the Bi6X7 (X = C1 or Br) pair found to be structurally analogous. There are two main reasons for our interest in the latter two compounds. First, Bi6CI7 has been reported to be a metallic conductor, whereas the structural and chemical analogue Bi6Br7 is claimed to be an insulator [7]. Such a difference is very surprising considering the isostructurality and chemical simi-BiI Bi71Z, Bi912 larity of the two compounds. Second, the previous structural characterisations of Bi6C17 are incomplete in the sense that the chloride positions were not refined anisotropically. In this work, the crystal structure of Bi6C17 has been redetermined, and the conductivity of a single crystal determined. The new results have then been rationalised using band structure calculations.BiBr and the three different modifications of BiI are also structurally analogous and contain one-dimensional Bi2X4 double chains bridged by metal-metal bonded chains of interstitial, formally zero-valent Bi atom^ [^,^]. The more metal-rich subvalent bismuth iodide ...

Pentabismuth(3+) tetrachlorogallate(III), (Bi(5)(3+))(GaCl(4)(-))(3), has been synthesized by reducing a BiCl(3)-GaCl(3) melt with bismuth metal and the crystal structure refined from X-ray (Cu Kalpha(1)) powder diffraction data. The structure was found to belong to space group R-3c, with the lattice parameters a = 11.871(2) Å and c = 30.101(3) Å (Z = 6). It is isostructural with the previously characterized Bi(5)(AlCl(4))(3). An attempt to synthesise the antimony analogue Sb(5)(GaCl(4))(3) by reducing a SbCl(3)-GaCl(3) mixture with gallium metal produced a black solid phase. The gallium content of this phase is consistent with the stoichiometry Sb(5)(GaCl(4))(3), and the Raman spectrum of the phase dissolved in SbCl(3)-GaCl(3) comprises strong, low-frequency bands attributable to Sb-Sb stretch vibrations in Sb(5)(3+) or another reduced antimony species. Quantum chemical analyses have been performed for the isoelectronic, trigonal pyramidal closo-clusters Sn(5)(2-), Sb(5)(3+), Tl(5)(7-), Pb(5)(2-), and Bi(5)(3+), both with extended Hückel (eH) and Hartree-Fock (HF) methods. The HF calculations were performed with and without corrections for the local electron-electron correlation using second-order Møller-Plesset perturbation theory (MP2). All theoretical results are compared and evaluted with respect to experimental cluster structures and vibrational frequencies. The results from the calculations agree well with available experimental data for the solid-state structures and vibrational spectra of these cluster ions, except for the Tl(5)(7-) ion. Isolated Tl(5)(7-) is suggested to be electronically unstable because of the high charge density. The Sb(5)(3+) cluster ion is indicated to be stable. According to the calculations, Sn(5)(2-) and Pb(5)(2-) may be described in terms of edge-localized bonds without substantial electron density between the equatorial atoms, whereas Sb(5)(3+) and Bi(5)(3+) have electron density evenly distributed over all M-M vectors. Furthermore, the theoretical results give no support for a D(3h) --> C(4v) fluxionality of these clusters.

Results from liquid X-ray scattering show that both [Ni(6)(CO)(12)](2)(-) and [Pt(6)(CO)(12)](2)(-) adopt an overall staggered ditriangular structure of D(3) symmetry in solution. Theoretical calculations show that the energy barrier of rotation is quite small, in particular for the platinum cluster. The possibilities to stabilize monotriangular carbonyl clusters of Ni and Pt in solution were also investigated. Only monotriangular [Pt(3)(CO)(6)](2)(-) can be stabilized as verified by NMR and IR spectroscopy as well as X-ray scattering. The structure is analogous to that found in the individual triangular units of [Pt(6)(CO)(12)](2)(-), and there is no unambiguous evidence for the need of additional apical CO's to stabilize [Pt(3)(CO)(6)](2)(-) in solution. Attempts to isolate the corresponding [Ni(3)(CO)(6)](2)(-) cluster instead produced the very stable [Ni(5)(CO)(12)](2)(-). Mixed solutions of the ditriangular clusters give rise to heteroclusters, whose chemistry is dominated by the facile disproportionation of the Ni(6) clusters.