Synthesis and Characterisation of [Pd10(μ-CO)(μ3-CO)4(PEt3)6] and [Pd10(μ-CO)6(μ3-CO)2(μ-CNXylyl)2(PEt3)6]

The decanuclear palladium cluster compounds [Pdio(u-CO)g(^3-CO)4 (PEtglg] and [Pdio(/(-CO)g(ii3-CO)2(//-CNXyl)2(PEt3)g] (Xyl = CgH^M^- 2,6) have been synthesised and characterised by a combination of spectroscopic data and single crystal X-ray crystallographic analyses. The former has a distorted tetracapped octahedral skeletal geometry and the latter a hexacapped tetrahedral geometry. The latter is unique in cluster chemistry and the structural change induced by the addition of isocyanide represents an interesting example of the effect of the steric requirements of the isocyanide ligand influencing the total electron count and geometry of the cluster. [Pdio(/<-CO)8(/i3-CO)4(PEt3)g] reacts with SO2 to give [Pd5(/(-S02)2(p3-S02)2(PEt3)5]

Determination of the nature of the Cu coordination complexes formed in the presence of NO and NH3 within SSZ-13

Ammonia-selective catalytic reduction (NH3-SCR) using Cu zeolites is a well-established strategy for the abatement of NOx gases. Recent studies have demonstrated that Cu is particularly active when exchanged into the SSZ-13 zeolite, and its location in either the 6r or 8r renders it an excellent model system for fundamental studies. In this work, we examine the interaction of NH3-SCR relevant gases (NO and NH3) with the Cu2+ centers within the SSZ-13 structure, coupling powder diffraction (PD), X-ray absorption spectroscopy (XAFS), and density functional theory (DFT). This combined approach revealed that, upon calcination, cooling and gas exposure Cu ions tend to locate in the 8r window. After NO introduction, Cu-ions are seen to coordinate to two framework oxygens and one NO molecule, resulting in a bent Cu-nitrosyl complex with a Cu-N-O bond angle of similar to 150 degrees. Whilst Cu seems to be partially reduced/changed in coordination state, NO is partially oxidized. On exposure to NH3 while the PD data suggest the Cu2+ ion occupies a similar position, simulation and XAFS pointed toward the formation of a Jahn-Teller distorted hexaamine complex [Cu(NH3)(6)](2+) in the center of the cha cage. These results have important implications in terms of uptake and storage of these reactive gases and potentially for the mechanisms involved in the NH3-SCR process

Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing

No abstract available

Synthetic and spectroscopic studies on heterometallic clusters of platinum

This Thesis describes the synthesis and structural characterisation of a range of heterometallic cluster compounds of platinum. Chapter 1 reviews the current knowledge in this area and gives examples of the kinds of cluster compounds which have been characterised, with some emphasis on their mode of synthesis and their structural and spectroscopic characterisation. The structures of the cluster compounds are rationalised in terms of the triangular Pt3 unit which dominates the cluster chemistry of platinum. The bonding in the simplest triplatinum cluster compounds is analysed and is used as a basis for understanding the interconversion of platinum cluster compounds and the formation of heterometallic platinum-gold cluster compounds. Chapter 2 describes the synthesis and characterisation of the homometallic platinum cluster compounds which are convenient precursors for the formation of heterometallic cluster compounds. A general synthetic route to the platinum carbonyl phosphine clusters has been developed and the exchange of bridging CO and S02 ligands in this type of cluster was investigated. The synthesis of a new type of anionic 44 electron triplatinum cluster, [Pt3(μ-S02)2(μ-X)(PR3)3]¯ described. The syntheses of heterometallic clusters from the trianguloplatinum cluster compounds are reported in Chapter 3. The use of [AuPR3] as a capping fragment generates clusters with a tetrahedral Pt3Au framework. The synthesis and characterisation of two novel "sandwich" compounds are reported in which a gold or copper atom is coordinated between two parallel triplatinum units. A full single crystal X-ray crystallographic study has been carried out on each of these compounds and their geometric parameters contrasted. Chapter 4 describes the reactions of the platinum-sulphide complex [Pt2(μ-S)(CO)(PPh3)3]. This compound is found to be chemically robust. The pt-Pt bond has so far proved resistant to insertion reactions and only the ligands trans to the sulphur atom are readily exchanged. The bridging sulphido- group appears to have an extensive coordination chemistry which has lead to the synthesis of some heterometallic complexes. This property does not, as yet, provide a route into cluster formation but instead produces complexes which are aggregates of metal atoms. The application of 31P and 195Pt NMR studies to the characterisation of platinum cluster compounds is discussed in Chapter 5. The solution NMR spectra of compounds synthesised in the course of this research are described and analysed in detail. A large amount of NMR data for homometallic triplatinum clusters has been gathered and it has been possible to characterise a number of such compounds having relatively low symmetry. The heterometallic complexes described in Chapters 3 and 4 have also been characterised using NMR spectroscopy by considering the extra MPR3 fragments as perturbations on the spectra of the compounds from which they were derived. Analysis of the complex spectra obtained for such compounds was greatly assisted by the use of computer simulation techniques.</p

Theoretical studies on cluster compounds

This Thesis describes some theoretical studies on ligated and bare clusters. Chapter 1 gives a review of the two theoretical models, Tensor Surface Harmonic Theory (TSH) and Jellium Model, accounting for the electronic structures of ligated and bare clusters. The Polyhedral Skeletal Electron Pair Theory (PSEPT), which correlates the structures and electron counts (total number of valence electrons) of main group and transition metal ligated clusters, is briefly described. A structural jellium model is developed in Chapter 2 which accounts for the electronic structures of clusters using a crystal-field perturbation. The zero-order potential we derive is of central-field form, depends on the geometry of the cluster, and has a well-defined relationship to the full nuclear-electron potential. Qualitative arguments suggest that this potential produces different energy level orderings for clusters with a nucleus with large positive charge at the centre of the cluster, enabling the spherical jellium model to be applied to alkali metal clusters seeded with magnesium and zinc. Analysis of the effects of the non-spherical perturbation on the spherical jellium shell structures leads to the conclusion that for a cluster with a closed shell electronic structure a high symmetry arrangement which is approximately or precisely close packed will be preferred. It also provides a basis for rationalising those structures, which have been predicted using ab initio calculations, of clusters with incomplete shell electronic configurations In Chapter 3, the geometric conclusions derived in the structural jellium model are developed in more detail. Alkali metal clusters with closed shell electronic configurations according to the jellium model adopt geometries of high symmetry and based on the Td , Oh and Ih point groups. For high nuclearity clusters alternative high symmetry structures can occur and those which are either the most close packed or spherical are predicted to be the most stable. When the jellium closed shell "magic numbers" coincides with one of these high symmetry structures then the cluster will be particularly stable. The group theoretical consequences of the Tensor Surface Harmonic Theory are developed in Chapter 4 for[ML2]n, [ML4]n and [ML5]n clusters where either the xz and yz or x2-y2 and xy components to Lπd and Lδd do not contribute equally to the bonding. The closed shell requirements for such clusters are defined and the orbital symmetry constraints pertaining to the interconversion of conformers of these clusters are described. In Chapter 5 Stone's Tensor Surface Harmonic methodology is applied to high nuclearity transition metal carbonyl cluster compounds with 13-44 metal atoms. Two limiting bonding situations are identified and represented in terms of general electron counting rules. If the radial bonding effects predominate the clusters are characterised by 12ns+Δi valence electrons, where Δi is the characteristic electron count of the interstitial moiety. If radial and tangential bonding effects are important then the total number of valence electrons is 12ns+2(ss+si-l), where ss and si are the number of skeletal bonding molecular orbitals associated with surface (ss) and interstitial (si) moieties. Chapter 6 develops a new theoretical framework to account for the bonding in the high nuclearity ligated clusters with columnar topologies. The wave functions of columnar metal clusters can be expressed as an expansion based on the particle on the cylinder problem. This bonding analysis is applied to clusters containing columns of triangles and squares. In Chapter 7 the origin of non-bonding orbitals in molecular compounds is reviewed and analysed using general quantum mechanical considerations. A combination of the pairing theorem and a group theoretical analysis leads to a definition of the number of the non-bonding molecular orbitals in co-ordination, polyene and cluster compounds. The non-bonding molecular orbitals have been generated by defining the nodal characteristics of the relevant orbitals and evaluating the solutions under the appropriate boundary conditions. The stereochemical role of nonbonding molecular orbitals in co-ordination compounds is also discussed.</p