A new approach to the energetics of clusters and related systems

The work described in this thesis is concerned with cluster-species and related systems, many of which are electron deficient. The term 'electron deficient' is used to describe a polynuclear species in which there are too few valence electrons to allocate a localised 2-centre 2-eleotron bond to every pair of atoms which are within normal covalent bonding distance. The bonding in these systems may be rationalised instead in terms of the relationship between the total number of skeletal electrons provided by the skeletal cluster units, and the total number of skeletal atoms. The aim of this work is to suggest new ways in which bond enthalpy contributions can be allocated to individual 2-centre links in cluster systems. In order to obtain energy terms (E) which reflect changes in bond length, (d), relationships of the form E α d(^-k)(where k=constant; 2<k≤5) are proposed. Such empirical correlations are shown to be appropriate for simple main group systems and are applied in turn to boron hydrides, borane anions, transition metal carbonyls and to complexes containing multiple metal-metal bonds. Similar relationships are used to suggest possible bond orders in some systems. Finally, the extent to which skeletal electron counting methods may be used to rationalise the bonding in boranes, carboranes, transition metal complexes and small clusters, metal π-hydrocarbon complexes and small cyclic hydrocarbons is discussed

The sting's the thing

Bees defend themselves by stinging and injecting a venom into their victims; bee venom is a complex mixture of chemicals including the polypeptide melittin which is mainly responsible for triggering the pain of the stin

Ice and Beyond: Tetrahedral Building Blocks in Crystalsa

Tetrahedral building blocks are immensely important in inorganic materials. The structure of ice is ideal for presenting this concept, combined with an introduction to hydrogen bonding. Connecting tetrahedral building blocks is then extended to polymorphs of silica

The fungus Amanita muscaria: from neurotoxins to vanadium accumulation

The fungus Amanita muscaria contains neurotoxins which account for its long-time use as a hallucinogen. In contrast, A. muscaria is also a bioaccumulator of high levels of vanadium, the reason for which is still obscur

Nature's Chemical Weapons: Beetle Defenses

The defense chemicals secreted by beetles are very diverse. They are exemplified by those of members of the families Carabidae (ground beetles) and Coccinellidae (ladybirds)

Coordination Polymers and Metal-Organic Frameworks: Structures and Applications-A Themed Issue in Honor of Professor Christoph Janiak on the Occasion of His 60th Birthday

Non

Plant toxins: poison or therapeutic?

Many plants that are classed as poisonous also have therapeutic uses, and this is illustrated using members of the Drimia and Digitalis genera which are sources of cardiac glycosides

The surprising lability of bis(2,2’:6’,2’’-terpyridine)- chromium(III) complexes

The complex [Cr(tpy)(O3SCF3)3] (tpy = 2,2′:6′,2′′-terpyridine) is readily made from [Cr(tpy)Cl3] and is a convenient precursor to [Cr(tpy)2][PF6]3 and to [Cr(tpy)(4′-(4-tolyl)tpy)][PF6]3 and [Cr(tpy)(5,5′′-Me2tpy)][PF6]3 (4′-(4-tolyl)tpy = 4′-(4-tolyl)-2,2′:6′,2′′-terpyridine; 5,5′′-Me2tpy = 5,5′′-dimethyl-2,2′:6′,2′′-terpyridine); these are the first examples of heteroleptic bis(tpy) chromium(III) complexes. The single crystal structures of 2{[Cr(tpy)2][PF6]3}·5MeCN, [Cr(tpy)(4′-(4-tolyl)tpy)][PF6]3·3MeCN and [Cr(tpy)(5,5′′-Me2tpy)][PF6]3·3MeCN have been determined. Each cation contains the expected octahedral {Cr(tpy)2}3+ unit; in all three structures, the need to accommodate three anions per cation and the solvent molecules prevents the formation of a grid-like array of cations that is typical of many lattices containing {M(tpy)2}2+ motifs. Three reversible electrochemical processes are observed for [Cr(tpy)(4′-(4-tolyl)tpy)][PF6]3 and [Cr(tpy)(5,5′′-Me2tpy)][PF6]3, consistent with those documented for [Cr(tpy)2]3+. At pH 6.36, aqueous solutions of [Cr(tpy)2][PF6]3 are stable for at least two months. However, contrary to the expectations of the d3 Cr3+ ion being a kinetically inert metal centre, the tpy ligands in [Cr(tpy)2]3+are labile in the presence of base; absorption and 1H NMR spectroscopies have been used to monitor the effects of adding NaOH to aqueous and CD3OD solutions, respectively, of the homo- and heteroleptic complexes. Ligand dissociation is also observed when [Bu4N]F is added to CD3OD solutions of the complexes, but in aqueous solution, [Cr(tpy)2][PF6]3 is stable in the presence of fluoride ion

The d(10) route to dye-sensitized solar cells: step-wise assembly of zinc(II) photosensitizers on TiO2 surfaces

Dye-sensitized solar cells have been assembled using a sequential approach: a TiO2 surface was functionalized with an anchoring ligand, followed by metallation with Zn(OAc)(2) or ZnCl2, and subsequent capping with a chromophore functionalized 2,2`:6`,2 ``-terpyridine; the DSCs exhibit surprisingly good efficiencies confirming the effectiveness of the new strategy for zinc-based DSC fabrication