Short-Lived Trace Gases in the Surface Ocean and the Atmosphere

The two-way exchange of trace gases between the ocean and the atmosphere is important for both the chemistry and physics of the atmosphere and the biogeochemistry of the oceans, including the global cycling of elements. Here we review these exchanges and their importance for a range of gases whose lifetimes are generally short compared to the main greenhouse gases and which are, in most cases, more reactive than them. Gases considered include sulphur and related compounds, organohalogens, non-methane hydrocarbons, ozone, ammonia and related compounds, hydrogen and carbon monoxide. Finally, we stress the interactivity of the system, the importance of process understanding for modeling, the need for more extensive field measurements and their better seasonal coverage, the importance of inter-calibration exercises and finally the need to show the importance of air-sea exchanges for global cycling and how the field fits into the broader context of Earth System Science

If a template fits...: Case studies in morphological cliticization

One of the most pressing questions faced by linguistic theory in general, and in particular by any account of dialect variation within the Principles and Parameters (or any other) framework, is the division of labour between syntax and morphology. Previous analyses of clitic phenomena, for example, have tended to opt for one extreme position or another: either clitics are essentially syntactic, which inevitably contributes to the proliferation of functional categories, or they are purely morphological, in which case we lose some of the explicative value of X' structures. This study follows an approach which attempts to reconcile these two extremes by recognizing that both modules may play a role in different cases of cliticization. Since we believe in working from empirical data rather than from theoretical assumptions about the nature of cliticisation, we will begin with a presentation of a range of Romance facts which involve the behaviour of pronominal clitics in nonstandard varieties of Spanish, as well as Milanese, Portuguese and Franco-ontarian. For each case, it will be shown that a syntactic analysis of the clitic facts in question is either impossible or highly undesirable. In this light, we will conclude by suggesting how morphological templates could better account for the clitic facts in these cases

Is π-donation the only way? Unprecedented unsaturated Ru(II) species devoid of π-donor ligands

Reaction of RuHX(CO)L2 (L = PtBu2Me) with tBuLi in pentane or toluene at -40°C gives Ru(H)2(CO)L2 as a reactive and thermolabile square-pyramidal species with inequivalent hydrides (one apical). This molecule forms 1:1 adducts with N2, H2, PH2Ph, PHPh2 or PHCy2, and forms Ru(H)2(CO)2L2, then Ru(CO)3L2 with CO. Oxidative addition of the H-C bond of HC2Ph, the H-Si bonds of SiPh2H2 and SiMe3H and the H-O bond of H2O occurs with elimination of H2, to give RuH(C2Ph)(CO)L2, RuH(SiR3)(CO)L2 and RuH(OH)(CO)L2, respectively. Ru(H)2(CO)L2 reacts with MeI to give RuMeI(CO)L2 and RuHI(CO)L2. Above -40°C, Ru(H)2(CO)L2 hydrogenates isobutylene and subsequently metallates one tBu group of its phosphine, to give RuH(CO)L(P∼C). This strained molecule reacts with arenes to give RuH(aryl)(CO)L2. Reaction of RuHCl(CO)L2 with PhLi provides an alternative synthesis of RuHPh(CO)L2, which rapidly ( ∼2 h) exchanges its H and Ph groups with C6D6 or with toluene. Reaction of RuHPh(CO)L2 with CO gives the much less reactive RuH(Ph)(CO)2L2, while RuHPh(CO)L2 reacts with MeI to give RuMeI(CO)L2 and with EtBr to give first Ru(Et)Br(CO)L2, then RuHBr(CO)L2 and ethylene. N-chlorosuccinimide converts RuHPh(CO)L2 into RuClPh(CO)L2. On a timescale of 2 days, RuH(aryl)(CO)L2, in arene solvent, rearranges to Ru(η6-arene)(CO)L and free L. The structural and electronic properties of the family of unsaturated RuXH(CO)(PH3)2 (X = H, SiH3, CCH, F, Cl, Br, OH, OMe) complexes have been analyzed by core potential ab initio methods at the MP2 level. The preferred structure for each member of this family is calculated to be square-pyramidal with the strongest σ-donor ligand (H or SiH3) at the apical site. Powerful σ-donating groups (i.e., ligands with a strong trans influence: H or SiR3) are found to be very efficient at compensating the electron deficiency at the metal. A π-donating ligand occupies a basal site, trans to the CO group. Due to the lack of a low-lying empty metal dπ orbital (i.e., the molecule is a sigma Lewis acid), π effects are weaker at stabilizing the unsaturation: a push-pull interaction involving the p lone pair(s) of X, the occupied d metal orbital and the π* co orbitals constitutes an additional, but secondary, stabilizing factor. This explains why Ru(H)2(CO)L2 and RuH(SiR3)(CO)L2 are both observable species. The calculated Ru-N bond dissociation energy of RuXH(NH3)(CO)(PH3)2 confirms the dominant role of the σ-donation of the ligands, especially that of the ligand trans to NH3. Thus, compounds of the type RuH(X)(CO)(PR3)2 are better regarded as primarily 'σ-stabilized' 16-electron species whose properties are then finely tuned by π effects.</p