Concerted and stepwise proton-coupled electron transfers in aquo/hydroxo complex couples in water: oxidative electrochemistry of [Os(II)(bpy)(2)(py)(OH(2))](2+)

Successive oxidation of transition metal(II) aqua complexes (M(II)OH(2) to M(III)OH) is a domain in which proton-coupled electron transfer reactions are extremely common. The mechanism of these PCET reactions-concerted or stepwise-is an important issue in the understanding and design of natural or artificial systems catalyzing the formation of dioxygen by four-electron oxidation of water. Concerted proton-coupled electron transfer from an aqua metal(II) to a hydroxo metal(III) complex requires the close proximity of a proton-accepting group with a pK value between those of the aqua complexes. Otherwise, stepwise electron-proton or proton-electron pathways involving high-energy intermediates are followed. Concerted proton-electron pathways involving water as proton-acceptor or proton-donor group are inefficient. Cyclic voltammetry of the title complex in buffered aqueous solution and re-examination of previous results for the same complex attached to an electrode surface are used to establish these conclusions, which provide a starting point on the route to higher degrees of oxidation, such as those involved in the catalysis of water oxidation.     

The numerical integration of relative equilibrium solutions. The nonlinear Schrodinger equation

We analyse different error propagation mechanisms for conservativeand nonconservative time-integrators of nonlinear Schrödingerequations. We use a geometric approach based on interpretingwaves as relative equilibria.     

Photodissociative production of O(1S) and N(2D) from N2O in an argon matrix at 4 K

Vacuum ultraviolet photolysis of N₂O isolated in Ar matrices at 4 K gives direct luminescent evidence for the photodissociative production of both O(¹S) and N(²D). The matrix results are compared to relative atomic quantum yields measured in the gas phase.     

Absorption spectrum of BS2 at 4°K

BS₂, trapped in neon matrices at 4°K, exhibits extensive progressions in the A²Π_u ← X²Π_g and $\text{B}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}\text{← X}{}^2\text{Π}{}_{\mathrm{g}}$ systems. From these transitions, those observed in the infrared, and a reinterpretation of gas-phase data, the following molecular constants (in solid neon) are obtained for linear symmetric ¹¹BS₂ (in cm^?1):

     

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$\text{B}{}^2\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$	T0 = 24,072	$\text{ν}{}_1\text{= 516}$
$\text{A}{}^2\text{Π}{}_{\mathrm{u}}$	T0 = 13.766	$\text{ν}{}_1\text{= 506}$
	A0 = ?263	$\text{ν}{}_2\text{= 311}$
		$\text{ν}{}_3\text{= 1535}$
$\text{X}{}^2\text{Π}{}_{\mathrm{g}}$	A0 = ?440	$\text{ν}{}_1\text{= 510}$
		$\text{ν}{}_2\text{= ～120}$
		$\text{ν}{}_3\text{= 1015}$