Kinetics of reduction of aqueous hexaammineruthenium(III) ion at Pt and Au microelectrodes: electrolyte, temperature, and pressure effects.

Rate constants kel obtained by impedance spectroscopy for the reduction of Ru(NH3)6(3+) at polycrystalline Pt and Au ultramicroelectrodes depend strongly on the identity and concentration of the anion present in the order CF3SO3(-) < Cl(-) < ClO4(-), but not on the cation of the supporting electrolyte (Na(+), K(+), H(+)). For Cl(-) as the sole anion present, kel is directly proportional to the total [Cl(-)], such that kel would be zero if Cl(-) were hypothetically absent, indicating that Cl(-) is directly involved in mediation of the Ru(NH3)6(3+/2+) electron transfer. For CF3SO3(-) as the sole counterion, the dependence of kel on the total [CF3SO3(-)] is not linear, possibly because blocking of the available electrode surface becomes dominant at high triflate concentrations.

New bonding modes for boraamidinate ligands in heavy group 15 complexes: fluxional behavior of the 1:2 complexes, LiM[PhB(NtBu)2]2 (M = As, Sb, Bi).

The reactions of MCl3 with Li2[PhB(NtBu)2] in 1:1, 1:1.5, and 1:2 molar ratios in diethyl ether produced the monoboraamidinates ClM[PhB(NtBu)2] (1a, M = As; 1b, M = Sb; 1c, M = Bi), the novel 2:3 boraamidinate complexes [PhB(NtBu)2]M-micro-N(tBu)B(Ph)N(tBu)M[PhB(NtBu)2] (2b, M = Sb; 2c, M = Bi), and the bisboraamidinates LiM[PhB(NtBu)2]2 (3a, 3a.OEt2, M = As; 3b, M = Sb; 3c.

Electrochemistry and homogeneous self-exchange kinetics of the aqueous 12-tungstoaluminate(5-/6-) couple.

The effect of alkali metal (M) chloride or triflate supporting electrolytes (0.1-1.0 mol L(-1)) on the midpoint potential E(m) of the aqueous AlW12O40(5-/6-) couple in cyclic voltammetry, after correction (E(corr)) for liquid junction potentials, can be represented in terms of ionic strength according to the extended Debye-Hückel equation.

Interactions of silicate ions with zinc(II) and aluminum(III) in alkaline aqueous solution.

We present (29)Si, (27)Al, and (67)Zn NMR evidence to show that silicate ions in alkaline solution form complexes with zinc(II) (present as zincate, Zn(OH)(3)(-) or Zn(OH)(4)(2-)) and, concomitantly, with aluminate (Al(OH)(4)(-)). Zincate reacts with monomeric silicate at pH 14-15 to form [(HO)O(2)Si-O-Zn(OH)(3)](4-) and with dimeric silicate to produce [HO-SiO(2)-O-SiO(2)-O-Zn(OH)(3)](6-). The exchange of Si between these free and Zn-bound sites is immeasurably fast on the (29)Si NMR time scale.

Kinetic evidence for five-coordination in AlOH(aq)2+ ion.

Trivalent aluminum ions are important in natural bodies of water, but the structure of their coordination shell is a complex unsolved problem. In strong acid (pH < 3.0), Al(III) exists almost entirely as the octahedral Al(H2O)6(3+) ion, whereas in basic conditions (pH > 7), a tetrahedral Al(OH)(4- structure prevails.

Electrochemistry of metal phthalocyanines in organic solvents at variable pressure.

High-pressure electrochemical investigations of representative metallophthalocyanines in solution are reported. The selected systems were ZnPc, CoPc, FePc, and CoTNPc (Pc = phthalocyanine, TNPc = tetraneopentoxyphthalocyanine) in several donor solvents and (for CoTNPc) dichlorobenzene, with [Bu(4)N][ClO(4)] as supporting electrolyte and a conventional Pt electrode referred to Ag(+)(CH(3)CN)/Ag. Electrode reaction volumes deltaV(cell) for CoTNPc and ZnPc show that consecutive ring reductions result in progressive increases in electrostriction of solvent in accordance with Drude-Nernst theory.

The decamethylferrocene(+/0) electrode reaction in organic solvents at variable pressure and temperature.

Half-wave potentials E(1/2) relative to a Ag/Ag(+) electrode, mean diffusion coefficients D, and standard electrode reaction rate constants k(el) are reported for the decamethylferrocene(+/0) couple (DmFc(+/0)) in nine organic solvents at variable pressure and (for five solvents) temperature. Limited data on the ferrocene(+/0) (Fc(+/0)) and Fe(phen)(3)(3+/2+) electrode reactions are included for comparison. Although E(1/2) for DmFc(+/0) correlates only loosely with the reciprocal of the solvent dielectric constant epsilon at ambient pressure, its pressure dependence expressed as the volume of reaction Delta V(cell) is a linear function of Phi = (1/epsilon)( partial differential ln epsilon/ partial differential P)(T) (the Drude-Nernst relation).

Cation and pressure effects on the electrochemistry of 12-tungstocobaltate and 12-tungstophosphate ions in acidic aqueous solution.

The effects of supporting electrolytes and of pressure on the electrode reactions of the aqueous CoW(12)O(40)(5-/6-) couple at 25 degrees C are reported, together with limited data on PW(12)O(40)(3-)/4-) and PW(12)O(40)(4-/5-). The half-wave potentials E(1/2) for the CoW(12) couple become moderately more positive with increasing electrolyte concentration and cationic charge, and also in the sequences Li(+) approximately Na(+) < NH(4)(+) < or = H(+) < K(+) < Rb(+) < Cs(+) and Na(+) < Mg(2+) < Ca(2+) < Eu(3+). The mean diffusion coefficients for CoW(12) with the 1:1 electrolytes are independent of electrolyte concentration and rise only slightly from Li(+) to Cs(+), averaging (2.

Self-exchange reaction kinetics of metallocenes revisited: insights from the decamethylferricenium-decamethylferrocene reaction at variable pressure.

Rate constants k(ex) and volumes of activation deltaV(ex) have been obtained using (1)H NMR for the self-exchange reaction of the [(eta(5)-C(5)(CH(3))(5))(2)Fe](+) hexafluorophosphate and tetrafluoroborate with [(eta(5)-C(5)(CH(3))(5))(2)Fe] in acetone-d(6) (deltaV(ex) = -8.6 +/- 0.3 cm(3) mol(-)(1)), dichloromethane-d(2), and (semiquantitatively) in acetonitrile-d(3).

Cation-independent electron transfer between ferricyanide and ferrocyanide ions in aqueous solution.

Electron transfer between Fe(CN)(6)(3-) and Fe(CN)(6)(4-) in homogeneous aqueous solution with K(+) as the counterion normally proceeds almost exclusively by a K(+)-catalyzed pathway, but this can be suppressed, and the direct Fe(CN)(6)(3)(-)-Fe(CN)(6)(4-) electron transfer path exposed, by complexing the K(+) with crypt-2.2.2 or 18-crown-6.

Electrochemical Kinetics of Cyanometalate Complexes in Aqueous Solution at High Pressures.

For the aqueous couples Os(CN)(6)(3-/4-), Mo(CN)(8)(3-/4-), and W(CN)(8)(3-/4-), volumes of reaction DeltaV(Ag/AgCl) relative to Ag/AgCl/4.0 mol L(-)(1) KCl and volumes of activation DeltaV(el)() for the electrode reactions are reported. Values of DeltaV(Ag/AgCl) are consistent with a very small increase in the metal-carbon bond length on reduction in each case, the main component of DeltaV(Ag/AgCl) (other than that of the reference electrode) being electrostrictive solvation change.

Volume Profile for Substitution in Labile Chromium(III) Complexes: Reactions of Aqueous [Cr(Hedta)OH(2)] and [Cr(edta)](-) with Thiocyanate Ion.

A procedure is given for correcting optical absorbance measurements made at variable pressure with a le Noble-Schlott ("pillbox") cell for the inner sleeve wall thickness. With this technique, the molar volume change for the acid ionization of aqueous [Cr(Hedta)OH(2)] was found to be +5.1 +/- 0.

Kinetics of Water Exchange on the Dihydroxo-Bridged Rhodium(III) Hydrolytic Dimer.

()()Conventional (18)O isotopic labeling techniques have been used to measure the water exchange rates on the Rh(III) hydrolytic dimer [(H(2)O)(4)Rh(&mgr;-OH)(2)Rh(H(2)O)(4)](4+) at I = 1.0 M for 0.08 < [H(+)] < 0.