Reference LCIB-ARTICLE-2007-010doi:10.1021/cr030726oView record in Web of Science Record created on 2007-02-14, modified on 2017-05-12

Inorganic and bioinorganic solvent exchange mechanisms.

Transition metal nitrite complexes

### Background

The proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies. This trend is likely to continue because of the development of micro-analytical techniques (e.g. laser ablation, ion microprobe, femtomole-carrier gas methods, etc.) for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record (see McKibben et al. 1998). Equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems. Indeed, determination of the distribution of the stable isotopes of C-O-H-S in gases, fluids, and minerals has become a standard and extremely powerful approach in elucidating the temperatures, material fluxes, rock and fluid origins, and time scales associated with ancient and active fluid-rock interaction processes in the Earth’s crust (see Valley et al. 1986). Although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by Urey (1947), the calibration of fractionation factors has proven to be difficult. During the last four decades, a great deal of progress has been made in determining the equilibrium fractionations of 18O/16O, D/H, 13C/12C, and 34S/32S among fluid and mineral components at high temperatures (≥400°C), both from experimental exchange studies, theoretical calculations (using vibrational spectra), semi-empirical calculations (using bond-type considerations), and empirical calibrations based on natural assemblages (see references in O’Neil 1986; Kyser 1987; Criss 1991, 1999; Chacko et al., this volume). Of these, the experimental method is the most direct because it involves the least number of a priori assumptions.

Despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water-rock …

Rates and Mechanisms of Isotopic Exchange

Interaction of a predesigned molecular “clip” (4) with rigid dipyridyl bridging ligands, in acetone/water mixtures, leads to the formation of molecular rectangles (5−8) in 92−97% isolated yields via spontaneous self-assembly. Characterization was accomplished with multinuclear NMR and UV−vis spectroscopy, FAB mass spectrometry, and X-ray crystallography. The length of these metallamacrocycles ranges from 2 to 3 nm. Postmodification via non-nucleophilic counterion exchange results in enhanced structural integrity for the assemblies.

Self-assembly with postmodification: kinetically stabilized metalla-supramolecular rectangles.

A modified high‐pressure, stopped‐flow apparatus has been developed to enable kinetic experiments to be monitored spectrophotometrically to 200 MPa, with efficient mixing of the reactant solutions. This apparatus is compact, relatively inexpensive to construct, and the solutions are only exposed to inert materials, such as Kel‐F, Teflon, quartz (low‐pressure windows), and glass or Viton. The drive‐syringe pistons are propelled by a step motor housed on top of the stopped‐flow unit inside the pressure vessel, resulting in a dead time for the system of ∼10 ms at 25 °C.

Spectrophotometric stopped-flow apparatus suitable for high-pressure experiments to 200 MPa

Volumes of activation for the anation of Pd(II) substituted dien complexes by chloride ion in aqueous solution. A high pressure stopped-flow instrument for studying the kinetics of fast reactions under pressure

Activation volumes of the reactions of transition metal compounds in solution

Activation volumes for the linkage isomerization reactions of nitritopentaammine complexes of cobalt(iii), rhodium(iii) and iridium(iii) in aqueous solution

Mechanistic information from the effect of pressure on the kinetics of some anation reactions of aquopentaamminecobalt(III), -rhodium(III), and -chromium(III) ions in acidic aqueous solution

Substitution reactions of cis- and trans-bis(triethylphosphine)mesityl(bromo)platinum(II) with iodide and thiourea in methanol. Evidence for an associative mechanism

H. Kelm

Papers

Volumes of activation for the anation of Pd(II) substituted dien complexes by chloride ion in aqueous solution. A high pressure stopped-flow instrument for studying the kinetics of fast reactions under pressure

Activation volumes of the reactions of transition metal compounds in solution

Activation volumes for the linkage isomerization reactions of nitritopentaammine complexes of cobalt(iii), rhodium(iii) and iridium(iii) in aqueous solution

Mechanistic information from the effect of pressure on the kinetics of some anation reactions of aquopentaamminecobalt(III), -rhodium(III), and -chromium(III) ions in acidic aqueous solution

Substitution reactions of cis- and trans-bis(triethylphosphine)mesityl(bromo)platinum(II) with iodide and thiourea in methanol. Evidence for an associative mechanism