Harold W. Dodgen

Study of Ni(II) coordination in aqueous solution by EXAFS analysis

Extended x‐ray absorption fine structure (EXAFS) spectroscopy has been applied to the study of water coordination of the Ni(II) ion in aqueous solution. High resolution x‐ray spectra were measured for Ni(NO3) ⋅6H2O salt and its 0.1M aqueous solution using a synchrotron radiation source. Analysis of the spectra by Fourier transform reveals first sphere coordination in agreement with x‐ray diffraction results. In addition, a second coordination sphere is detected and a tentative distance from the Ni(II) ion to the second sphere water molecules of 3.2±0.1 A is measured.

Chlorine‐35 NMR Study of the Shifts and Line Shapes of Some Liquid Inorganic Chlorides

The chemical shifts and linewidths of a series of 18 liquid inorganic chlorides have been measured using 35Cl broadline NMR techniques. The chemical shifts vary from 120–950 ppm downfield from the chloride ion. Assuming the mean excitation energies of these compounds are equal, a rough correlation of shift with quadrupole coupling constants is obtained for the nontransitional metal chlorides. The shifts of the transitional metal chlorides do not correlate with the quadrupole coupling constants, suggesting dπ–pπ interactions. The full linewidths at half‐maximum intensity vary from 0.15–48 G. The observed widths, corrected for viscosity and molecular dimensions, correlate reasonably well with the quadrupole coupling constants. The observed correlation times τc are about a factor of 10 shorter than those calculated with the Debye–Einstein equation. The line shapes and widths were determined using a computer program that resolved the experimental spectra in terms of overlapping Lorentzian functions.

Variable pressure and temperature 1H NMR studies on exchange mechanisms in π-allylpalladium(II) complexes

Abstract High pressure 1H NMR spectroscopy on a mixture of [Pd(2-methallyl)Cl]2 (dimer) and Pd(2-methallyl)Cl(PPh3) (monomer) in CDCl3 at 22°C gives ΔV‡ = 0 ± 2 cm3/mol. At this temperature syn-anti exchange of the allyl hydrogens in Pd(2-methallyl)Cl(PPh3) occurs, catalyzed by the complex [Pd(2-methallyl)Cl]2. To explain this ΔV‡ value we propose an overall cancelling of opposite volume contributions from the initial partial bridge cleavage of dimer and its subsequent association with monomer. At 56° C ΔV‡ is 11 ± 2 cm3/mol. At this temperature, 2-methallyl exchange between Pd(2-methallyl)Cl(PPh3) and [Pd(2-methallyl)Cl]2 occurs by a process involving dimer cleavage followed by PPh3 transfer. We propose the bridge cleavage of dimer to Pd(2-methallyl)Cl is the dominant step causing the overall positive ΔV‡ change.

Nuclear quadrupole resonance of nitrogen-14 in guanidine complexes, cyanoguanidine, and substituted ureas

Abstract The nuclear quadrupole resonance of nitrogen-14 in guanidine monohydrochloride, guanidine acetate, guanidine oxalate, guanidine monothiocyanate, guanidine sulfate, guanidine carbonate, cyanoguanidine, ethylurea and sym.-diethylurea were observed at various temperatures. The coupling constants and asymmetry parameters are interpreted in terms of the Townes and Dailey theory.

High-pressure effects on the proton nuclear magnetic resonance spectra of palladium(II) complexes of cyclic sulphides. Estimation of activation volumes for inversion about sulphur

The dynamic 1H n.m.r. spectra of the complexes trans-[PdBr2([graphic omitted]H2)2], trans-[PdCl2([graphic omitted]H2)2], and trans-[PdCl2{[graphic omitted]H2)5}2] in CHCl3 and trans-[PdCl2([graphic omitted]H2)2] in CH2Cl2 solvent have been measured for pressures up to 220 MPa. In each case a very small (0 ± 2 cm3 mol–1) volume of activation is found. These ΔV‡ values indicate no dissociative, associative, or solvent participation in the inversion process at sulphur, and substantiate the proposal that the major contribution to the entropy is the reorganizational effect on achieving ring planarity.