Mohammed Alei

Magnetic Resonance Studies on Copper(II) Complex Ions in Solution. I. Temperature Dependences of the 17O NMR and Copper(II) EPR Linewidths of Cu(H2O)62

The temperature dependences of copper (II) EPR and 17O NMR spectra are analyzed in terms of a tetragonally distorted Cu(H2O)62+ ionic species in which only the equatorial water molecules form strong σ bonds to copper (II). By reconstructing the EPR spectra at temperatures in the range −10° to 100°C, the contributions to the linewidth from spin—lattice relaxation, tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin—lattice relaxation time T1e has components from both spin—rotational and Van Vleck processes. The 17O NMR linewidth is due to scalar hyperfine interaction with the copper (II) electron spin, and the spin‐exchange correlation time τe for this mechanism is determined over the same temperature range. While T1e and τe have similar temperature dependences, τe is 6–8 times smaller than T1e, suggesting that it may be related to inversion of tetragonal distortion in the complex, rather than to electron relaxation.The temperature dependences of copper (II) EPR and 17O NMR spectra are analyzed in terms of a tetragonally distorted Cu(H2O)62+ ionic species in which only the equatorial water molecules form strong σ bonds to copper (II). By reconstructing the EPR spectra at temperatures in the range −10° to 100°C, the contributions to the linewidth from spin—lattice relaxation, tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from isotropic hyperfine splitting, are separated. It is found that the spin—lattice relaxation time T1e has components from both spin—rotational and Van Vleck processes. The 17O NMR linewidth is due to scalar hyperfine interaction with the copper (II) electron spin, and the spin‐exchange correlation time τe for this mechanism is determined over the same temperature range. While T1e and τe have similar temperature dependences, τe is 6–8 times smaller than T1e, suggesting that it may be related to inversion of tetragonal distortion in th...

Magnetic‐Resonance Studies on Copper(II) Complex Ions in Solution. II. Oxygen−17 NMR and Copper(II) EPR in Aqueous Solutions of Cu(en)(H2O)42+ and Cu(en)2(H2O)22+

The temperature dependences of the 17O NMR and Cu(II) EPR spectra of solutions of the ethylenedi‐amine complex ions Cu(en)(H2O)42+ and Cu(en)2(H2O)22+ are analyzed in terms of an octahedrally coordinated structure with tetragonal distortion. It is found that the 17O NMR spectrum is broadened and shifted by Cu(en)(H2O)42+ through scalar hyperfine interaction with the copper (II) electron spin, while Cu(en)2(H2O)22+ has no effect. The Cu(II) EPR spectra of both species have linewidth contributions from spin—rotational relaxation, from tumbling of an ionic complex having an anisotropic g factor and an anisotropic hyperfine coupling constant, and from 63Cu isotropic hyperfine and 14N isotropic extrahyperfine splitting. The results are discussed in terms of the antibonding molecular‐orbital model for the B1g ground state of Cu(II) and compared with the previous study on Cu(H2O)62+.

Gas phase 13C chemical shifts and coupling constants in the deuteromethanes

13C NMR shifts and coupling constants are reported for 13CH4, 13Cl4, and a mixture of 13CH4 and 13CH3D, 13CH2D2, 13CHD3 and 13CD4. The samples were prepared by reaction f 13CO with either pure H2 or a 1:1 H2:DD2.(AIP)

Nitrogen-15 NMR of cis-diamine-platinum(II) complexes in aqueous solution

Samples were prepared and /sup 15/NMR spectra recorded for aqueous solutions of cis-(/sup 15/NH/sub 3/)/sub 2/Pt(H/sub 2/O/sub 2//sup 2 +/(1), /sup 15/N-en Pt(H/sub 2/O)/sub 2//sup 2 +/(3)(N-en = 100% /sup 15/N-labeled-ethylene-diamine), and for derivatives of 1 and 3 in which one or both of the water molecules are replaced by 100% /sup 15/N-labeled-1-methylimidazole (/sup 15/N-Me-Im). Such replacement produces a large change in both the /sup 15/N chemical shift and on the /sup 195/Pt-/sup 15/N coupling constant for the /sup 15/NH/sub 3/ or /sup 15/N-en nitrogens. At the same time, the /sup 15/N resonanes for both /sup 15/N/sub 1/ and /sup 15/N/sub 3/ of the /sup 15/N-MeIm are shifted from their positions in an aqueous solution of /sup 15/N-MeIm, and both resonances display satellites due to /sup 195/Pt-/sup 15/N coupling. These results indicate that /sup 15/N NMR is a sensitive probe for detecting interactions between cis-diamine-Pt(II)/sup 2 +/ species and imidazole-ring nitrogen in biological systems. 1 figure, 1 table.

Determination of deuterated methanes for use as atmospheric tracers

The deuterated methanes, /sup 13/CD/sub 4/ and /sup 12/CD/sub 4/, are useful as tracers for long-range (>500-km) atmospheric transport. They are easily synthesized and released. Sampling is accomplished by collecting about 330 l of air and chromatographically separating the methane fraction, which is then analyzed by mass spectrometry for the /sup 13/CD/sub 4///sup 12/CH/sub 4/ and /sup 12/CD/sub 4///sup 12/CH/sub 4/ ratios. Detection limits in air are about 7 x 10/sup -16/ STP mol m/sup -3/ for /sup 13/CD/sub 4/ and 2 x 10/sup -15/ STP mol m/sup -3/ for /sup 12/CD/sub 4/. 11 refs., 5 figs.

15N Spin Lattice Relaxation in Liquid 15NH3 and 15ND3

The spin‐lattice relaxation times (T1) for 15N in 15NH3 and 14ND3 have been determined and are presented and discussed. The magnitudes and temperature dependences of T1 for 15NH3 and 15ND3 indicate that spin‐rotational and intramolecular dipolar interactions together dominate the 15N relaxation in 15NH3. Since γD≈ 0.15 γH, the dipolar term is small compared with the spin‐rotational term in 15ND3 at room temperature. This allows one to separate the spin‐rotational and dipolar contributions in 15NH3. Values of τc, τsr, and CN are then derived from the experimental data for 15NH3 and compared with values derived in other work.

Magnetic Resonance Studies on Copper (II) Complex Ions in Solution. III. NMR and EPR in Concentrated Ethylenediamine Solutions

Measurements of the proton and 14N NMR linewidths in ethylenediamine—water solutions of Cu(II) combined with EPR studies of Cu(II) in these media demonstrate that the first sphere relaxation and residence times both make singificant contributions to the over‐all relaxation of protons and 14N by Cu(II). Moreover, the results are consistent with the view that protons and 14N both experience the Cu(II) evironment through exchange of the ethylenediamine molecule as a whole between the bulk solvent and the Cu(II) first sphere. From the temperature dependence of the Cu(II) EPR linewidth it is further concluded that the relaxation of the electron spin occurs predominantly via the spin—rotational process at higher temperatures. At lower temperatures the EPR linewidth is broadened both by tumbling of a tetragonally distorted complex with an anisotropic g factor and hyperfine coupling constant and by the same fast chemical exchange process which provides 14N and proton relaxation in ethylenediamine.

Density and Viscosity of Liquid ND3

The density and viscosity of liquid ND3 have been measured over the temperature range from +30° to −25° and compared with the density and viscosity of liquid NH3. At any given temperature, the ratio of densities ρND3/ρNH3 is 1.187± 0.001 and the ratio of viscosities ηND3/ηNH3 is 1.20± 0.01. The fact that both ratios are independent of temperature suggests that the strengths of intermolecular interactions are essentially the same in the two liquids and that the density and viscosity differences are to be attributed to differences in molecular size and mass. The density ratio indicates that the molecular volume of NH3 in the liquid is ∼ 1% larger than that of ND3 while the viscosity ratio indicates that the viscosity varies directly as M/Vm (Vm=molar volume) for these two liquids.

15N NMR shifts for imidazole and 1-methyl imidazole in CH2Cl2 relative to aqueous solution☆

Abstract The 15 N NMR frequencies for imidazole nitrogens undergo significant shifts when imidazole or 1-methyl imidazole is taken from aqueous to CH 2 Cl 2 solution. This shift is probably primarily due to strong hydrogen-bonding between 15 N 3 of imidazole and H 2 O protons in aqueous solution.