Wednesday, December 28, 2005

Hiyam Journals

Chemistry - A European Journal

Volume 12, Issue 2, Pages 363-375

X-ray Diffraction and Solid-State NMR Studies of a Germanium Binuclear Complex

Luís Mafra, Filipe A. Almeida Paz, Dr. , Fa-Nian Shi, Dr., João Rocha, Prof., Tito Trindade, Dr. , Christian Fernandez, Prof., Anna Makal, Krzysztof Wozniak, Prof., Jacek Klinowski, Prof.


A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2]4 H2O (where pmida4-=N-(phosphonomethyl)iminodiacetate and C4H12N22+=piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids. We assigned the NMR resonances with the help of CH and PH internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry).

Chemistry - A European Journal
Volume 12, Issue 1, Pages 159-168

An Investigation of Lanthanum Coordination Compounds by Using Solid-State 139La NMR Spectroscopy and Relativistic Density Functional Theory (p 159-168) Mathew J. Willans, Kirk W. Feindel, Kristopher J. Ooms, Roderick E. Wasylishen


Lanthanum-139 NMR spectra of stationary samples of several solid LaIII coordination compounds have been obtained at applied magnetic fields of 11.75 and 17.60 T. The breadth and shape of the 139La NMR spectra of the central transition are dominated by the interaction between the 139La nuclear quadrupole moment and the electric field gradient (EFG) at that nucleus; however, the influence of chemical-shift anisotropy on the NMR spectra is non-negligible for the majority of the compounds investigated. Analysis of the experimental NMR spectra reveals that the 139La quadrupolar coupling constants (CQ) range from 10.0 to 35.6 MHz, the spans of the chemical-shift tensor () range from 50 to 260 ppm, and the isotropic chemical shifts (iso) range from -80 to 178 ppm. In general, there is a correlation between the magnitudes of CQ and , and iso is shown to depend on the La coordination number. Magnetic-shielding tensors, calculated by using relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) and incorporating scalar only or scalar plus spin-orbit relativistic effects, qualitatively reproduce the experimental chemical-shift tensors. In general, the inclusion of spin-orbit coupling yields results that are in better agreement with those from the experiment. The magnetic-shielding calculations and experimentally determined Euler angles can be used to predict the orientation of the chemical-shift and EFG tensors in the molecular frame. This study demonstrates that solid-state 139La NMR spectroscopy is a useful characterization method and can provide insight into the molecular structure of lanthanum coordination compounds.

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