engleski

ssNMR Study of Deuterated Paramagnetic Bis(amino acid)copper(II) Complexes. Information on Crystal Forms, Stereo-isomerism, and Molecular Mobility Available from 2H Fast-MAS Spectra

Identification of stereoisomers in paramagnetic organometallic complexes is of general interest both in liquid and solid state. In crystalline solids single-crystal diffraction is the standard method for providing molecular structure. However, solid-state NMR has much to offer the chemist because it can both supplement and complement the diffraction results. Unfortunately, NMR spectroscopy of paramagnetic compounds is often elusive since chemical shifts may change unpredictable and signals broaden beyond detection. A recently proposed solid-state NMR methodology, coined by Ishii and co-workers as very-fast MAS method [1], turned out to be advantageous for paramagnetic compounds [2]. 2H MAS spectroscopy, utilizing the quadrupolar interaction, is widely used to detect internal motions present in crystals. Concerning the resolution the 2H MAS spectroscopy offers, in diamagnetic compounds 2H chemical shielding effects are normally too small to be useful in stereochemical assignments, however, in paramagnetic compounds this is not always so. In this lecture we are going to show that the enhanced 2H chemical shift dispersion of deuterons touched by the paramagnetic effects is normally huge and thereby 2H spectra carry molecular-level information not only on the solid-state mobility but, simultaneously, also on the stereochemistry, crystalline habit, polymorphism, and hydrogen-bonds of the molecules studied. Obviously this nucleus suffers from low sensitivity, a problem that can be overcome only by the further improvement of NMR sensitivity. At the same time deuteration of the exchangeable protons (H/D) provides a convenient, though rather limited, solution. For demonstration, we will use well known simple bis(amino acidato)copper(II) complexes (glycine, alanine, valine, iso-leucine, etc.) of different deuteration degrees. [1] N.P.Wrickramashinghe, M.A.Shaibet, C.H.Jones, L.B.Casablanca, A.C. de Dios, J.S.Harwood, Y.Ishii, J.Phys.Chem., 128, 052210 (2008) [2] G.Szalontai, J.Sabolović, M.Marković, Sz.Balogh, Eur. J. Inorg. Chem., 2014, 3330-3340.

solid state NMR; magic angle spinning; Fermi contact shifts; paramagnetic; copper(II); amino acid

Prof. dr. sc. Szalontai Gábor je održao predavanje.