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ssNMR Characterization of Paramagnetic Bis(L-valinato)copper(II) Stereoisomers. Effect of Conformational Disorder and Molecular Mobility on 13C and 2H Very-fast MAS Spectra

The solid-state NMR spectra of carbon and deuteron atoms in paramagnetic anhydrous trans bis(L-valinato)copper(II) and cis aquabis(L-valinato)copper(II) complexes have been obtained. Under the very-fast MAS conditions [1] both the 13C and 2H MAS spectra were well enough resolved to allow the easy distinction between trans and cis stereoisomers. The conformational disorder observed earlier in the X-ray structure of the cis-isomer [2] was reflected in the 13C and 2H MAS spectra too. Variable temperature 2H MAS spectra of differently ligand-deuterated species, that is, the copper(II) complexes with L-valine-d2, L-valine-d8, and L-valine-d10, suggested the dynamic nature of this disorder in the aqua cis-isomer and confirmed static ND2 deuterons in the anhydrous trans-isomer. Quantum chemical DFT/B3LYP calculations of the 13C hyperfine (Fermi-contact) shifts of the paramagnetic term were useful as assignment aids in the interpretation of 13C MAS spectra. [1] N.P. Wrickramashinghe, M.A. Shaibet, and Y. Ishii, J. Phys. Chem. B. Letters, 2007, 111, 9693-9696. [2] M. Marković, N. Judaš, J. Sabolović, Inorg. Chem. 2011, 50, 3632–3644.

solid-state NMR; valine; copper; Very-fast MAS Spectra

Napomena: Predavanje je održao prof. dr. sc. Szalontai.