engleski

Solid-State NMR Characterization of Paramagnetic Bis(L-valinato)copper(II) Stereoisomers – Effect of Conformational Disorder and Molecular Mobility on 13C and 2H Fast Magic-Angle Spinning Spectra

The solid-state 13C and 2H NMR spectra of 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, both the 13C and 2H MAS spectra were well enough resolved to allow the easy distinction between the trans and cis stereoisomers. The conformational disorder observed previously in the X-ray structure of the cis isomer was also reflected in the 13C and 2H MAS spectra. Variable-temperature 2H MAS spectra of differently deuterated ligand species, that is, the copper(II) complexes with L-[D2]valine, L-[D8]valine, and L-[D10]valine, 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 the 13C MAS spectra.

Stereoisomerism; NMR spectroscopy; Copper; Density functional calculations

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