engleski

Solid-State NMR Study of Paramagnetic Bis(alaninato-κ2N, O)copper(II) and Bis(1-amino(cyclo)alkane-1-carboxylato-κ2N, O)copper(II) Complexes : Reflection of Stereoisomerism and Molecular Mobility in 13C and 2H Fast Magic Angle Spinning Spectra

Solid-state stereochemistry and mobility of paramagnetic copper(II) complexes formed by aliphatic amino acids (L-alanine, D, L-alanine, 1-amino-2-methyl-alanine) and 1-amino(cyclo)alkane-1-carboxylic acids (alkane = propane, butane, pentane, hexane) as bidentate ligands has been studied by 13C and 2H solid-state fast magic angle spinning (MAS) NMR spectroscopy. We examined the prospective method to characterize solid-state paramagnetic compounds in a routine way. Both 13C and 2H MAS spectra can distinguish D, L and L, L diastereomers of natural and polydeuterated bis([Dn]alaninato)copper(II) (n = 0, 2, 8) complexes with axial and/or equatorial methyl positions (conformations) primarily due to different Fermi-contact (FC) contributions. The three-bond hyperfine couplings clearly show Karplus-like dependence on the torsional angles which turned out to be a useful assignment aid. Density functional theory calculations of the FC term and crystal structures were also used to aid the final assignments. The correlations obtained for bis(alaninato-κ2N, O)copper(II) complexes were successfully used to characterize other complexes. The usefulness of the 2H MAS spectra of the deuterated complexes was underlined. Even the spectra of the easily exchangeable amine protons contained essential stereochemical information. In the case of a dimer structure of bis(1-aminohexane-1-carboxylato-κ2N, O)copper(II) both the 13C and 2H resolutions were good enough to confirm the presence of the cis and trans forms in the asymmetric unit. With regard to the internal solid-state motions in the crystal lattice, the obtained quadrupolar tensor parameters were similar for the D, L- and L, L-alaninato isomers and also for the cis–trans forms suggesting similar crystal packing effects, static amine deuterons involved in hydrogen bonding, and fast rotating methyl groups.

Stereoisomerism; ssNMR spectroscopy; 13C and 2H fast-MAS; paramagnetic Cu complexes

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