2 H magic-angle spinning NMR and powder diffraction study of deuterated paramagnetic copper(II) glycinato complexes. Information on crystallographic symmetries, stereo-isomerism, and molecular mobility available from ssNMR spectra

Abstract

Effects of stereochemistry, polymorphism, crystal packing, and solid phase mobility on the 2H magic-angle spinning (MAS) NMR spectra of the paramagnetic Cu(II) glycinato complexes have been investigated. The reliability of information obtained from the spectra, such as symmetry relations within a molecule, number of chemical sites or molecules found in the asymmetric units, was confirmed by previously published X-ray crystal and molecular structures. From the 2H MAS spectra, complemented with powder diffractograms of the synthetized bis(glycinato-d4)copper(II) complexes, we could identify three solid phases, namely the cis aqua and non-aqua forms and the trans non-aqua crystals. A fourth sample was identified as octahedral copper(II) complex chain with bidentate glycine and NO3 ligands in the octahedral building units. Correlations between the sign and magnitude of the observed paramagnetic shifts and the number of bonds and/or the dihedral angles connecting the actual 2H nucleus and the paramagnetic center, useful in structural assignments, were revealed. The agreement of the 2H MAS NMR spectral information with the available crystal diffraction data forecast their applicability in NMR crystallographic works too.