23488-44-0Relevant articles and documents
Alkaline-earth metal carboxylates characterized by 43Ca and 87Sr solid-state NMR: Impact of metal-amine bonding
Burgess, Kevin M.N.,Xu, Yang,Leclerc, Matthew C.,Bryce, David L.
, p. 552 - 561 (2014/01/23)
A series of calcium and strontium complexes featuring aryl carboxylate ligands has been prepared and characterized by alkaline-earth (43Ca and 87Sr) solid-state NMR experiments in a magnetic field of 21.1 T. In the 11 compounds studied as part of this work, a range of coordination motifs are observed including nitrogen atom binding to Ca2+ and Sr 2+, a binding mode which has not been investigated previously by 43Ca or 87Sr solid-state NMR. 43Ca isotopic enrichment has enabled the full characterization of the 43Ca electric field gradient (EFG) and chemical shift tensors of the two calcium sites in calcium p-aminosalicylate (Ca(pams)), where both NMR interactions are affected by the presence of a nitrogen atom in the first coordination sphere of one of the metal sites. The 43Ca isotropic chemical shift is sensitive to the Ca-N distance as exemplified by the NMR parameters of a second form of Ca(pams) and density functional theory (DFT) calculations. Studies of the strontium analogue, Sr(pams), confirm a similar sensitivity of the 87Sr EFG tensor to the presence or absence of nitrogen in the first coordination sphere. To our knowledge, this is the first systematic 87Sr NMR study of strontium complexes featuring organic ligands. The |CQ(87Sr)| values are found to be sensitive to the coordination number about Sr2+. In general, this work has also established a larger data set of reliable experimental |CQ( 43Ca)| values which correlate well with those obtained using gauge-including projector-augmented-wave (GIPAW) DFT calculations. It is found that the use of a recently recommended quadrupole moment for 43Ca, -44.4 mbarn, improves the agreement with experimental values. This contribution lays the groundwork for the interpretation of 43Ca and 87Sr NMR spectra of more challenging systems, particularly where nitrogen-alkaline earth metal bonding is occurring.
