Abstract
We report the first magic-angle spinning (MAS) nuclear magnetic resonance (NMR) study on Sn(NCN). In this compound the spatially elongated (NCN)2− ion is assumed to develop two distinct forms: either cyanamide (N≡C–N2−) or carbodiimide (−N=C=N−). Our 14N MAS NMR results reveal that in Sn(NCN) the (NCN)2− groups exist exclusively in the form of symmetric carbodiimide ions with two equivalent nitrogen sites, which is in agreement with the X-ray diffraction data. The 14N quadrupolar coupling constant
|
C
Q
|
$\vert {C}_{\text{Q}}\vert $
≈ 1.1 MHz for the −N=C=N− ion in Sn(NCN) is low when compared to those observed in molecular compounds that comprise cyano-type N≡C– moieties (
|
C
Q
|
$\vert {C}_{\text{Q}}\vert $
> 3.5 MHz). This together with the information from 14N and 13C chemical shifts indicates that solid-state NMR is a powerful tool for providing atomic-level insights into anion species present in these compounds. The experimental NMR results are corroborated by high-level calculations with quantum chemistry methods.
14N, 13C, and 119Sn solid-state NMR characterization of tin(II) carbodiimide Sn(NCN)