¹⁴N, ¹³C, and ¹¹⁹Sn solid-state NMR characterization of tin(II) carbodiimide Sn(NCN)

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–N$^{2-}$) or carbodiimide ($^{-}$N=C=N$^{-}$). Our $^{14}$N 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 $^{14}$N quadrupolar coupling constant ∣∣C$_{Q}$∣∣ ≈ 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$_{Q}$∣∣ > 3.5 MHz). This together with the information from $^{14}$N and $^{13}$C 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.