X-Ray and NMR Studies of a Diammonium (Nitrilo-triacetato)dioxovanadate(V) Complex

A new vanadium(V) complex, diammonium (nitrilo-triacetato)dioxovanadate(V) (NH₄)₂ [VO₂NTA], has been synthesized. The structure of the complex has been studied by solution and solid-state NMR spectroscopies as well as single crystal X-ray crystallography. It is confirmed from NMR studies that the octahedral geometry is retained in both solution and solid-state of the complex. The chemical exchange between glycinate rings cis to and trans to V=O bond in the complex has been observed in the solution ¹³C NMR spectra at elevated temperatures. Large ⁵¹V chemical shift anisotropy (Deltadelta_aniso = -800 ppm) and quadrupole coupling (e²qQ/h = 8.80 MHz) were observed in ⁵¹V spectra of the solid complex, as shown in Fig. 1. Distortion of octahedron also results in an increase of the electric field gradient at a V nucleus. The NMR spectra are discussed on the basis of the crystal structure.

Fig. 1. ⁵¹V NMR spectra of the powder (NH₄)₂[VO₂NTA]. (a) MAS and (b) off-MAS spectra measured at (A) 105.25 MHz and (c) off-MAS spectra at 52.64 MHz. The spinning rates were (a,b) 10.00 kHz and (c) 12.00 kHz.