Dinitrogen Splitting without Barrier or Visible Light-Driven: Reactions of Vanadium Trimers and Dimers with Dinitrogen

Abstract

The reaction of V atoms and small clusters with dinitrogen has been investigated by matrix isolation in solid Ne and by complementary quantum chemical calculations. The experiments disclose striking differences between the reactivity of V atoms, dimers, and trimers toward dinitrogen. Whereas V atoms react only by formation of complexes, both V₂ and V₃ react by cleavage of the N₂ triple bond to form nitride clusters. Whereas V₃ reacts immediately at the conditions of matrix deposition, the reaction of V₂ requires activation by irradiation with visible light. There is evidence for two isomers of V₂N₂, a planar one with a ⁵A_u electronic term and a long V─V distance, and a folded one with a ¹A₁ term and a short V─V distance. Furthermore, there are also complexes of V₂ and V₃ with N₂ that contain activated N₂ units.

Keywords: cluster; density functional calculations; matrix isolation; nitrogen activation; vanadium.

Figure 1

Infrared spectra of Ne matrices (4 K) containing V and N₂ in the range 600 − 900 cm⁻¹, after deposition, after annealing to 10 K, after visible light irradiation for 10 min, after anew annealing to 10 K, after UV light irradiation for 10 min, and after a further annealing to 10 K.

Figure 2

Infrared spectra of Ne matrices containing V and N₂ recorded directly after deposition in the range 1900 − 2200 cm⁻¹, using ¹⁴N₂, using ¹⁵N₂, using a mixture of ¹⁴N₂ and ¹⁵N₂, and using a mixture of ¹⁴N₂, ¹⁴N¹⁵N, and ¹⁵N₂.

Figure 3

Infrared spectra of Ne matrices containing V and N₂ after irradiation with visible light for 10 min and subsequent annealing to 10 K in the range 600 − 900 cm⁻¹, using ¹⁴N₂, using ¹⁵N₂, using a mixture of ¹⁴N₂ and ¹⁵N₂, and using a mixture of ¹⁴N₂, ¹⁴N¹⁵N, and ¹⁵N₂.

Figure 4

Infrared spectra of Ne matrices containing V and N₂ after irradiation with visible light for 10 min and subsequent annealing to 10 K in the range 500–600 cm⁻¹, using ¹⁴N₂, using ¹⁵N₂, using a mixture of ¹⁴N₂ and ¹⁵N₂, and using a mixture of ¹⁴N₂, ¹⁴N¹⁵N, and ¹⁵N₂.

Figure 5

Structures of different isomers of VN₂ from TPSS/def2‐TZVP calculations.

Figure 6

Structures of different isomers of V₂N₂ from TPSS/def2‐TZVP calculations.

Figure 7

Structures of different isomers of V₃N₂ from TPSS/def2‐TZVP calculations.

Figure 8

Relative energies of different excited electronic terms of V₂N₂ by Davidson‐corrected MRCI calculations at the structures of the ⁵A_u and ¹A₁ terms.