Table 4 Selected axial pairwise steric exchange energies^a ΔE_X from NBO analysis for interactions between U 6p/6s and ligand valence NLMOs for the dominant interactions shown in Fig. 2a

\({[{{{{{{{\rm{O}}}}}}}}{-}{{{{{{{{\rm{U}}}}}}}}}^{{{{{{{{\rm{VI}}}}}}}}}{-}{{{{{{{\rm{O}}}}}}}}]}^{2+}\)

U 6p_σ ↔ O 2p_s

37.6

–

–

(1) :O ≡ U ≡ O:^b

U 6s ↔ O 2p_s

17.4

–

–

(2) O≣U ≡ O:

U 6p_σ ↔ O 2s_p

12.3

–

–

(3) :O ≡ U≣O

U 6s ↔ O 2s_p

0.9

–

–

U 6p_π ↔ O 2π^d

3.5

–

–

O−U^VI−C

U 6p_σ ↔ C 2p_s

9.6

8.0

9.1

(1) :C ≡ U ≡ O:^c

U 6s ↔ C 2p_s

5.6

4.8

5.6

(2) C≣U ≡ O:

U 6p_σ ↔ C 2s_p

10.2

12.8

12.7

(3) :C ≡U≣O

U 6s ↔ C 2s_p

3.3

4.0

2.9

U 6p_π ↔ C 2π^d

0.3

0.3

0.3

U 6p_σ ↔ O 2p_s

36.2

36.4

40.0

U 6s ↔ O 2p_s

12.2

12.3

12.9

U 6p_σ ↔ O 2s_p

9.7

9.3

1.5

U 6s ↔ O 2s_p

0.2

0.1

0.5

U 6p_π ↔ C 2π^d

3.6

3.6

3.6

\({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{{\rm{N}}}}}}}}}_{{{{{{{{\rm{amine}}}}}}}}}{-}{{{{{{{{\rm{U}}}}}}}}}^{{{{{{{{\rm{VI}}}}}}}}}{-}{{{{{{{{\rm{N}}}}}}}}}_{{{{{{{{\rm{nitride}}}}}}}}}\)

U 6p_σ ↔ N_nitride 2p_s

34.0

32.3

23.5

(1) \({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{\rm{N}}}}}}}}\): U ≡ N:^c

U 6s ↔ N_nitride 2p_s

11.5

12.8

8.5

(2) \({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{\rm{N}}}}}}}}{-}{{{{{{{\rm{U}}}}}}}}{\equiv} {{{{{{{\rm{N}}}}}}}}\):

U 6p_σ ↔ N_nitride 2s_p

9.1

10.0

18.5

(3) \({({{{{{{{{\rm{R}}}}}}}}}^{{{{{{{{\rm{a}}}}}}}}})}_{3}{{{{{{{\rm{N}}}}}}}}\): U≣N

U 6s ↔ N_nitride 2p_s

1.3

0.4

4.3

U 6p_π ↔ N_nitride 2π^d

2.3

2.3

2.3

U 6p_σ ↔ N_amine 2s_p

8.4

8.6

8.8

U 6s ↔ N_amine 2s_p

4.2

3.3

4.1