Table 3.

NBO second-order perturbation stabilization energies for the dominant non-Lewis interactions, and the orbital interaction energies ΔE_orb for the dominant bonding interactions shown in Fig. 2a

	aNBO ΔE(2)					bETS-NOCV
	Stabilization interactions					ΔEorb
Compound	c1	c2	c3	d4	d5	σ2	π	σ1
${\left[{\mathrm{OU}}^{\mathrm{VI}}-\mathrm{O}\right]}^{2+}$ D∞h	2.2	14.2	1.8	29.8	29.8	−320.9	−168.6	−16.6
${\left[{\mathrm{OU}}^{\mathrm{VI}}-\mathrm{O}\right]}^{2+}$ C2v	0.8	7.9	1.6	21.0	21.0	−288.9	−164.7	−14.0
OUVI−C	2.1	11.7	2.4	79.7	42.9	−473.0	−317.2	−24.6
${\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NTh}}^{\mathrm{IV}}-\mathrm{Cl}$	0.0	0.0	0.0	11.6	28.2	−26.6	−10.7	0.0
${\left[{\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NTh}}^{\mathrm{IV}}-\mathrm{N}\right]}^{2-}$	1.0	7.1	1.1	82.4	13.8	−186.1	−101.8	−34.6
${\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NU}}^{\mathrm{VI}}-\mathrm{N}$	1.1	11.3	0.6	128.9	28.9	−287.1	−153.2	−28.3
${\left[{\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NU}}^{\mathrm{V}}-\mathrm{N}\right]}^{1-}$	0.4	8.0	0.4	112.1	19.6	−237.0	−120.2	−30.0
${\left[{\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NU}}^{\mathrm{IV}}-\mathrm{N}\right]}^{2-}$	0.8	7.3	0.7	73.5	24.5	−169.4	−83.4	−27.1
${\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NU}}^{\mathrm{V}}-\mathrm{O}$	0.0	6.0	0.0	79.8	22.6	−144.7	−70.2	−19.6
${\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NNp}}^{\mathrm{V}}-\mathrm{O}$	0.3	7.6	0.0	85.6	30.0	−172.7	−48.4	−17.4
${\mathrm{MeU}}^{\mathrm{VI}}{\left({\mathrm{R}}^{\mathrm{b}}\right)}_3-\mathrm{O}$	0.8	10.3	0.6	62.9	61.3	−179.3	−87.6	−19.6
${\mathrm{PhCCU}}^{\mathrm{VI}}{\left({\mathrm{R}}^{\mathrm{b}}\right)}_3-\mathrm{O}$	0.6	7.3	0.0	47.3	90.4	−166.8	−89.3	−16.7
CUVI−Oe	1.4	9.9	0.0	42.9	79.7	−209.1	−77.9	−13.7
$\mathrm{O}{\left({\mathrm{R}}^{\mathrm{b}}\right)}_3{\mathrm{U}}^{\mathrm{VI}}-{\mathrm{Me}}^e$	0.0	0.0	0.0	61.3	62.9	−82.6	−9.1	–
${\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NU}}^{\mathrm{VI}}-{\mathrm{N}}^{\mathrm{f}}$	1.2	10.3	0.6	81.0	21.2	−287.0	−152.6	−27.9

DFT/B3LYP calculations.

^a,bEnergies in kcal mol⁻¹.

^c,d Interactions illustrated in Fig. 2.

^a NBO second-order perturbation theory donor–acceptor ΔE⁽²⁾ stabilization energy.

^b ETS-NOCV contributions to ΔE_orb. The ΔE_orb and ΔE⁽²⁾ for the two π-bonding interactions are equivalent and only one is listed.

^cΔE⁽²⁾ donor–acceptor interactions involving 6s and 6p An semi-core shells.

^dΔE⁽²⁾ donor–interaction between the terminal and trans ligand lone pair and formally unoccupied An-centered NBOs. For the symmetric small compounds interactions nos. 4 and 5 are identical.

^eData for the trans–An bond for a selected compounds.

^fData for the full experimental ${\left({\mathrm{R}}^{\mathrm{a}}\right)}_3{\mathrm{NU}}^{\mathrm{VI}}\mathrm{N}$ structure for comparison.