NBO analysis of studied ion–CO₂ and DIL–CO₂ complexes calculated at M06-2x/cc-pVDZ level.

System	Donor NBO(i)	Acceptor NBO (j)	E(2)/kJ mol−1	ΔEij/a.u	F ij /a.u
Ion–CO 2 complexes
[Bis(mim)C5]2+–CO2	LP(1) O in CO2	BD*(1) C–HR	7.78	1.38	0.045
	LP(1) O in CO2	BD*(1) C–H1	3.51	1.38	0.03
[N111-C5-mim]2+–CO2	LP(1) O in CO2	BD*(1) C–HR	11.40	1.36	0.057
Imidazolium head	LP(1) O in CO2	BD*(1) C–HS	4.06	1.38	0.036
Ammonium head	LP(1) O in CO2	BD*(1) C–H13	5.61	1.37	0.038
	LP(1) O in CO2	BD*(1) C–H15	5.85	1.37	0.039
	LP(1) O in CO2	BD*(1) C–H18	5.77	1.37	0.039
[Bis(mim)C5-(C4)2]2+–CO2	LP(1) O in CO2	BD*(1) C–HR	9.66	1.37	0.05
	LP(1) O in CO2	BD*(1) C–H1	4.35	1.37	0.034
[NTf2]−–CO2	LP(1) N in [NTf2]−	BD*(3) C–O in CO2	11.51	0.58	0.036
	LP(2) O1′ in [NTf2]−	BD*(3) C–O in CO2	6.61	0.41	0.024
DIL–CO 2 complexes
[Bis(mim)C5][NTf2]2–CO2	LP(1) O in CO2	BD*(1) CR–HR	3.68	1.39	0.031
	LP(2) O in CO2	BD*(1) CR–HR	4.85	0.90	0.032
	LP(1) O1′ in [NTf2]−	BD*(3) C–O in CO2	5.61	0.99	0.035
	LP(3) O1′ in [NTf2]−	BD*(3) C–O in CO2	5.86	0.45	0.023
[N111-C5-mim][NTf2]2–CO2	LP(2) O in CO2	BD*(1) CR–HR	1.13	0.9	0.015
	LP(3) O in CO2	BD*(1) C1–H1	1.09	0.9	0.015
Imidazolium head	LP(1) O1′ in [NTf2]−	BD*(3) C–O in CO2	5.61	0.98	0.034
	LP(2) O1′ in [NTf2]−	BD*(3) C–O in CO2	4.64	0.44	0.021
Ammonium head	LP(1) O in CO2	BD*(1) CN1–H11	4.48	1.37	0.038
	LP(2) O in CO2	BD*(1) C4–H7	4.02	0.91	0.031
	LP(1) O1′ in [NTf2]−	BD*(3) C–O in CO2	4.69	0.98	0.032
	LP(3) O1′ in [NTf2]−	BD*(3) C–O in CO2	5.69	0.74	0.025
[Bis(mim)C5-(C4)2][NTf2]2–CO2	LP(1) O in CO2	BD*(1) CR–HR	3.81	1.39	0.032
	LP(2) O in CO2	BD*(1) CR–HR	5.35	0.9	0.033
	LP(1) O1 in [NTf2]−	BD*(2) C–O in CO2	3.68	0.98	0.028
	LP(1) O1 in [NTf2]−	BD*(3) C–O in CO2	3.30	1.00	0.027
	LP(1) O1 in [NTf2]−	BD*(3) C–O in CO2	4.93	0.98	0.030
	LP(2) O1′ in [NTf2]−	BD*(3) C–O in CO2	4.48	0.46	0.021