This study analyzed the initial adsorption and activation of CO2 on bimetallic CunSc nanoclusters, with n = 3–7, using DFT calculations in ORCA with the r2SCAN-3c method. A total of 20 bare clusters and their corresponding CunSc–CO2 complexes were investigated, considering four structural configurations for each composition. To avoid classification based solely on adsorption energy, a global CO2 activation index was developed and defined as IACO2 = z(AG) + z(CTCO2) + z(Bending) + z(ΔrC–O). In this index, AG = −ΔGads, CTCO2 = −qCO2, bending corresponds to (180° − ∠O–C–O), and (ΔrC–O) represents the average elongation of the C–O bonds. This descriptor enabled distinguishing complexes that only stabilize CO2 from those that induce effective geometric and electronic activation. Although 5IV and 3IV exhibited favorable adsorption, with (ΔGads) values of −52.978 and −53.494 kcal mol−1, respectively, their molecular activation was low, with nearly linear CO2 and minimal or unfavorable charge transfer. In contrast, 7III and 7II showed the highest activation, with CTCO2 values of 1.206 and 1.163, bending values of 69.867° and 68.869°, and C–O elongations of 0.208 and 0.195 Å, respectively. The standardized (IACO2) ranking identified 7III, 7II, 3III, and 3II as the most relevant systems, with scores of 100.0, 93.8, 88.2, and 86.8, respectively. These results show that CO2 activation on CunSc nanoclusters should not be assessed solely by (ΔGads), but rather by a multi-criteria approach that accounts for stability, charge transfer, and molecular distortion.
Paternina et al. (Wed,) studied this question.