Nb and Ta from Group V are borderline at ∼ 26 kcal/mol, whereas V and all the Group IV metals are surmountable at ≤ 23 kcal/mol. A strong linear correlation is found between the activation energy and both the length of the O -O peroxycarbonate bond in the preceding intermediate, int2, (R 2 = 0.94, Figure ) and the same partially cleaved O -O bond in the transition state, ts2 (R 2 = 0.95, Figure ). Most of the energy cost of distorting int2 to form ts2 can, thereby, can be ascribed to elongation of the aforementioned O -O bond. Since the Group VI metal compounds have the most contracted peroxycarbonate O -O bonds-1.425 Å to 1.429 Å compared to 1.456 Å for free CO 4 2 --more energy is required to distort them to their respective transition state values than is the case for the Group IV metals (Table ). When evaluating this finding from the lens of electronic structure, the importance of a particular KS orbital becomes evident. ), and an energy of -6.3 eV. When incorporated into the complex, this orbital, through various interactions with the [M(O 2 ) 3 ] -fragment, including from a symmetry allowed d-orbital on the metal center, lowers in energy to some value between -6.5 eV for Ti and -8.7 eV for Mo (Table ). This KS orbital corresponds to either a HOMO-3 or HOMO-5 in int2. As shown in Figure bond in int2 is the longest and easiest to cleave for M --Ti relative to the other eight complexes. Although it is outside the scope of this study, metals beyond the Group IV/V/VI block studied could also have useful chemical properties relevant to DAC. If the trends identified here are extrapolated, the Group VII and higher complexes should have prohibitively high activation barriers for CO 2 capture and experience strong competition from auto-degradation. Conversely, Group III metal centers hold more appeal given their likely similar chemical behavior to Group IV. (Note that none of the metals in Group III or Group VII and higher have, to our knowledge, been synthesized