A Spinning Umbrella: Carbon Monoxide and Dinitrogen Bound MB<sub>12</sub><sup>–</sup> Clusters (M = Co, Rh, Ir) Ranajit Saha Susmita Kar Sudip Pan Gerardo Martínez-Guajardo Gabriel Merino Pratim K. Chattaraj 10.1021/acs.jpca.6b12232.s003 https://acs.figshare.com/articles/media/A_Spinning_Umbrella_Carbon_Monoxide_and_Dinitrogen_Bound_MB_sub_12_sub_sup_sup_Clusters_M_Co_Rh_Ir_/4865315 Strong binding of carbon monoxide (CO) and dinitrogen (N<sub>2</sub>) by MB<sub>12</sub><sup>–</sup> (M = Co, Rh, Ir) clusters results in a spinning umbrella-like structure. For OCMB<sub>12</sub><sup>–</sup> and NNMB<sub>12</sub><sup>–</sup> complexes, the bond dissociation energy values range within 50.3–67.7 kcal/mol and 25.9–35.7 kcal/mol, respectively, with the maximum value obtained in Ir followed by that in Co and Rh analogues. COMB<sub>12</sub><sup>–</sup> complex is significantly less stable than the corresponding C-side bonded isomer. The associated dissociation processes for OCMB<sub>12</sub><sup>–</sup> and NNMB<sub>12</sub><sup>–</sup> into CO or N<sub>2</sub> and MB<sub>12</sub><sup>–</sup> are highly endergonic in nature at 298 K, implying their high thermochemical stability with respect to dissociation. In OCMB<sub>12</sub><sup>–</sup> and NNMB<sub>12</sub><sup>–</sup> complexes, the C–O and N–N bonds are found to be elongated by 0.022–0.035 Å along with a large red-shift in the corresponding stretching frequencies, highlighting the occurrence of bond activation therein toward further reactivity due to complexation. The obtained red-shift is explained by the dominance of L←M π-back-donation (L = CO, OC, NN) over L→M σ-donation. The binding of L enhances the energy barrier for the rotation of the inner B<sub>3</sub> unit within the outer B<sub>9</sub> ring by 0.4–1.8 kcal/mol, which can be explained by a reduction in the distance of the longest bond between inner B<sub>3</sub> and outer B<sub>9</sub> rings upon complexation. A good correlation is found between the change in rotational barrier relative to that in MB<sub>12</sub><sup>–</sup> and the energy associated with the L→M σ-donation. Born–Oppenheimer molecular dynamics simulations further support that the M-L bonds in the studied systems are kinetically stable enough to retain the original forms during the internal rotation of inner B<sub>3</sub> unit. 2017-03-31 00:00:00 Rh M-L rotation OC N 2 B 9 ring σ- barrier complexation NNMB MB B 3 unit kcal OCMB NN bond dissociation energy values range Co red-shift binding B 9 rings CO complex donation Ir