A Spinning Umbrella: Carbon Monoxide and Dinitrogen Bound MB12- Clusters (M = Co, Rh, Ir)

作者：Saha Ranajit; Kar Susmita; Pan Sudip^*; Martinez Guajardo Gerardo; Merino Gabriel^*; Chattaraj Pratim K^*

来源：Journal of Physical Chemistry A, 2017, 121(15): 2971-2979.

DOI：10.1021/acs.jpca.6b12232

Strong binding of carbon monoxide (CO) and dinitrogen (N-2)by MB12- (M = Co, Rh, Ir) clusters results in a spinning umbrella-like structure. For OCMB12- and NNMB12- 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. COMB12- complex is significantly less stable than the corresponding C-side bonded isomer. The associated dissociation processes for OCMB12- and NNMB12- into CO or N-2 and MB12- are highly endergonic in nature at 298 K, implying their high thermochemical stability with respect to dissociation. In OCMB12- and NNMB12- complexes, the C-O and N-N bonds are found:to be elongated by 0.022-0,035 A 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 pi-back-donation (L = CO, OC, NN) over L -> M sigma-donation. The binding of L enhances the energy barrier for the rotation of the inner B-3 unit within the outer B-9 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-3 and outer B-9 rings upon complexation, A good correlation is found between the Change in rotational barrier relative to that in MB12- and the energy associated with the L -> M sigma-donation. Born-Oppenheimer molecular dynamics simulations further support that the M-L bond in the studied systems are kinetically stable enough to retain the original forms during the internal rotation of inner B-3 unit.

• 出版日期2017-4