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