The structures of a series of decaphenyl metallocenes (Ph 5 Cp) 2 M, which model superbulky metallocenes, are calculated by means of density functional theory including a semi-empirical correction for dispersion interactions (DFT+D). Through a detailed investigation of the calcocene it is shown that the interactions between the phenyl substituents of the two cyclopentadienyl ligands lead to a preference of S 10 symmetrical structures and that dispersion interactions contribute to the overall stability of superbulky metallocenes. Whereas
The interactions in the complexes of tetracyanothylene (TCNE) with benzene and p-xylene, often classified as weak electron donor-acceptor (EDA) complexes, are investigated by a range of quantum chemical methods including intermolecular perturbation theory at the DFT-SAPT (symmetry-adapted perturbation theory combined with density functional theory) level and explicitly correlated coupled-cluster theory at the CCSD(T)-F12 level. The DFT-SAPT interaction energies for TCNE-benzene and TCNE-p-xylene are estimated to be -35.7 and -44.9 kJ mol(-1), respectively, at the complete basis set limit. The best estimates for the CCSD(T) interaction energy are -37.5 and -46.0 kJ mol(-1), respectively. It is shown that the second-order dispersion term provides the most important attractive contribution to the interaction energy, followed by the first-order electrostatic term. The sum of second- and higher-order induction and exchange-induction energies is found to provide nearly 40 % of the total interaction energy. After addition of vibrational, rigid-rotor, and translational contributions, the computed internal energy changes on complex formation approach results from gas-phase spectrophotometry at elevated temperatures within experimental uncertainties, while the corresponding entropy changes differ substantially.
Protonated methane, CH, is not only subject to quasi-rigid vibrational motion which describes its unprotonated parent, CH, but is dominated by large-amplitude motion even in its quantum ground state. This fluxional behavior leads to hydrogen scrambling which sensitively depends on the underlying flat potential energy surface. Yet, it is largely unknown how fluxional species, such as CH, respond to perturbations arising from microsolvation by weakly interacting species, such as those commonly used as tags in messenger-based vibrational action spectroscopies. Here, we construct an intermolecular interaction potential of extrapolated coupled cluster accuracy in order to investigate the microsolvation shell structure of small CH·He complexes. Having explicitly demonstrated that three-body contributions are essentially negligible, our analytical CHHe model potential is kept as simple as possible in order to allow for efficient use in the framework of finite-temperature path integral simulations. It is a strictly pairwise additive site-site potential without explicit angular dependence, but critically involves additional pseudo-sites in addition to the usual atom-based interaction sites. The parameterized potential is shown to accurately describe the microsolvation of all low-lying stationary points on the potential energy surface, namely the e-C, s-C, C, and C structures. Based on path integral Monte Carlo simulations at ultralow temperature, about 1 K, we disclose that the many-body helium density in three-dimensional space, and thus the microsolvation pattern, depends sensitively on the combination of the solute structure and the number of attached He atoms.
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