Nature of the guest-host interactions for dibromine in the T, P, and H clathrate cages

Abstract

The guest-host intermolecular potentials for the ground states of Br in the tetrakaidecahedral (T), pentakaidecahedral (P), and hexakaidecahedral clathrate (H) cages have been calculated using ab initio local correlation methods. Applying the local correlation energy partitioning analysis together with first-order symmetry adapted perturbation theory, we obtain a detailed understanding of the nature of the interactions. In particular, the debated question concerning the possible presence of halogen bonding (XB) is carefully analyzed. In the case of the T cage, given its smaller size, the Br-O distance is too short leading to a larger exchange-repulsion for XB orientations which therefore do not represent minima. For the other two cages, the Br-O distance is too large leading to little orbital overlap effects and thus weaker donor-acceptor interactions; however, these orientations coincide with the global minima.

Halogen Bonding and Cooperative Effects in Chlorine Clathrate: Ab Initio Periodic Study

“…The results shown here complement those obtained in isolated cages, , and even though the inclusion energies are less attractive in the periodic model, the main trends are the same: the PES are similar, more attractive inclusion energies are observed in the 5 12 6 2 cage, there is evidence of halogen bonding in the 5 12 cage, and the general nature of the Cl–O interaction is the same. It is worth mentioning that, in the case of Br 2 , calculations on isolated cages suggest that there are no XB interactions.…”

“…In the past, there has been a mention of a possible multidirectional halogen bonding; 1 we present here a different interpretation where the global minimum shows features associated with XB interactions, but there are regions within 1 kcal/mol that do not exhibit the characteristic features of halogen bonding. The results shown here complement those obtained in isolated cages, 16,36 and even though the inclusion energies are less attractive in the periodic model, the main trends are the same: the PES are similar, more attractive inclusion energies are observed in the 5 12 6 2 cage, there is evidence of halogen bonding in the 5 12 cage, and the general nature of the Cl−O interaction is the same. It is worth mentioning that, in the case of Br 2 , calculations on isolated cages suggest that there are no XB interactions.…”

“…The relevance of other components of the interaction energy such as exchange repulsion, induction, and charge transfer has been documented on previous studies for isolated cages. 16,36 In particular, exchange repulsion can be a determining factor for the most stable orientations. Although dispersion is the main attractive component, it is more isotropic and does not play a significant role in determining the most stable geometries.…”

Halogen Bonds in Clathrate Cages: A Real Space Perspective

“…[2] The nature of guest-host interactions in the case of dihalogen molecules in water clathrate cages 1 has been the subject of recent debate in both experimental [3][4][5] and theoretical studies. [6][7][8][9] The initial interpretation of the observed electronic shifts in ultraviolet and visible spectra of bromine clathrate assumed that halogen bonding could not be responsible since all the water lone-pairs are involved in hydrogen bonding of the water lattice and thus not available for halogen bonding. [3] In contrast the much larger blue-shifts observed in bromine aqueous solutions were consistent with the formation of halogen bonding interactions.…”

Density Functional Study on the Fundamental and Valence Excited States of Dibromine in T, P, and H Clathrate Cages

“…Halogen molecules like Br 2 or Cl 2 are excellent probes of their surrounding environment. The beautiful spectroscopic experiments by Janda and Apkarian’s groups showed that the maximum absorption peak in UV–vis absorption experiments shifts in different amounts in aqueous systems. − The observed blue-shift is due to the intermolecular interactions present, from the “classical” halogen bond (XB) to some variants. − The latest diffraction experiments by Udachin et al confirmed that Cl 2 is hosted in a cage almost too small to fit in, and so it also is for Br 2 . , This result evidenced that the guest–host interactions should go beyond the weak van der Waals regime since the free diameter of the 5 12 cages is estimated at ∼5.0 Å, and the van der Waals size of dichlorine is 5.5 Å. Recently, our group showed that the stabilization of Cl 2 @5 12 , Cl 2 @5 12 6 2 , and Br 2 @5 12 6 2 is the result of a subtle balance of forces.…”