Nature of the valence excited states of bromine in the T and P clathrate cages

Abstract

The guest-host intermolecular potentials for the valence excited states of Br in the tetrakaidecahedral(T) and pentakaidecahedral(P) clathrate cages have been calculated using ab initio local correlation methods. We find that the excited states are more strongly bound than the corresponding ground states even in the small T cage where bromine has a tight fit. The angular dependence of the interaction energies is quite anisotropic; this reflects in the corresponding electronic shifts where regions of maxima for blue-shifts in the T cage indicate the presence of halogen bonding. We predict a large temperature dependence of the electronic shifts and compare absolute values with recent experimental studies. This stringent test indicates the reliability of local correlation treatments to describe weak intermolecular forces in ground and excited states.

Halogen Bonds in Clathrate Cages: A Real Space Perspective

“…In particular the role of the ionic component as indicator of halogen bonding was stressed. This was further confirmed by performing a more thorough calculation of the electronic shifts taking into account the rotational motion of the dihalogen inside the cages . Another important set of experiments probed the structural characteristics of chlorine and bromine clathrates in X‐ray measurements .…”

“…This was further confirmed by performing a more thorough calculation of the electronic shifts taking into account the rotational motion of the dihalogen inside the cages. [14] Another important set of experiments probed the structural characteristics of chlorine and bromine clathrates in Xray measurements. [5] The case of chlorine has a long and interesting history starting with its accidental discovery by sir Humphrey Davy [15] in 1811, followed by the first X-ray determination in 1952 by Pauling and Marsh [16] where using van der Waals radii arguments it was assumed that chlorine would not fit in the smaller dodecahedral cage and the recent detailed study by the group of Ripmeester showing that more than 30 % of the 5 12 dodecahedral cages are occupied [5] .…”

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

“…The geometry of the water in each cage was fixed according to their experimental values 6,7,30,31 in the TS-I and CS-II structures as has been done in all of our previous studies. 9,12,13 The oxygen positions were obtained in X-ray experiments and the hydrogen atoms are arranged as to yield cages with low values of the dipole moment. 32 The halogen molecule was positioned in the center of the cage and its intramolecular distance was fixed to the optimal value in the isolated diatomic as provided by the DF-LMP2/AVTZ level of theory (2.29 Å).…”

“…Although the local methods make an important reduction 12,13,28 of the basis set superposition error (BSSE), the presence of several water molecules led to a non-negligible BSSE, and for this reason, we have applied the usual counterpoise procedure. 35,36 We report total inclusion energies at the DF-LCC2 level of theory.…”

“…We used a combination of analysis of the components of the interaction energy in the ground state but also looked at the interaction in the valence excited states which is expected to be repulsive in the case of XB in the excited states since the electronic transition involved places an electron in the region of the sigma hole characteristic of XB. [10][11][12][13] The nature of the halogen bond and its relevance in a variety of supramolecular structures has been the subject of intense research in the recent past. [14][15][16][17][18][19] It is interesting to point out two pioneer studies in the field of van der Waals complexes which were precursors to the definition of halogen bonding.…”