AB-INITIO STUDY OF THE INTERMOLECULAR INTERACTIONS IN THE HOFMANN CLATHRATES

The intermolecular interactions that take place in the Hofmann clathrates, Ni(NH3)(2)Ni(CN)(4) . 2(guest), have been studied by means of Hartree-Fock self-consistent field (HF) and second order Moeller-Plesset (MP2) calculations on the following model bimolecular systems: guest***CN- and guest***NH3 (guest = benzene, pyrrole, aniline, toluene), guest guest (guest = benzene, pyrrole), and benzene ethylenediamine. The interaction energies are calculated to be weakly attractive in most cases at the MP2 level and explain the relative stabilities of different clathrates and the orientation of the guest molecule relative to the host lattice. The effect of substituents of aromatic rings on the interaction energies was also analyzed by performing calculations on C(6)H(5)R***NH3 and C(6)H(5)R***C(6)H(5)R' systems (R, R' = NH2 CH3, H, F, CN, and NO2), and the relationship between the calculated binding energies (MP2) and the Hammett parameter of the substituents has been studied. From the analysis of the different interactions in which an aromatic ring participates, it is concluded that an aromatic molecule interacts laterally through its sigma system and frontally through its pi-system with ammonia or other aromatic rings.