HOST-GUEST INTERACTIONS IN THE PYRROLE AND ANILINE HOFMANN CLATHRATES - A THEORETICAL-STUDY

Extended Huckel tight binding (EHTB) band calculations are reported for the Hofmann clathrates Ni(NH3)(2)Ni-(CN)4 . 2G (G = pyrrole or aniline) and Ni(en)Ni(CN)(4) . 2C(6)H(6) (en = ethylenediamine). The crystal orbital displacement (GOD) and integrated crystal orbital displacement (ICOD) functions were used to detect the nature of the interacting orbitals and to study the role of the different building blocks of the host lattice in the host ... guest interaction. The main orbital interactions identified correspond to electron density donation from the pi system of the guest molecules to empty orbitals of the host lattice, mostly sigma*(N-H), and from the pi(C-N) orbitals of the host to the sigma*(C-H) orbitals of the guest, with no significant participation of the transition metal atoms. Changes in bond distances of the host and guest sublattices and variations of vibrational frequencies, such as CN and N-H stretches of the host lattice produced by enclathration are correlated with variations in the calculated overlap populations, accounting for the axial elongation of the pyrrole guest molecule, in contrast to the compression predicted for benzene.