Theoretical and experimental (infrared and Raman) study of the host-guest interactions in some Hofmann type clathrates

The host-guest interactions in some clathrate-type compounds were studied e xperimentally and theoretically. Room temperature (RT) and low temperature (LT similar to 100 K) IR, and RT Raman spectra of Hofmann clathrates of the type M(NH3)(2)M' (CN)(4). 2C(6)H(6) (where M epsilon {Ni, Co, Cd, Fe, Mn, Mg, Zn} and M' epsilon {Ni, Pd, Pt}) were recorded. The spectral data show that the positions of almost all bands due to the guest molecule (except th ose from the gamma(CH) modes) remain practically unchanged on enclathration . The frequencies of the gamma(CH) modes increase with the decrease of the host unit cell volume in a series of structurally similar clathrates, and w ith the decrease of temperature, the first effect being more pronounced. A quantum theoretical model is proposed to get some insight into the relative importance of particular effects on the spectral behavior of the guest mol ecule upon enclathration, in which both local electrostatic field and anhar monicity effects are included. The predictions of the model are in qualitat ive agreement with the experimental observations. (C) 1999 Elsevier Science B.V. All rights reserved.