FT-RAMAN STUDY ON CHARGE-TRANSFER POLYIODIDE COMPLEXES AND COMPARISONWITH RESONANCE RAMAN RESULTS

In resonance Raman (RR) spectroscopy, the laser excitation sources hav e often been found to be destructive towards polyiodides if compared w ith the milder conditions under which the Fourier transform Raman (FT- R) technique operates. In fact, our FT-R spectra of some model polyiod ides-[(CH3)(4)N]I-5 (I-5(-) bent), [(C2H5)(4)N]I-7, and [(CH3)(4)N]I-9 -are significantly different from the literature RR data, give evidenc e of decomposition of the samples in RR, and are in agreement, respect ively, with the I-.2I(2), I-3(-).2I(2) and (I-.2I(2)).2I(2) descriptio ns. In addition to the above-cited cases, the FT-R spectra of [Mn(modt c)(3)]I-5 (modtc = morpholine carbodithioato) and [moH]I-5 (moH = morp holinium) are reported. The crystal structures indicate that in these two compounds the I-5(-) anions can be properly described as I-.2I(2) and I-3(-).I-2, respectively, and FT-R spectra agree well with this fo rmulation. Moreover, the first FT-R spectrum of an I-16(4-) anion in ( [mo(2)ttl]I-2(16), ([mo(2)ttl](2+) = 3,5-di(N-morpholinio)-1,2,4-trith iolane), whose X-ray structure shows a sequence of two I-3(-)... I-2.. . I-.I-2 (I-8(2-)) interacting anions, is reported. A close correlatio n of the PT-Raman peaks with the molecular species, identified by the interatomic distances, is also observed in this case. Thus, a combinat ion of X-ray structural data and FT-R data can provide a reasonable in terpretation of the nature of the acceptor iodine moiety in charge-tra nsfer polyiodide complexes.