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In resonance Raman (RR) spectroscopy, the laser excitation sources have often been found to be destructive towards polyiodides if compared with the milder conditions under which the Fourier transform Raman (FT-R) technique operates. In fact, our FT-R spectra of some model polyiodides—(CH 3 ) 4 NI 5 (I 5 − bent), (C 2 H 5 ) 4 NI 7 , and (CH 3 ) 4 NI 9 —are significantly different from the literature RR data, give evidence of decomposition of the samples in RR, and are in agreement, respectively, with the I − · 2I 2 , I 3 − · 2I 2 and (I − · 2I 2 ) · 2I 2 descriptions. In addition to the above-cited cases, the FT-R spectra of (Mn(modtc) 3 ]I s (modtc = morpholine carbodithioato) and (moH]I 5 (moH = morpholinium) 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 formulation. Moreover, the first FT-R spectrum of an I 16 4– anion in mo 2 ttl 2 I 16 , (mo 2 ttl 2+ = 3,5-di( N-morpholinio)-1,2,4-trithiolane), 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 correlation of the FT-Raman peaks with the molecular species, identified by the interatomic distances, is also observed in this case. Thus, a combination of X-ray structural data and FT-R data can provide a reasonable interpretation of the nature of the acceptor iodine moiety in charge-transfer polyiodide complexes.
Deplano et al. (Sat,) studied this question.