Interaction in molecular crystals, 166. Polyiodo molecules I2C=CI2, (IC)(4)S, (IC)(4)NH, (IC)(4)N-CH3 and HCI3: Structure determination following crystallization or by density functional theory calculation

The structures of tri- and tetraiodo-substituted carbon compounds are deter mined either experimentally by X-Ray Structure Analysis or, because crystal lization of tetraiodothiophene could not be achieved, approximated by Densi ty Functional Theory optimization of structural data from a donor/acceptor complex. The structures show noteworthy details such as a second polymorph of tetraiodoethene crystallized by sublimation or herringbone crystal packi ng patterns of tetraiodopyrrole derivatives. All molecular geometries are d iscussed and compared based on relativistic density functional theory calcu lations with 6-31G* basis sets including iodine pseudopotentials. They repr oduce even finer structural details due to van der Waals repulsion of the b ulky iodo substituents. Natural Bond Orbital (NBO) charge distributions sug gest positive partial charges at all iodine centers with the strongest pola rization Cdelta--->Idelta+ in HCl3, which contains well over 97% iodine.