Polyiodides of amino acids. l-proline triiodides

Two new salts of l-proline containing triiodide anions were obtained and investigated: (l-ProH···l-Pro)(I₃) (I) and [(l-ProH)₃(l-Pro)](I₃)₃ (II). Both compounds crystallize in the polar monoclinic space group P2₁. Crystal structure determinations showed that (I) contains a dimeric cation formed by an O-H···O hydrogen bond with an O···O distance of 2.458(4) Å, while (II) features a peculiar tetrameric cation [l-ProH···(l-Pro-H-l-Pro)···l-ProH], where (l-Pro-H-l-Pro) is a pseudocentrosymmetric dimer with a very short hydrogen bond with an O···O distance of 2.427 Å. Infrared spectra of both crystals were registered and interpreted based on their structures. Electronic band structures were determined by quantum chemical calculations. The CASTEP code was used to calculate the band structures, total and partial density of states (TDOS, PDOS). Bandgaps were also measured by the diffuse reflectance method.