IR absorption spectroscopy of polarized states of the [D2O...D-OD2]+ ion in crystalline deuterodioxonium perchlorate

Polymorphism of crystalline DClO₄·2D₂O with 99 at % D has been studied by IR absorption spectroscopy. A new phase has been found, which is easy to identify based on some spectral indications: the spectra show a strong broad band at 2125 cm^?1 due to v_s,as(D₃O) vibrations of the deuterodioxonium group and a rather narrow strong band at 2506 cm^?1 due to the v_as(D₂O) vibrations of the neutral molecular group. The continuous band v_as(O...D...O) typical of the intracationic hydrogen bond in D₅O ₂ ⁺ ClO ₄ ^? is absent in this case. These features point to considerable polarization of the deuterooxonium cation D₂O...D-OD₂]⁺. Its low symmetry is explained by a considerable displacement of the bridging D atom from the center of the strong hydrogen bond to one of the two D₂O molecules induced by asymmetric interactions in the crystal field. The ClO ₄ ^? ions bound by the hydrogen bonds of dioxonium are also in low-symmetry positions. Upon the crystallization of DClO₄·2D₂O with ≥10 at % H, a polymorphic isotope effect is observed: the crystal structure depends on H-D isotope dilution, the conditions of thermal treatment of all samples being the same.