Vibrational spectra and structure of complexes containing the hydrogen dinitrate ion

Infrared and Raman spectra of solid hydrogen dinitrate complexes with K⁺, Rb⁺, Cs⁺, (CH₃)₄N⁺, trans-(Co py₄Cl₂)⁺, Ph₄As⁺, Ph₄P⁺, (C₂H₅)₄N⁺ and (C₄H₉)N⁺ have been recorded and analyzed. The assignments were assisted by deuteration and, in the case of the Cs⁺, (CH₃)₄N⁺, and Ph₄As⁺ complexes, by ¹⁵N substitution. Infrared spectra at 50 kbar of the (CH₃)₄N⁺ complex were also recorded. The salient features of the i.r. spectra are the lack of fundamental OH bands above 1800 cm⁻¹ and the appearance of a strong absorption centered at about 600 cm⁻¹, both indicating very strong hydrogen bonding. The i.r. and Raman spectra permit the differentiation between the planar and nonplanar types of the hydrogen dinitrate ion.