Assignment of N=N Vibrational Frequencies and Tautomeric Effects in the Vibrational Spectra of 1-Aryl-3-alkyl-3-hydroxy-triazenes and Their Platinum Complexes

Abstract

The vibrational frequencies of the N=N stretching mode of 1-aryl-3-alkyl-3-hydroxy-triazenes and their platinum complexes (PtL₄; L = triazene) were investigated by FT-IR and FT-Raman spectroscopy. The influence of electron-donating or -withdrawing substituents on the phenyl ring and of different alkyl substituents at the N³ atom on these frequencies was considered. The N=N vibrational frequency is significantly lowered (as a result of the delocalization of the N=N bond over three nitrogen atoms) compared to related compounds. The Pt complexes show a reduced intensity and an increased linewidth in the vibrational spectra. Additionally, the NMR spectra of the 1-aryl-3-alkyl-3-hydroxy-triazenes were recorded in order to show the tautomeric structure of these substances. The hydroxy triazenes preferentially exist in the N¹H form. As a consequence, the N=N stretching frequencies of the hydroxy triazenes appear to be influenced by the superposition of two counteracting effects, the delocalization of the N=N bond and tautomerism.