Vibrational Spectroscopy and Dynamics of Azide Ion in Ionic Liquid and Dimethyl Sulfoxide Water Mixtures

Abstract

Steady-state and time-resolved infrared spectroscopy of the azide (N(3)-) anion has been used to characterize aqueous mixtures both with the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF(4)]) and with dimethyl sulfoxide (DMSO). In the DMSO-water mixtures, two anion vibrational bands are observed for low water mole fractions (0 > X(w) > 0.25), which indicates a heterogeneous ion solvation environment. The band at 2000 cm(-1) observed for neat DMSO does not shift but decreases in amplitude as the amount of water is increased. Another band appears at slightly higher frequency at low X(w) (=0.05). As the amount of water is increased, this band shifts to higher frequency and becomes stronger and is attributed to azide with an increasing degree of hydration. At intermediate and high X(w), a single band is observed that shifts almost linearly with water mole fraction toward the bulk water value. The heterogeneity is evident from the infrared pump-probe studies in which the decay times depend on probe frequency at low mole fraction. For the azide spectra in IL-water mixtures, a single azide band is observed for each mole fraction mixture. The azide band shifts almost linearly with mole fraction, indicating nearly ideal mixing behavior. As with the DMSO-water mixtures, the time-resolved IR decay times are probe-frequency-dependent at low mole fraction, again indicating heterogeneous solvation. In both the DMSO and IL mixtures with water, the relaxation times are slower than would be expected from ideal mixing, suggesting that vibrational relaxation of azide is more sensitive than its vibrational frequency to the solvent structure. The results are discussed in terms of preferential solvation and the degree to which the azide shift and vibrational relaxation depend on the degree of water association in the mixtures.

Two-dimensional ultrafast vibrational spectroscopy of azides in ionic liquids reveals solute-specific solvation

“…The direct evidence of hydrogen bonding of N 3 with the imidazolium cation is subtle in the linear infrared spectrum. 28 Nevertheless, molecular modeling 42 the ionic liquid. There is a competition for this site near the imidizolium cation leading to the incorporation of the azide anion in the charged network.…”

“…1) or DMSO when compared to water, due to the special hydrogen bonding environment of water. [24][25][26][27][28] The linewidths of both kinds of azides in D 2 O and [BMIM][BF 4 ] are also similar.…”

Concentration‐Dependent Hydrogen‐Bonding Effects on the Dimethyl Sulfoxide Vibrational Structure in the Presence of Water, Methanol, and Ethanol

“…[6] Moreover, binary mixtures of DMSO with other co-solvents are of great interest in the fields of organic chemistry, chemical technology, and biology. [7] For instance, the DMSO/water system exhibits a strong nonideal mixing behavior [8] resulting in thermophysical properties-such as viscosity, density, surface tension, and freezing point-which significantly deviate from the expected values under the assumption of ideal mixing. To mention only one example, the freezing point decreases to as low as À70 8C compared to 18 and 0 8C for the pure liquids DMSO and water, respectively.…”

A novel intermolecular potential to describe the interaction between the azide anion and carbon nanotubes

“…Albeit the relatively large number of works on nitrogen chains, not so many other species were considered in a confined environment. In particular, despite the extensive literature investigating the spectroscopic features of the azide ion in crystal or gas phase [34][35][36][37][38][39][40][41][42] as well as solvated [43][44][45][46][47][48][49][50][51][52][53][54][55], N − 3 was never studied in a confined environment. Considering that N − 3 often represents a precursor in the synthesis of energetic molecules, e.g.…”