Mass spectrometric and theoretical study of polyiodides: the connection between solid state, solution, and gas phases

Area of Science:

• Inorganic Chemistry
• Physical Chemistry
• Mass Spectrometry

Background:

• Polyiodides are molecular species containing multiple iodine atoms bonded to a central iodide ion.
• Characterizing the structure and stability of polyiodides in the gas phase presents significant challenges.
• Previous studies have primarily focused on solid-state structures or lower-order polyiodide ions.

Purpose of the Study:

• To investigate the gas-phase stability and structure of polyiodide anions.
• To explore the formation of higher-order polyiodide ions beyond those previously reported.
• To demonstrate the utility of mass spectrometry for structural elucidation of novel inorganic species.

Main Methods:

• Electrospray ionization from acetonitrile solution to transfer polyiodides into the gas phase.
• Mass spectrometry (MS) analysis to detect and identify gas-phase polyiodide ions.
• Tandem mass spectrometry (MS/MS) for gas-phase fragmentation studies.
• Quantum chemical calculations to predict favored structures.

Main Results:

• Successful transfer and detection of intact polyiodide ions, including [I(11)](-), [I(13)](-), and [I(15)](-).
• Observation of ions with significantly higher iodine-to-iodide ratios than previously characterized.
• Theoretical calculations strongly favored branched structures for these polyiodides.
• Gas-phase fragmentation studies (MS/MS) corroborated the predicted branched structures.

Conclusions:

• Mass spectrometry is a powerful tool for characterizing gas-phase polyiodide structures.
• Branched structures are energetically favored for higher-order polyiodides in the gas phase.
• This work expands the known range of stable polyiodide species and their structural motifs.