PhD defence Musleh U. Munshi on Infrared spectroscopic characterization of functional molecular ions in the gas phase

3D structures of molecular ions are crucial to determine their functions.  Most often this involves the change of the charge states via oxidation-reduction (redox) reactions. Understanding the subtle underlying mechanisms are necessary in order to improve the quality, for instance, to design a better medicine to combat disease while minimizing any side effect.

During his PhD, Musleh investigated the effect of charge on the molecular structure of isolated ions including the interaction of transition-metal ion with neutral ligands (metal ion bound small molecules) in various coordination patterns especially tetra and hexa-coordinated metal ions. He focused on how the number of d-electrons of the metal ion affects the geometry of the complexes as the charge state changes, for instance from 2+ to 1+ ion.

Isolating the molecular system in the gas-phase has the advantage that it removes the crowded environment, which brings greater simplicity not only to the experiment but also to the theoretical modelling. For instance, density functional theory (DFT) based modelling has been used to predict spectroscopic and electronic structure properties, and usually return accurate results thanks to the absence of any solvent environment. In general, despite the enormous successes of DFT, it is often challenging to predict the physical and spectroscopic properties for open-shell (having an unpaired electron) systems. Moreover, open-shell electronic systems with transition metals are notoriously difficult to model because of the presence of near-degeneracy correlation among the partially filled d shells. Experimental data of these systems can aid in the development of theoretical methods, especially when the data are taken in pure isolation, mitigating complications arising from including the effects of an environment in the calculations. Gas-phase experimental data of open-shell systems are therefore not only extremely valuable for the theoretical development, but also help understand the existing limitations of theoretical methods. The theory would thus serve to predict the best systems for molecular functionality on the one hand, and it would help to better understand the experiment on the other hand. In this regard, mass spectrometry coupled with tunable infrared laser(s) offers an opportunity to scrutinize the intrinsic spectroscopic and structural properties of ionic complexes in the gas phase.  In his thesis, he showed that the charge state has a direct effect on the geometry of the complexes. This conclusion has been possible because of the direct match between the experimental infrared spectra of the mass-to-charge (m/z) isolated molecular systems and the predicted linear infrared spectra.

Some textbooks should be rewritten

Infrared ion spectroscopy is not only useful for determining the functional groups but also the global 3D structures of the isolated molecular species. The most interesting moment of the PhD was watching the experiment, employing infrared free-electron laser while probing the resonance vibrational frequencies of the molecules, confirm the predictions.

Defence

Musleh U. Munshi defended his doctoral thesis on 15 October 2019.
Supervisor: prof. Jos Oomens
Co-supervisor: dr. Giel Berden