Elucidation of chemical fragmentation mechanisms of cubic magnesium alkoxide compounds using electrospray ionization method

In this study, single-source organometallic magnesium precursor compounds, [MeMgOR']4 (R'=iPr, tBu, CyHex) and Me6Mg7(OR)8 (R= Et, nPr, nBu), were synthesised and subsequently characterised by mass spectrometry. The importance of these precursors is emphasised by their ability to facilitate the synthesis of MgO nanoparticles without requiring high temperatures, high vacuum conditions, complex procedures or significant costs, as usually required by contemporary methods. These features offer researchers significant advantages in terms of time, energy and cost efficiency. It is known that the organic groups separated from the metal alkoxide structure during the synthesis of these nanoparticles form structure defects that cause MgO nanoparticles to have wide application areas. However, there is no detailed study on the degradation mechanism of these metal alkoxide model compounds and the resulting degradation products. Determination of the degradation products and the separated ligand groups that occur during the degradation process of metal alkoxide compounds may help to know the ligand effect on the defect structure of the compounds and thus to synthesise MgO nanoparticles with controllable defect structure in future studies. This study represents the first detailed analysis of the synthesised precursor compounds using mass spectrometry. Mass spectra of both the molecular compounds and the resulting degradation products were obtained and extensive discussions on the potential degradation mechanisms of the precursor compounds were carried out. The synthesised precursor compounds show high sensitivity to air and water and degrade rapidly upon exposure. Therefore, Electrospray Ionisation (ESI), which is considered as one of the most gentle ionisation techniques, was used in mass spectrometric analyses. Findings from mass spectrometric studies indicate that metal alkoxide precursor compounds are predominantly degraded via gamma hydrogen elimination, resulting in the removal of alkene groups from the structure. The detectable end products of these decompositions are the compounds (MgO)-H and Mg(OH)₂, which represent the penultimate step in the synthesis of MgO. MS/MS experiments were also carried out to obtain more detailed data on the compounds and the data obtained were found to be in agreement with the data obtained from the main spectrum.