Metal-dependant structural families of aminomethylphosphonic acid assemblies differentiated by ion mobility mass spectrometry and density functional theory

Herein the morphology of aminomethylphosphonic acid (AMPA)–metal aggregates are analysed by ion mobility-mass spectrometry, DFT and IRMPD spectroscopy. Matching experimental collision cross section to the DFT predicted minima allowed unambiguous assignment of [M(AMPA)(AMPA-H)]+ where M = Mg$^{2+}$, Ca$^{2+}$, and Mn$^{2+}$. Two distinct structural families of [M(AMPA)(AMPA-H)]$^+$ where M = Mg$^{2+}$, Ca$^{2+}$, Sr$^{2+}$, Ba$^{2+}$, Mn$^{2+}$, Cu$^{2+}$, and Zn$^{2+}$ were differentiated by ion mobility mass spectrometry. Groupings of experimental collision cross sections were observed for a square pyramidal geometry, (M = Ca$^{2+}$, Sr$^{2+}$, Ba$^{2+}$) versus a seesaw geometry (M = Mg$^{2+}$, Mn$^{2+}$, Cu$^{2+}$, and Zn$^{2+}$), paving the way for distinction of aggregates at the earliest stages of assembly.