Mass spectrometric and PM5 study of some piperidine-N-methyldiphosphonic acids and their complexes with alkali cations

Piperidine-N-methyldiphosphonic acid and its three methyl derivatives were synthesized. The complex formation of these acids with alkali cations was studied by the electrospray ionization mass spectrometry (ESI MS) and PM5 semiempirical method. The ESI spectra evidenced formation of protonated acids as well as complexes of both acids and their respective mono- and di-salts with monovalent cations. The main fragmentation pathway of the acids and their complexes was realized by elimination of H2O or H3PO3 molecules and depended on the cone voltage value. The structures of the acids and their complexes with monovalent cations were calculated by the PM5 method. The stabilization role of the intramolecular hydrogen bonds for the complexes is discussed.