Hydrogen bond acidic methylphosphonate

The partially protonated cyclen and cyclam and their derivatives are present in aqueous solution in some stable conformations stabilized by intramolecular hydrogen bonds. It leads, for example, to broad signals in NMR at room temperature and intermediate pH. Such hydrogen bond-stabilized structures are sometimes rather stable as it was proved, for example, in the case of l,8-bis(methylphosphonic acid) cyclam derivatives where solution structure is probably the same as found in the solid state <2000CCC1289>. These closed structures are opened after full protonation. 

In addition, the Traer group also studied the proton-conducting dynamics of imidazole methylphosphonate. The P CODEX NMR showed that the rotation of the methylphosphonate has a low activation energy implying that the motion of the anion is not impeded by the sohd-state structure. P CODEX and variable temperature MAS NMR spectra confirmed that ionic conductivity is facihtated by dynamics at the bifurcated hydrogen bonds between anions, with a time scale of 57 4 ms at ambient temperature for rotation of the phosphonate about the C3V axis [51]. In the solid acid rubidium methane phosphonate (RMP) and the hydrated crystal RMP-2H20, they observed two different types of acidic protons as weU as the water protons in the lamella using H MAS NMR, and established... 

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