Thermally labile mono-alkyl phosphates and their alkali metal derivatives: synthesis and solid-state supramolecular aggregation

New organic-soluble mono-alkyl phosphate esters [(RO)P(O)(OH)₂] have been synthesized by esterification of phosphoric acid with the corresponding aliphatic alcohols in the presence of acetic anhydride. The products were initially isolated as cyclohexylamine salts, <i>viz.</i> [CyNH₃]₂[(CF₃CH₂O)PO₃]·H₂O (1) and [CyNH₃]₂[((CH₃)₃CCH₂O)PO₃]·H₂O·MeOH (3). Neutralization of these cyclohexylamine salts using a suitable ion exchange resin gave the corresponding phosphate esters [(RO)P(O)(OH)₂] (R = CF₃CH₂ (2); (CH₃)₃CCH₂ (4)). Reactivities of the trifluoroethyl phosphates 1 and 2 towards lithium and sodium ions have been explored and new alkali metal phosphate complexes [(CF₃CH₂OPO₃HLi)₃]_<i>n</i> (5), [(CF₃CH₂OPO₃HNa)₂]_<i>n</i> (6) and [CF₃CH₂OPO₃(Na_0.5)₂(CyNH₃)·(H₂O)₆]_<i>n</i> (7) have been isolated. Compounds 1-7 were characterized by different spectroscopic and analytical methods and their molecular structures were established by single-crystal X-ray diffraction studies. These alkyl phosphates and their complexes undergo diverse secondary interactions due to the presence of P-OH and PO groups, resulting in the formation of layered structures. The new alkali metal phosphates have been shown to be efficient single-source precursors to produce useful ceramic phosphates, such as LiPO₃, NaPO₃, and MCoPO₄ (M = Li and Na), through facile decomposition involving only gaseous by-products. This chemistry offers possibilities to generate other transition metal phosphates incorporating alkali metal ions, such as LiFePO₄, <i>etc</i>., which are used in energy storage devices and as electrocatalysts.