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, viz. [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]n (5), [(CF3CH2OPO3HNa)2]n (6) and [CF3CH2OPO3(Na0.5)2(CyNH3)·(H2O)6]n (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, etc., which are used in energy storage devices and as electrocatalysts.