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

Abstract

New organic-soluble monoalkyl 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 the cyclohexylamine salts, viz. [CyNH3]2[(CF3CH2O)PO3]H2O (1) and [CyNH3]2[((CH3)3CCH2O)PO3]H2OMeOH (3). Neutralization of these cyclohexylamine salts by a suitable ion exchange resin gave the corresponding phosphates esters [(RO)P(O)(OH)2] (R = CF3CH2 (2); (CH3)3CCH2 (4). Reactivity of the trifluoroethyl phosphates 1 and 2 towards lithium and sodium ions have been explored and new alkali metal phosphate complexes [(CF3CH2PO4HLi)3]n (5), [(CF3CH2PO4HNa)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 to result 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 is expandable to generate other transition metal phosphates incorporating alkali metal ions such as LiFePO¬4 etc.