No abstract

Although ammonium nitrate is at best sparingly soluble in typical organic solvents, it may be readily solubilized through the addition of chelating agents such as crown ethers and polyethylene glycols. With suitable choice of solvent and chelating agent, addition of a precipitating solvent leads to the crystallization of uncomplexed ammonium nitrate from such solutions. Crystalline ammonium nitrate obtained through this process of "complexation-mediated crystallization" displays a variety of morphologies, with the crystal form dependent on the nature of both the solvent and the chelating agent.

structure structure (organic substances) K 9000 -025Hydration, Ion Pairing, and Sandwich Motifs in Ammonium Nitrate Complexes of Crown Ethers.-Ammonium nitrate coordinates to 18-crown-6 to form a complex of 1:1 stoichiometry through a near-ideal 'tripod' arrangement of hydrogen bonds to alternate crown ether oxygen atoms. An additional bonding interaction between the crown ether-bound ammonium ion and the counterion is influenced by the extent of hydration, relatively insignificant in aqueous solution, but significant in anhydrous media. Hence it follows that water plays a potentially significant role in dictating the structural details of cation-crown ether complexes. In contrast, ammonium nitrate forms complexes with 15-crown-5 and benzo-15-crown-5 of 1:2 stoichiometry which show sandwich-type structure, with the ammonium cation complexed between two roughly parallel crown ether rings. -(DOXSEE, KENNETH M.; FRANCIS JR., PERRY E.; WEAKLEY, TIMOTHY J. R.; Tetrahedron 56 (2000) 36, 6683-6691; Dep. Chem., Univ. Oreg., Eugene, OR 97403, USA; EN)