page_title: 15-Crown-5
section_title: Properties
hierarchical_section_title: 15-Crown-5 / Properties
caption_attribution_description: English: Structure of the complex between the oxonium ion H7O3+ and 15-crown-5
context_page_description: 15-Crown-5 is a crown ether with the formula (C₂H₄O)₅. It is a cyclic pentamer of ethylene oxide that forms complex with various cations, including sodium and potassium, however, it is complementary to Na⁺ and thus has a higher selectivity for Na⁺ ions.
context_section_description: Analogous to 18-crown-6, 15-crown-5 binds to sodium ions.  Thus, when treated with this complexing agent, sodium salts often become soluble in organic solvents.
  First-row transition metal dications fit snugly inside the cavity of 15-crown-5.  They are too small to be included in 18-crown-6. The binding of transition metal cations results in multiple hydrogen-bonded interactions from both equatorial and axial aqua ligands, such that highly crystalline solid-state supramolecular polymers can be isolated. Metal salts isolated in this form include Co(ClO₄)₂, Ni(ClO₄)₂, Cu(ClO₄)₂, and Zn(ClO₄)₂. Seven coordinate species are most common for transition metal ions complexes of 15-crown-5, with the crown ether occupying the equatorial plane, along with 2 axial aqua ligands.
  15-crown-5 has also been used to isolate salts of oxonium ions. For example, from a solution of tetrachloroauric acid, the oxonium ion [H₇O₃]⁺ has been isolated as the salt [(H₇O₃)(15-crown-5)₂][AuCl₄]. Neutron diffraction studies revealed a sandwich structure, which shows a chain of water with remarkably long O-H bond (1.12 Å) in the acidic proton, but with a very short OH•••O distance (1.32 Å).
  A derivative of 15-crown-5, benzo-15-crown-5, has been used to produce anionic complexes of carbido ligands as their [K(benzo-15-crown-5)₂]⁺ salts:
  (Ar₂N)₃MoCH  +  KCH₂Ph  +  2 (15-crown-5)   →   [K(15-crown-5)₂]⁺[(Ar₂N)₃MoC]⁻  + CH₃Ph
caption: Structure of [(H7O3)(15-crown-5)2]+ ion
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