Their complexes with metal ions are called cryptates

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Unformatted text preview: ), the second number (4) tells us how many O atoms in the structure. Oxygen atoms are connected through –CH2CH2– bridges. A cryptand example O O N O O Crypt-[222] O O CHMB31H3 N Cryptands are polycyclic ligands that contain a cavity. Their complexes with metal ions are called cryptates (greek kryptos = hidden) Cryptand names. Crypt-[222] or 2,2,2-crypt: Three numbers (2, 2, 2) tell us how many oxygen atoms a cryptand has. All non-C atoms are connected via –CH2CH2– bridges. The Chemistry of Group 1 19 Examples of complexes [K(18-crown-6)]+ [K(crypt(222))]+ valinomycin CHMB31H3 The Chemistry of Group 1 20 Formation & Stability of Macrocyclic Complexes • A complex in aqueous solution is formed by substitution of coordinated water molecules (aquated cations) with other ligands. • The Group 1 cations bind water molecules only loosely (except Li+) and substitution is fast. • The stability of macrocyclic complexes depends on how well the cation fits in the ligand ring: N N O O O O O O O O O O N N CHMB31H3 O The Chemistry of Group 1 21 Liquid ammonia solutions • Gaseous ammonia can be easily converted in liquid state and used as a solvent -33 °C (239.6 K) NH3 (g) NH3 (l) • Similarly to water, liquid ammonia is a polar solvent that undergoes autoprotolysis: 2NH3 (l...
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