Preparation and characterization of tetraaza[14]annulene and its nickel(II) and copper(II) complexes with crown ether functionalities

Three new organic hosts are described that contain a tetraaza[14]annulene core to which two crown ether voids are attached. These hosts include a free base tetraaza[14]annulene and/or its complexes with benzo-15-crown-5 rings. The crown tetraaza[14]annulene is synthesized from tetraaza[14]annulene and 4'-chloroformylbenzo-15-crown-5. Its nickel(II) and copper(II) complexes are prepared in a similar manner as above. In solution the compounds do not tend to form aggregates. However, aggregation is affected by the presence of alkali-metal salts, which coordinate to the crowns. Li+ and Na+ cations with diameters that match the diameters of the crown ether rings form 1:2 host-guest complexes. Complexes with 2:2 host-guest stoichiometry are formed when the diameters of K+ and Cs+ cations exceed that of the crown ether rings. Nevertheless, it is weak for the present macrocycle and its complexes to be inclined to form dimers owing to the steric hindrance of the substituent groups and owing to restraining the rotation of the carbonyl bond connecting the crown ether group.