ABSTRACT
Organic molecules designed to bind cations selectively have been important components of metal ion detection systems. The crown ethers and derivatives (1–3), the paradigm of this molecular class, include ether oxygens as metal donor atoms and confer enhanced specificity by tailoring the cavity of the ligand to the optimal size and coordination number of the cation to be sequestered. The primary targets of crown ethers are mono and divalent alkali and alkaline earth cations and trivalent lanthanide ions. Crown ether complexes of transition metal ions are very rare, presumably because the donor capacity of a neutral oxygen atom to a transition metal atom is poor. Furthermore, while crown ethers are selective cation coordination compounds, they are not well suited for anion binding. In this contribution we provide an entry into a possible new class of sequestration agents called metallocrown ethers. These novel clusters are conceptually related to 9-crown-3 and 12-crown-4. A ring structure of ethereal like oxygen atoms are linked by two atom bridges of nitrogen and transition metal ions. This distinction leads to altered metal binding character and may provide an entry into selective anion detection agents.
