ANION RECOGNITION BY A DICOPPER(II) CRYPTATE

The dicopper(II) complex of the bistren cage 1, in an aqueous solution buffered at pH = 8, incorporates polyatomic anions (NCO-, NCS-, N-3(- ), SO42-, HCO3-, CH3COO-) according to a 1:1 stoichiometry. Log K valu es range over the 2-5 interval and show a sharp peak selectivity with respect to the anion 'bite', i.e. the distance between the two proxima te donor atoms of each anion. The peak maximum lies at about 2.3 Angst rom, a bite length corresponding to the N-3(-) anion. Thus, the dicopp er cryptate does not recognize anion size or coordinating tendencies, but simply recognizes the bite length. [GRAPHICS] ]