Complexes of ytterbium(III) nitrate and triflate with homoazacalix[n]arenes (n=3, 4)

The synthesis and crystal structures of three ytterbium(III) complexes of homoazacalixarenes are reported. In all cases, the complexes are obtained without addition of a base, the protons of the complexing phenolic moieties being transferred to the amine groups upon complexation. The 1:1 complex between p-chloro-N-benzylhexahomotriazacalix3]arene (1) and Yb(NO₃)₃ is analogous to the neodymium(III) complex reported previously, with the metal ion bound to three phenoxide groups and three nitrate ions. A second 1:1 complex is obtained with Yb(NO₃)₃ and p-methyl-N-benzyltetrahomodiazacalix4]arene (2), in which the metal ion is bound to two phenoxide groups only. The replacement of nitrate by triflate counter-ions results in the formation of a 1:2 ‘sandwich’ complex with 1, in which two divergent calixarene molecules are bridged by the metal ion, the counter-ions being non-bonding.