Drastic effects of the second coordination sphere on neutral vs. anionic guest binding to a biomimetic Cu(II) center embedded in a calix[6]aza-cryptand.

A calix[6]arene capped by a tmpa unit provides Cu(ii) funnel complexes that, for the first time, accept not only neutral guest ligands but also anionic ones such as a hydroxide, which is due to a small conformational change in the calixarene cone.