Supramolecular Structure of <i>N</i>,<i>N</i>-Bis(2-hydroxybenzyl)alkylamine: Flexible Molecular Assembly Framework for Host without Guest and Host with Guest

N,N-Bis(2-hydroxybenzyl)alkylamine derivatives form a cage-like assembly consisting of two molecules via inter- and intramolecular hydrogen bonds. The derivatives exhibit themselves as host to accept copper-ion guests under the double-oxygen-bridged dimeric system. Quantum chemical calculation suggested that the host−guest interaction is based on a charge-transfer coordination. Comparison of the crystal structures before and after complexation clarifies a rare example of a host−guest compound where the hosts maintain their cage framework through the change of hydrogen bonds to coordination bonds.