Dynamic assembly deals with two or more self-assembled units, which are on a relatively flat potential energy surface and are interconverted into each other by the re-sorting or reorganization of the component species. [1][2][3] When dynamic structures have a cavity suitable for recognizing a guest, the predominant assembly of one particular host structure is induced by adding an appropriate guest. Such a guest-induced assembly of a specific host framework is often seen in biological events, and has been actively studied in both hydrogen-bonded and coordination assembly systems. [2] Here we report a unique dynamic assembly where, under a set of identical thermodynamic conditions, the same guest induces the formation of two different assemblies depending on whether the assembly process experiences crystallization or not.
The dynamic assembly discussed here stems from the {(en)Pd II } coordination block 1 (en = 1,2-ethanediamine) and ligand 2, which has four tripyridine podands on a benzenetetracarboxylate scaffold. [4] In an analogy with the guestinduced assembly of coordination nanotubes obtained from oligo(3,5-pyridine) ligands and Pd units, [5] ligand 2 is expected to yield the mono-end-capped coordination tube 3 12+ upon complexation with 1 in the presence of an appropriate guest (Scheme 1 a). [6] This tube is designed to differentiate between the ends of symmetrical rodlike molecules; namely, the end that is accommodated at the bottom of the tube should show different properties from the other end. We have found that, in addition to expected structure 3 12+ , the complexation of 1 and 2 also gives rise to the double open tube, 4 24+ , in which ligand 2 adopts an extended conformation (Scheme 1 b). This open tube is observed only at higher concentrations as a