Structural Diversity in Coordination Self-Assembled Networks of a Multimodal Ligand Azacalix[4]pyrazine

We report herein the synthesis of a new heteracalixaromatic
compound,
tetramethylazacalix[4]­pyrazine (TAPz), and its coordination
self-assemblies with metal and metal cluster centers. Structural characterization
of TAPz has shown that its conformation is fluxional
in solution but exhibits a dominant 1,3-alternate configuration in
the crystalline solid state, wherein its convergent chelating coordination sites are orthogonal to the 120°-angled bridging sites, thus forming
a unique multimodal ligand. Compound TAPz reacting with
silver, zinc metal centers, and CuxIx cluster centers leads to the construction
of diverse coordination network structures in 1–5 including honeycomb, Kagomé, α-quartz, and
cavity-involved two-dimensional layers. The structural diversity of
these network structures is conducted by different combination modes
between the chelation bonding sites of TAPz and metal
or metal cluster centers. This system may afford deeper insight on
the fantastic use of macrocyclic compounds on the designed synthesis
of coordination network structures through the proper arrangement
of their coordination sites.