A 2D Co(II) Coordination Polymer Containing Tri-flexural Helical Chains from Achiral Materials

A new ZnII metallocryptand with unprecedented diflexure helix induced by V-shaped diimidazole building blocks

Taking advantage of V-shaped ligands, a Zn^II metallocryptand, namely {[Zn₂(didp)₂(m-bdc)₂]}_n, (1) [didp = 2,8-di(1H-imidazol-1-yl)-dibenzothiophene and m-H₂bdc = isophthalic acid], has been hydrothermally synthesized. Single-crystal X-ray diffraction analysis reveals a 26-membered butterfly-type metallomacrocycle [Zn₂(didp)₂]. One m-bdc^2- ligand bridges [Zn₂(didp)₂] units to form a laterally non-symmetric [Zn₂(didp)₂(m-bdc)] metallocryptand with an exo-exo conformation. Another crystallographically independent m-bdc^2- functions as a secondary synthon to bridge discrete metallocryptands into a 1D zigzag chain architecture. Undoubtedly, the choice of two matched ligands in this work is crucial for metallocryptand construction and structure expansion. Interestingly, a rare helical chain with two flexures in one single L and/or R strand is observed. Another important feature is the C-O...π interactions, by which the dimensionality extension of (1) can be induced. Fluorescence measurements and density functional theory (DFT) calculations illustrate that the emission of (1) can probably be attributed to ligand-to-ligand charge transfer (LLCT).