s-Tetrazines, six-membered aromatic heterocycles with four nitrogen, have extremely deficient π- electron system and are enable to sustain efficient attraction for polarized atoms or anions. In the view of coordination chemistry of s-tetrazines, their poor π-electron densities and multi coordination sites lead the structural diversity of coordination complexes depending on counter anions and electron rich guest molecules.
In this study, a series of coordination polymers which consist of s-tetrazine ligands and silver(I) ions were synthesized and their structural diversity depending on counter anions were analyzed by single crystal X-ray diffractions. Furthermore two novel tetraruthenocycles containing structural isomers of bipyridyl-s-tetrazines (p-PTTz and m-PTTz) were synthesized and characterized by 1H NMR and elemental analysis. The molecular structures of these ruthenocycles are determined by single crystal X-ray diffraction study. The structures of (p-PTTz-Ru and (m-PTTz-Ru exhibit rectangular shaped macrocycles with nano pores of 13 X 8 Å and 15 X 8 Å respectively, and their structural features were determined by the geometrical differences between p-PTTz and m-PTTz. These cavities are large enough to encapsulate polyaromatic molecules like anthracene, pyrene and phenanthrene. Especially extremely poor π-electron density of s-tetrazine rings affected efficient binding affinity of ruthenocycles with aromatic guest molecules through donor acceptor interactions. The binding constants between ruthenocycles and polyaromatic guests were measured by 1H NMR in d6-acetone.
The structural diversity of s-tetrazine Ag(I) coordination polymers depending on the nature of anion and the trend of binding constants between ruthenocycles and π -aromatic guests will be presented.
Figure 1. 3D structures of p-PTTz-Ru and m-PTTz-Ru