Dendritic Pyridine-Functionalized Polyesters and Their Polycationic Hydrogen Bonded Picrates:  Synthesis and X-ray Structural Study of Weak Hydrogen Bonding

Nicotinato and isonicotinato functionalized pentaerythritol and dipentaerythritol dendritic polyester compounds were synthesized. The compounds were crystallized, and the single-crystal structures were determined. Protonation by picric acid produced charged dendritic polyesters. Analysis of the role of weak hydrogen bonding CH···π and π···π interactions in the solid state was performed and compared to the corresponding benzoxy analogues which were also synthesized. The tetranicotinate 3b and tetrabenzoate 4 were found to have analogous structures, which in turn differ from the structure of the tetraisonicotinate 3c. The difference is attributed to the crucial role of CH···O and CH···N hydrogen bonding networks between the layers in the crystal lattice. The layers are held together by intermolecular CH···π and π···π interactions. The compound 3c formed an intertwined, tetrahedral network due to the acceptor ability of the aromatic nitrogen in the para position of the compound. Compound 9c exhibited an incomplete protonation by picric acid. Of six available aromatic nitrogens, only five were protonated.