Self-Assembly of Silver(I) and Ditopic Heteroscorpionate Ligands. Spontaneous Chiral Resolution in Helices and Sequence Isomerism in Coordination Polymers

The self-assembly of the ligands bis(pyrazol-1-yl) (pyridine-4-yl)methane (L-1) and bis(3,S-dimethylpyrazol-1-yl) (pyridine-4-yl)methane (L-2) with AgBF4 leads to three types of species: L-1 gives rise to the formation of a boxlike cyclic dimer (1) while L-2 leads to two different coordination polymers that are sequence isomers. With dependence on the crystallization conditions, either a homochiral helix (2) with spontaneous resolution or a zigzag polymer is formed (3). By means of solid-state circular dichroism studies, the presence of both enantiomers in 2 is observed, enriched locally in colonies of crystals. The homochiral motif is stable, even upon removal of guest solvent molecules. The noncovalent interactions in the crystalline structure are clearly affected by the presence of the methyl groups on the pyrazolyl rings. The behavior of the compounds in solution is discussed.