One- and Two-Step Self-Assembly Processes in Zn(II) Supramolecular Frameworks with Ditopic Bis(pyrazolyl)methane Ligands. Chiral Recognition and Formation of Cyclic Helicates

摘要

The new ligands bis(pyrazol-1-yl)(pyridine-3-yl)methane (bpzm3py, 1) and bis(3,5-dimethylpyrazol-1-yl)(pyridine-3-yl)methane (bpz*m3py, 2) have been synthesized. Box-like cyclic dimers have been obtained by reaction of the ligands with Zn(NO3)(2), namely, [Zn-(NO3)(2)L](2) (L = 1, complex 3; L = 2, complex 4), after the self-assembly of two metal centers and two ligands in a head-to-tail fashion. In 3 and 4 the pyridine rings exhibit planar chirality and the two pR,pR and pS,pS enantiomers coexist in the crystal. A two-step self-assembly process using 3 as an SBU and sodium 1,4-benzenedicarboxylate (Na2BDC) as a linker leads to the formation of hexanuclear cyclic helicates with a distorted trigonal prism form [Zn-2(BDC)(1)(2)(H2O)(4)](3)(BDC)(3) (5) constituted by cyclic dimers and mu(2),kappa(2)-BDC connectors that are oriented diagonally. The chiral recognition that is observed means that the three dimers of the helicate have the same chirality. In the 3-D structure, chains of helicates of the same chirality are formed and these interdigitate with chains of opposite chirality connected by hydrogen bonds and through a column of pi-pi stacking interactions involving alternate pyridine and benzene rings.