Silver(I) and Thioether-bis(pyrazolyl)methane Ligands: The Correlation between Ligand Functionalization and Coordination Polymer Architecture

This work examines the crystal structures of 15 Ag(I) complexes with thioether functionalized bis(pyrazolyl)methane derivatives to rationalize the influence of the ligand on the formation of (a) coordination polymers (CPs), (b) oligonuclear (hexameric and dinuclear) complexes, and (c) mononuclear complexes. It was previously reported how this ligand class could generate microporous architectures with permanent porosity. Some ligand modifications could induce a cavity size modulation while preserving the same overall architecture. The bis(pyrazolyl)methane scaffold can be easily functionalized with various structural fragments; hence the structural outcomes were studied in this work using various ligand modifications and Ag(I) salts. In particular, six new ligand classes were prepared with the following features: (1) The steric hindrance on the pyrazole rings L3,3′Me, L5,5′Me, L5,3′Me, LCF3, and LBr was modified. (2) The steric hindrance was reduced on the peripheral thioether group: LSMe. (3) Finally, the presence of fluorine and bromine atoms in LCF3 and LBr offered the possibility to expand the type of interaction with respect to the ligands based on hydrocarbon substituents (CH3, phenyl, naphthyl). The effect of the anions was explored using different Ag(I) precursors such as AgPF6, AgBF4, AgCF3SO3, or AgNO3. A comparison of the crystal structures allowed for the tentative identification of the type of substituents able to induce the formation of CPs having permanent porosity to include a symmetric and moderate steric hindrance on the pyrazolyl moieties (four CH3) and an aromatic and preorganized thioether moiety. An asymmetric steric hindrance on the pyrazole groups led to the formation of more varied structural types. Overall, the most frequently reported structural motifs are the porous hexameric systems and the molecular chains.