Discrete metallocyclic complexes based on rigid pyrazole-containing ligands as building blocks to construct inorganic–organic supramolecular assemblies through the second interactions

Utilizing the new rigid bidentate pyrazole-containing ligands 1,3-bis(1-pyrazolyl)benzene (bpb) and 3,5-bis(1-pyrazolyl)phenylmethanol (bppm) with corresponding silver salts, four new compounds, [Ag2(bpb)2(NO3)2] (1), [Ag2(bpb)2(OSO2CF3)2] (2), {[Ag2(bpb)2](BF4)2} (3), and [Ag2(bppm)2(NO3)2] (4), have been synthesized. X-ray diffraction analyses reveal that these compounds involve the discrete M2L2-type metallocyclic units, which serve as building blocks to further expand to various three-dimensional inorganic–organic supramolecular assemblies through the second interactions such as hydrogen bonds (e.g., O–H⋯O, C–H⋯O and C–H⋯F), π⋯π stacking and C–F⋯π interactions. Especially in compound 1, the metallocyclic units are directly connected by Ag–O–Ag bonds, which constitutes, to the best of our knowledge, the first example of inorganic–organic hybrid polymers with channels bridged by oxygen atoms from inorganic anions. Unlike 1–4, the usage of 2,7-bis(1-pyrazolyl)naphthalene (bpn) results in the formation of one-dimensional zigzag coordination polymer chains [Ag(bpn)NO3] (5) rather than the discrete metallocyclic structures, which are further bridged by nitrate anions to generate an unusual (4,4) 2-D sheet structure with quadrangle grids. The structural differences of five compounds mainly depend on the nature of organic ligands and anions. These results demonstrate that the second interactions could play important roles in the aspect of linking low-dimensional entities into high-dimensional supramolecular frameworks.