Angular Dipyridyl Ligands 2,5-Bis(4-pyridyl)-1,3,4-oxadiazole and Its 3-Pyridyl Analogue as Building Blocks for Coordination Architectures: Assemblies, Structural Diversity, and Properties

The rational design and construction of functional coordination architectures, which rely upon the docile assemblages of organic ligands with metal centers, have attracted continuing interest for many years. The selection of suitable organic ligands as building blocks is a key point for the construction of novel coordination architectures with desired structures and functions. This article will briefly review the coordination-driven assembly of angular dipyridyl-type building blocks involving the oxadiazole spacer, namely 2,5-bis(4-pyridyl)-1,3,4-oxadiazole and its 3-pyridyl-donor analog 2,5-bis(3-pyridyl)-1,3,4-oxadiazole, with transition-metal ions. Diversity of the established structural motifs thus far (only considering the coordination interaction) is outlined, illustrating the broad range of coordination frameworks from discrete molecular architectures to infinite extended one-, two-, and three-dimensional (1-D, 2-D, and 3-D) networks. The specific influencing factors such as anion, solvent, and metal-to-ligand ratio on structural assemblies and the interesting properties of anion exchange, magnetism, fluorescence, and guest inclusion of these crystalline solids will also be discussed.