C&EN: TODAY'S HEADLINES - IONIC LIQUID YIELDS NETWORK

MICHAEL FREEMANTLE

The discovery that room-temperature ionic liquids can be used as solvents to prepare extended networks of coordination complexes could lead to another potentially useful application of these materials.

Using a thermally stable and poorly coordinating ionic liquid as a solvent, chemistry professors Jing Li at Rutgers University and Scot Wherland at Washington State University and coworkers synthesized a crystalline copper-containing complex with a two-dimensional wavelike structure that resembles a brick wall [Chem. Commun., 2002, 2872].

Li and colleagues prepared the coordination complex—[Cu(I)(bpp)]BF4—by the reaction of Cu(NO₃)2*3H₂O with 1,3-bis(4-pyridyl)propane (bpp) using 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as solvent.

“The low solubility of coordination polymers means that their isolation as single crystals and subsequent structural characterization has been somewhat hindered,” remarks coordination polymer expert Michael J. Zaworotko, a chemistry professor at the University of South Florida. The use of ionic liquids, he says, represents a new and potentially broad-ranging methodology that should be applicable to a wide range of metals and ligands.

Ionic liquids have a number of advantages over organic solvents, including high thermal stability, low volatility, and the ability to be tailored to meet specific synthetic needs, Li points out. In addition, “the special nature of the ionic liquid leads to different structures compared with those obtained by other routes,” explains ionic liquids expert Peter Wasserscheid, a chemistry lecturer at Rhine-Westphalia Technical University (RWTH), Aachen, Germany.

“The current work signifies the beginning of our efforts in exploring this area,” Li tells C&EN. Now, she explains, “We will conduct an extensive study to investigate the applicability of ionic liquids in the synthesis of coordination network structures in general.”