Composites of N,N′-bis-(pyridyl) urea-dicarboxylic acid as new hydrogelators—a crystal engineering approach

Sixteen composites of a hydrogelator N,N′-bis(4-pyridyl) urea 1 and a nongelator N,N′-bis(3-pyridyl) urea 2 with a series of dicarboxylic acids having various backbones have been prepared and characterized. Seven such composites—three from the composites of 1 and four from the composites of 2—turned out to be good to moderate gelling agents for pure water. Single crystal X-ray structures of three such gelators and four nongelators indicate that microporosity in the crystalline solid state structure may be one of the important criteria for hydrogelation.