Metal Ion and Anion-Based Tuning of a Supramolecular Metallogel

A bis(pyridylurea) ligand (1) forms metallogels in methanol in the presence of up to 0.5 equiv of copper(II) chloride. The metallogel has been characterized using powder X-ray diffraction, SEM, and MAS NMR spectroscopic techniques. The addition of further copper(II) chloride gives the unusual crystalline 4:3 coordination polymer [Cu-3(1)(4)Cl-4]Cl-2 center dot nH(2)O (2). In the presence of 0.5 equiv of copper(II) nitrate, the 2:1 crystalline coordination polymer [Cu(1)(2)](NO3)(2)center dot H2O center dot MeOH (5) is isolated. Both 2 and 5 have been characterized by single-crystal X-ray diffraction. Complex 5 represents a possible model for the gelator and highlights key interactions with counteranions that suggest a means to tune gel properties using anion binding. The influence of chloride and acetate anions (as their NBu4+ salts) on the rheological properties of the copper(II) chloride metallogels of 1 are investigated. The rheology of the anion-containing mixtures shows complex behavior with the gel structure apparently evolving over time.