Counter-ion association effect in dilute giant polyoxometalate [(As12CeIII)-Ce-III (16)(H2O)(36)W148O524](76-)({W-148}) and [Mo132O372(CH3COO)(30) (H2O)(72)](42-)({Mo-132}) macroanionic solutions

摘要

This article reports the use of simple conductivity measurements to explore the state of small counter-ions (mostly NH4+ and Na+) in [(As12Ce16III)-Ce-III(H2O)(36) W(148)O524](76-) ({W-148}) and [MO132O372(CH3COO)(30)(H2O)(72)](42)- ({MO132}) macroanionic solutions. All the solutions are dialyzed to remove the extra electrolytes. Conductivity measurements on {(NH4)(70)Na6W148} and {(NH4)(42)Mo-132} solutions at different concentrations both before and after dialysis indicate that the state of counter-ions has obvious concentration dependence. The "counter-ion association" phenomenon, that is, some small counter-ions closely associate with macroartions and move together, has been observed in both types of macroionic solutions above certain concentration. The association of counter-ions in hydrophilic macroionic solutions provides support on our previous speculation that the counter-ions might be responsible for the unique self-assembly of such macroanions into single-layer blackberry-type structures.