Tuning of Polyoxopalladate Macroanionic Hydration Shell via Countercation Interaction

Abstract

Three types of macroanion-countercation interactions in dilute solution, decided by the strength of electrostatic attraction and the change of hydration shells are reported: minor interaction between macroanions [MO Pd (SeO ) ] (M=Zn or Ni ) and monovalent cations (Na , K , Rb , Cs ), leaving their hydration shells intact (solvent-separated ion-pairs); strong binding between macroanions and divalent cations (Sr , Ba ) to form solvent-shared ion-pairs with partial dehydration; very strong electrostatic attraction between macroanions and Y ion with contact ion-pairs formation by severely breaking their original hydration shells and forming new ones. In addition, divalent cations can help the macroanions self-assemble into hollow spherical blackberry structures through counterion-mediated attraction, whereas macroanions with mono- or trivalent cations only stay as discrete ions due to either weak interaction or a small number of bound countercations.

Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion

“…Divalent counterions have stronger electrostatic interaction with macroions. On the other hand, the energy cost is higher when they break their thicker hydration layer to closely associate with macroions [6b] . As most of the charges on {Mo 132 } are located inside its skeleton (30 acetate ligands), the longer charge separation distances weaken the electrostatic interaction, and the hydration effect becomes more important.…”

pH-induced phase transition and crystallization of soft-oxometalates (SOMs) into polyoxometalates (POMs): a study on crystallization from colloids

“…The surface tension, which plays an important role in nucleation, can be reduced by the addition of external heterogeneous seeds or templating agents which enhances the surface interaction, thus reducing the activation barrier for crystal formation (Galkin & Vekilov, 1999). In the literature, there have been several reports where templating effect of different cations, such as Na + , K + and Li + (Hayashi et al, 2015), and organic cations (He et al, 2018), and supramolecular interactions (Mascaros & Martí-Gastaldo, 2007) have played a decisive role in the isolation of POM clusters (Mü ller et al, 1991;Pradeep et al, 2010). Until now, nucleation of POMs have not been studied in the light of the two-step nucleation theory which encompasses the formation of a possible colloidal SOM phase.…”

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

“…Important to this Review, residing between the POMs on the blackberry surface there must be counter‐cations, otherwise the repulsive electrostatic interactions between neighboring POMs would overwhelm any attractive forces. Blackberry formation only occurs in dilute solutions ([POM] ≈0.1–10′s of mg mL −1 ), and their formation can be triggered by time, addition of a less polar solvent, or addition of counter‐cations with low hydration energy (Rb + , Cs + ) or high charge (Mg 2+ /Ca 2+ /Sr 2+ /Ba 2+ , Al 3+ , Y 3+ ). These cations are effective because they can undergo strong contact ion‐pairing with POMs in solution (see Section 1.3), which is the first step towards blackberry formation.…”