Alkali Metal Ion-exchange in a Metal-Organic Framework Based on Lanthanum and 1,4-Phenylenebis(methylidyne)tetrakis(phosphonic acid).

The ion-exchange selectivity of four metal-organic frameworks (denoted as MLaL), formed by alkali metal ions (M+), La3+, and 1,4-phenylenebis(methylidyne)tetrakis(phosphonic acid) (L), was examined. Unusual selectivity for the alkali metal ions was observed, which did not follow the previously proposed mechanism that was explained based on the ion-size similarity in the framework. The changes in the crystal structures after ion-exchange reactions were observed by powder X-ray diffraction analysis. The change in the lattice energy in a mixed-metal framework is likely to be one of the significant parameters to affect ion-exchange selectivity.

Transmetalation in a Ce(III)-phosphoester Crystalline Coordination Polymer with an Exceptionally High Selectivity for Yb(III) and Lu(III).

A novel crystalline coordination polymer containing Ce3+ and bis(4-nitrophenyl) phosphate (L), CeL3 , was synthesized and its unique transmetalation selectivities toward Yb3+ and Lu3+ in the lanthanide series were evaluated. The relatively large difference in transmetalation selectivity between the neighboring Tm3+ and Yb3+ species is noteworthy because the reactivities of heavy lanthanides are generally considerably similar. The structural strain of the polymeric framework is likely responsible for this unusual trend. Powder X-ray diffraction analysis indicated that, in the cases of only Yb3+ and Lu3+ , large differences in their ionic sizes compared to that of Ce3+ in the parent framework may induce a structural strain after solid solution formation, while cleavage of the relatively weak Ce-O bond allows the formation of new Yb-O and Lu-O bonds with the incoming Yb3+ and Lu3+ , respectively. Structural phase transitions likely caused by the heterogeneous nucleation of the Yb- (or Lu-) type phase were also observed.