When lanthanide ions are present in the aqueous subphase of a floating monolayer (Langmuir film), the ions attracted to the interface will in many cases form commensurate and/or incommensurate two-dimensional structures. These lattices depend not only on the molecules forming the monolayer, but also on the atomic number of the lanthanide, with a sudden change between the lattice formed by lighter ions and that formed by heavier ions under a given monolayer. Since there are few other relevant differences between the lanthanides, we attribute the Z-dependent “transition” to the number of water molecules associated with each ion. The first hydration shell is thought to vary continuously from ∼9 in lighter lanthanides to ∼8 in heavier lanthanides.

Mitchell Miller1, Miaoqi Chu1, Binhua Lin2, Wei Bu2, and Pulak Dutta1

1Department of Physics & Astronomy, Northwestern University, Evanston, Illinois 60208, United States

2Center for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, United States

Langmuir, 2017, 33, pp 1412-1418

DOI: 10.1021/acs.langmuir.6b04609