Solvent-Mediated Crystal-to-Crystal Interconversion between Discrete Lanthanide Complexes and One-Dimensional Coordination Polymers and Selective Sensing for Small Molecules

Two
isostructural 1D coordination polymers {[Ln­(OAc)2(H2O)­(OBPT)]·3H2O}n (HOBPT = 4,6-bis­(2-pyridyl)-1,3,5-triazin-2-ol, Ln = Eu3+, 1; Tb3+, 3) and two
discrete complexes [Ln­(OAc)2(DMF)2(OBPT)] (Ln
= Eu3+, 2; Tb3+, 4) have been synthesized in H2O–MeOH or DMF solvents,
respectively. Their structures were identified by powder X-ray diffraction.
Single-crystal X-ray studies for complexes 1 and 2 revealed that the coordination geometries of the Eu3+ ions are similar and can be described as a distorted tricapped
trigonal prism with six oxygen atoms and three nitrogen atoms. The
difference between them is that one aqua ligand and one oxygen atom
from the OBPT ligand complete the coordination sphere in complex 1, whereas two DMF molecules complete the coordination sphere
in complex 2. Interestingly, the solvent-mediated, reversible
crystal-to-crystal transformation between them was achieved by immersing
the crystalline samples in the corresponding solvent (H2O or DMF) or by exposing them to solvent vapor. Complex 1 shows a highly selective luminescence enhancement in response to
DMF in comparison to that observed in response to other examined solvents
such as acetone, ethyl acetate, ethanol, acetonitrile, methanol, and
THF.