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.

两种同构一维配位聚合物{[Ln(OAc)₂(H₂O)(OBPT)]·3H₂O}ₙ（其中HOBPT为4,6-双(2-吡啶基)-1,3,5-三嗪-2-醇，Ln分别为Eu³⁺对应化合物1、Tb³⁺对应化合物3）与两种离散型配合物[Ln(OAc)₂(DMF)₂(OBPT)]（Ln分别为Eu³⁺对应化合物2、Tb³⁺对应化合物4），分别在水-甲醇（H₂O-MeOH）混合溶剂与N,N-二甲基甲酰胺（DMF）中合成。所有目标配合物的结构均通过粉末X射线衍射予以表征。对化合物1与2的单晶X射线衍射分析显示，Eu³⁺离子的配位几何构型相近，均可被描述为包含6个氧原子与3个氮原子的畸变三帽三角棱柱构型。二者的差异在于：化合物1的Eu³⁺配位球由1个配位水分子与1个OBPT配体提供的氧原子完成配位，而化合物2的配位球则由2个DMF分子完成配位。值得注意的是，通过将晶体样品浸泡于对应溶剂（H₂O或DMF）中，或将其暴露于对应溶剂蒸气环境下，可实现二者之间溶剂介导的可逆晶态-晶态转变。与丙酮、乙酸乙酯、乙醇、乙腈、甲醇及四氢呋喃（THF）等其他受试溶剂相比，化合物1对DMF展现出极高选择性的荧光增强响应。