A study on controlling structural topologies in coordination networks: solvent-directed synthesis and distinct variations in optical properties

Abstract

Investigating the correlation between structural diversity and functionality serves as a pivotal factor in propelling the progress of functional materials, which however commonly needs tedious synthesis or sophisticated screening of conditions. Herein, we establish a facile strategy to synthesize two series of coordination networks (CNs, i.e., Ln-CMNDI and LN-CMNDI-F) with two distinct topologies using a solvent-directed method employing a specific ligand N,N′-bis(carboxymethyl)-1,4,5,8-naphthalenediimide (H₂CMNDI) and rare-earth metal ions. The single-crystal X-ray diffraction analysis shows that Ln-CMNDI-F (Ln = La, Pr, Sm, Tb, Dy, Eu, Yb) synthesized using DMF and H₂O as the solvents adopt a two-dimensional planar structure, while Ln-CMNDI (Ln= Ho, Gd, Tb, Yb, La and Eu) with three-dimensional supramolecular structures are obtained under the same conditions due to the existence of hydrogen bonding between molecules when DMF is replaced with DMA. The topology type of Ln-CMNDI-F is assigned as lcf (abbreviation of Ln-CMNDI-F) and the topological type of Ln-CMNDI is assigned as lcn (abbreviation of Ln-CMNDI) which are both not collected in the RCSR. Moreover, such differences in the changes of the topological structures lead to different optical properties including photochromism properties and fluorescence sensing abilities. The photochromism property of Ln-CMNDI-F is superior to that of Ln-CMNDI in terms of the speed of photoresponse. However, Ln-CMNDI exhibits a better performance in fluorescence sensing towards nitrophenols. This work reveals that Ln-CMNDI and Ln-CMNDI-F with novel topological structures can be constructed by adjusting the solvent reasonably, providing insights for the construction of CNs with promising optical applications.