Two chiral cadmium carboxylate framework isomers generated by spontaneous resolution: synthesis, structures and properties

Abstract

Two three-dimensional (3-D) chiral coordination polymers, [Cd(NDC)(DMF)]_n (1_L and 1_D: H₂NDC = 1,4-naphthalenedicarboxylic acid and DMF = N,N′-dimethylformamide), have been synthesized by introducing the rigid achiral dicarboxylic acid ligand under solvo-thermal conditions, without chiral template or additives. Both chiral Cd-CPs were characterized by single crystal X-ray crystallography, and structural analysis indicates that 1_L and 1_D are enantiomers based on the zigzag [Cd(COO)₂(DMF)]_n rod secondary building units, featuring the left- or right-hand 2₁ Cd-O-C-O-Cd helix chains and left- or right-hand 4₁ screw [Cd(NDC)]_n columns, respectively. The FT-IR, TGA, powder X-ray diffraction and solid-state luminescence of 1 have been investigated. It is intriguing that the evidence from the circular dichroism spectroscopies confirms enantiomeric excess in the whole spontaneous resolution crystallization.

Graphical Abstract

Keywords:

• Cadmium
• chiral coordination polymer
• helix chain
• luminescent
• circular dichroism

Acknowledgements

The authors would like to thank anonymous referees for helpful discussions on crystal structures.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was financially supported by the National Science Foundation of China (Grant No.11375082), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (for Dr. X.-F. Wang), the NSF of Hunan Province (Grant No.2016JJ3105) and the Research Foundation of Education Bureau of Hunan Province (15B200 and17C1358).