Water Content-Controlled Formation and Transformation of Concomitant Pseudopolymorph Coordination Polymers

Area of Science:

• Coordination Chemistry
• Materials Science
• Crystallography

Background:

• Coordination polymers (CPs) are versatile materials with tunable structures and properties.
• Pseudopolymorphism, the existence of different crystalline forms of a compound due to variations in guest molecules, is crucial in CP design.
• Understanding solvent effects is key to controlling CP synthesis and polymorphism.

Purpose of the Study:

• To synthesize and characterize new concomitant pseudopolymorph coordination polymers.
• To investigate the role of solvent water content in the formation and transformation of cadmium-based CPs.
• To explore the structural interconversion between different CP phases.

Main Methods:

• Self-assembly synthesis of coordination polymers using cadmium acetate and a pyridyl-butadiene ligand (L).
• Single-crystal X-ray diffraction for structural determination of CPs.
• Analysis of solvent effects and environmental humidity on CP stability and transformation.

Main Results:

• Two 1D ladder pseudopolymorph coordination polymers, {[Cd2L2(OAc)4]·2DMSO} (1) and {[CdL(OAc)2]·2.75H2O} (2), were synthesized.
• The presence of water as an impurity in DMSO solvent led to the formation of concomitant pseudopolymorphs.
• Compound 1 transformed to a guest-free 1D linear compound (3') upon water absorption, and compound 3 transformed to compound 2 via dissolution-recrystallization.

Conclusions:

• Solvent water content actively controls the formation of specific coordination polymer phases (2 or 3).
• Environmental humidity influences the transformation of unstable pseudopolymorphic compounds.
• This study highlights a unique event of concomitant pseudopolymorph formation driven by trace water impurities.