What question did this study set out to answer?

This research aims to synthesize and characterize lanthanide-based coordination polymers featuring distinct structural types and their response to dehydration.

February 14, 2026

Series of Hydrated Lanthanide (La, Ce, Pr, Dy, Yb) Pyromellitate 3D Coordination Polymer with Tunnels Encapsulating Dimethylammonium Species and Its Crystal-to-Crystal Transformation upon Dehydration

Key Points

This research aims to synthesize and characterize lanthanide-based coordination polymers featuring distinct structural types and their response to dehydration.
Synthesize coordination polymers using btec ligands associated with lanthanides La, Ce, Pr, Dy, and Yb.
Characterize structural types via crystallography and analyze their interaction with water.
Examine the dehydration process and its impact on the structure of compound 1.
Apply GCMC calculations alongside water adsorption measurements to elucidate transformation mechanisms.
Two distinct coordination polymer structures were identified, one encapsulating dimethylammonium and water, the other encapsulating only dimethylammonium.
Dehydration of compound 1 resulted in a crystal-to-crystal transformation, forming a new phase with decreased cell volume.
The anhydrous phase showed reversible water adsorption capabilities, demonstrating structural flexibility.

Abstract

Synthesis and characterization of two distinct structural types of coordination polymers are reported with 1, 2, 4, 5-benzenetetracarboxylate (btec) ligands associated with lanthanides (Ln) Ce (III), La (III), and Pr (III) for compounds 1-3, and Dy (III) and Yb (III) for compounds 4-5. The two structures are built from the connection of lanthanide centers with the linkers to construct a 3D framework composed of 1D tunnels encapsulating dimethylammonium and water in (CH3) 2NH2Ln (btec) 00b72H2O (1-3) or dimethylammonium only in (CH3) 2NH2Ln (btec) (H2O) (4-5). These two atomic arrangements differ by the occurrence of infinite chains of edge-sharing LnO9 units and, the presence of trapped water species in 1-3, instead of dinuclear carboxylate-bridged 2 × LnO8 units and, bonded aquo species to Ln centers in 4-5. The dehydration process was investigated for compound 1. Removal of water induces a crystalline phase transition related to the shrinkage of the 3D network to form (Ln (btec) · (CH3) 2NH2, noted 1'). Elucidation of the mechanism is provided by combining water adsorption measurements with GCMC calculations. This transformation shows a relative flexibility of the network (cell volume variation of -6%) reminiscent of the breathing effect reported in the MOF such as the MIL-53 series. The anhydrous phase 1' is able to adsorb reversibly water as experienced with the measurement of water vapor isotherms.

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