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Linking molecular interactions to the macroscopic mechanical properties of soft materials remains a major challenge in soft-matter science. Here, we develop metal−polymer soft framework (MPF) ion gels, in which metal−ligand coordination complexes function as network-forming interchain bridges within a structurally homogeneous polymer network. Terpyridine-terminated TetraPEG prepolymers were cross-linked with divalent metal ions in an ionic liquid to form uniform coordinationbonded gel networks. The elastic modulus (G′) increased in the order Mg2+ < Zn2+ < Co2+ < Ni2+, and this trend was quantitatively reproduced by modeling the equilibrium distribution of bis-terpyridine complexes, M(tpy)2 2+, acting as network-forming interchain bridges in the polymer network. By integrating coordination thermodynamics with classical rubber elasticity, we established a quantitative framework that determines the stepwise equilibrium constants (K1 and K2) for mono and bis-terpyridine complex formation and accurately predicts the nonmonotonic dependence of G′ on metal-ion concentration. Furthermore, the stress relaxation time (τ) was found to increase with increasing coordination bond strength, indicating that the dynamic mechanical response is correlated with the strength of metal−ligand interactions. These results establish a quantitative framework linking coordination thermodynamics with macroscopic gel elasticity and further suggest that coordination interactions also play an important role in controlling the dynamic mechanical response, providing a basis for tuning the properties of coordination-bonded soft materials.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: ionic liquids, gels, ion gels, metal-ligand coordination, viscoelasticity, elasticity, supramolecular chemistry

Date published: 2026-06-09

Publisher: American Chemical Society (ACS)

Journal:

• Chemistry of Materials (ISSN: 08974756) vol. 38 issue. 11 p. 5723-5731

Funding:

• Japan Society for the Promotion of Science JP22H00340
• Japan Society for the Promotion of Science JP23H02030
• Japan Society for the Promotion of Science JP23H02066
• Japan Society for the Promotion of Science JP23K26723
• Japan Society for the Promotion of Science JP23K26759

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1021/acs.chemmater.6c00832

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Updated at: 2026-07-07 09:46:23 +0900

Published on MDR: 2026-07-07 12:25:14 +0900