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1. Metals in polymers: hybridization enables new functions

   https://doi.org/10.1039/d0tc03810e  

   Wei, Zichao; Duan, Hanyi; Weng, Gengsheng; He, Jie (November 2020, Journal of Materials Chemistry C)

   null (Ed.)

   Adding metals into synthetic polymers is of broad interest to design multifunctional materials, particularly harnessing unique properties and functionalities not found in pure organic polymers. Other than simple emergence of the two, such hybridization often enables synergies to amplify the existing properties and/or create new properties not existing in either component. In this review, we highlight recent examples of metal/polymer hybrids based on either well-defined or ill-defined metal–ligand (M–L) coordination to design multifunctional materials. This review describes how in the hybridization of metal ions and polymers they complement each other synergistically in terms of their optical, mechanical and catalytic functionalities. Synthetic polymers once bound to metals enable stimuli-responsive properties of the metals and control over the luminescence of the metals in response to a change in the environment. As the second coordination sphere, synthetic polymers also enhance the reactivity of metal sites as a means to design bioinspired artificial enzymes. Additionally, the impact of the M–L coordination on the dynamic properties of polymers is summarized in the context of self-healable and tough materials built on the reversible network of interchangeable M–L coordination. 

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2. Molecular chains of coordinated dimolybdenum isonicotinate paddlewheel clusters

   https://doi.org/10.1039/C9RA03572A  

   Li, Minyuan M.; Claire, F. James; Solomos, Marina A.; Tenney, Stephanie M.; Ivanov, Sergei A.; Siegler, Maxime A.; Kempa, Thomas J. (May 2019, RSC Advances)

   A growing focus on the use of coordination polymers for active device applications motivates the search for candidate materials with integrated and optimized charge transport modes. We show herein the synthesis of a linear coordination polymer comprised of Mo 2 (INA) 4 (INA = isonicotinate) metal–organic clusters. Single-crystal X-ray structure determination shows that this cluster crystallizes into one-dimensional molecular chains, whose INA-linked Mo 2 cores engage in alternate axial and equatorial binding motifs along the chain axis. Electron paramagnetic resonance spectra, absorption spectra, and density functional theory calculations show that the aforementioned linear coordination environment significantly modifies the electronic structure of the clusters. This work expands the synthetic foundation for assembly of coordination polymers with tailorable dimensionalities and charge transport properties. 

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3. Synthesis and disassembly of an organometallic polymer comprising redox-active Co ₄ S ₄ clusters and Janus biscarbene linkers

   https://doi.org/10.1039/d2cc00953f  

   Gillen, Jonathan H.; Moore, Connor A.; Vuong, My; Shajahan, Juvairia; Anstey, Mitchell R.; Alston, Jeffrey R.; Bejger, Christopher M. (April 2022, Chemical Communications)

   Here, we show for the first time that main-chain organometallic polymers (MCOPs) can be prepared from Janus N-heterocyclic carbene (NHC) linkers and polynuclear cluster nodes. The crosslinked framework Co 4 S 4 -MCOP is synthesized via ligand displacement reactions and undergoes reversible electron transfer in the solid state. Discrete molecular cluster species can be excised from the framework by digesting the solid in solutions of excess monocarbene. Finally, we demonstrate a synthetic route to monodisperse framework particles via coordination modulation. 

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4. Adaptable Eu-containing polymeric films with dynamic control of mechanical properties in response to moisture

   https://doi.org/10.1039/c9sm02440a  

   Wei, Zichao; Thanneeru, Srinivas; Margaret Rodriguez, Elena; Weng, Gengsheng; He, Jie (March 2020, Soft Matter)

   Self-healing polymers often have a trade-off between healing efficiency and mechanical stiffness. Stiff polymers that sacrifice their chain mobility are slow to repair upon mechanical failure. We herein report adaptable polymer films with dynamically moisture-controlled mechanical and optical properties, therefore having tunable self-healing efficiency. The design of the polymer film is based on the coordination of europium (Eu) with dipicolylamine (DPA)-containing random copolymers of poly( n -butyl acrylate- co -2-hydroxy-3-dipicolylamino methacrylate) (P( n BA- co -GMADPA)). The Eu–DPA complexation results in the formation of mechanically robust polymer films. The coordination of Eu–DPA has proven to be moisture-switchable given the preferential coordination of lanthanide metals to O over N, using nuclear magnetic resonance and fluorescence spectroscopy. Water competing with DPA to bind Eu 3+ ions can weaken the cross-linking networks formed by Eu–DPA coordination, leading to the increase of chain mobility. The in situ dynamic mechanical analysis and ex situ rheological studies confirm that the viscofluid and the elastic solid states of Eu-polymers are switchable by moisture. Water speeds up the self-healing of the polymer film by roughly 100 times; while it can be removed after healing to recover the original mechanical stiffness of polymers. 

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5. N-Heterocyclic carbene-ended polymers as surface ligands of plasmonic metal nanoparticles

   https://doi.org/10.1039/c9tc04776j  

   Thanneeru, Srinivas; Ayers, Kaitlynn M.; Anuganti, Murali; Zhang, Lei; Kumar, Challa V.; Ung, Gaël; He, Jie (February 2020, Journal of Materials Chemistry C)

   A facile methodology to prepare N-heterocyclic carbene (NHC)-terminated polymers as surface ligands to functionalize gold nanoparticles (AuNPs) is reported. Our method highlights a mild, aerobic synthesis of NHC-functionalized polymers and a simple ligand exchange approach towards surface modification of AuNPs prepared in aqueous solution. Two methods, including end-group functionalization of halogen-ended polymers from a conventional atom transfer radical polymerization (ATRP) and post-polymerization functionalization of imidazole-containing polymers using imidazole-containing ATRP initiator, have been investigated to prepare imidazolium-ended polymers. Using a one-step, oxygen and moisture tolerant procedure, the polymer–NHC–Cu( i ) species can be synthesized from imidazolium-ended polymers and readily bind to citrate-capped AuNPs likely through transmetalation, yielding robust polymer-stabilized AuNPs. Our synthetic method significantly simplifies the preparation and use of polymer–NHC ligands for surface functionalization of metal NPs. Our methodology is general and potentially applicable to any polymers prepared by ATRP to functionalize metal NPs via NHC–metal coordination; therefore, it will likely broaden the applications of polymer–NHC ligands for metal nanoparticles in the fields of catalysis and nanomedicine. 

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