# Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application
## 4 Polymer-Inorganic Hybrids as Linkers  
Another well-defined category of organic-inorganic hybrids is metallosupramolecular complexes, which combine the functionalities of metal ions with organic ligands to form highly structured materials. The term \"metallosupramolecular chemistry\" was introduced by [PERSON] in 1994 to describe assemblies where metals act as a type of \"glue,\" holding together organic molecules through metal-ligand coordination [129]. Over the past few decades, this field has experienced exponential growth due to its ability to produce functional, stimuli-responsive materials with diverse applications. Metallosupramolecular polymers (MSPs) are a specific subset within this broader field, formed by the self-assembly of macromolecular monomers equipped with metal-binding motifs [52]. These materials utilize non-covalent interactions, including metal-ligand complexation, hydrogen bonding [130; 131], and host-guest interactions [131], which provide them with dynamic, adaptable properties. Because of the non-covalent nature of these interactions, MSPs are highly responsive to external stimuli, such as heat, light, chemicals, mechanical force, and electric or magnetic fields, allowing for temporary disassembly into monomeric units [132; 133]. This dynamic responsiveness supports functions such as self-healing, reversible adhesion, recycling, and easy reprocessing, making MSPs attractive for sustainable material design [49; 52; 134]. A comprehensive review of metallosupramolecular polymers is reported by [PERSON] et al. [135], which covers numerous examples in the field, including pioneering work by [PERSON] et al. [136]. In 1980, [PERSON] and colleagues presented one of the first studies on polymers with covalently attached bipyridines, aiming to develop a heterogeneous photocatalyst for solar-driven water decomposition. They synthesized these polymers by radical polymerization of a polystyrene backbone, followed by bromination, lithiation, and subsequent modification with bipyridine at various molar ratios (Figure 9a). To introduce ruthenium (Ru) into the polymer, they coordinated the bipyridine-modified polymer with [Ru(bpy)3]2+. This coordination endowed the polymer with photocatalytic properties, enabling it to absorb light and drive redox reactions essential for water splitting. One of the key features of MSPs is the metal-ligand interactions, which can vary significantly in strength depending on the specific metal and ligand involved. A notable class of ligands used in metallosupramolecular chemistry includes nitrogen-containing heterocyclic ligands, such as those with pyridine or imidazole units [129; 134]. These ligands are versatile and widely employed due to their ability to form stable complexes through their multiple donor atoms and the angular orientations of the metal-binding domains. An interesting example of this class of MSPs involves polymers containing a single bipyridine unit in the backbone. When metal ions are introduced to this bipyridine moiety, star-shaped polymer structures are formed. [PERSON] et al. [137] synthesized such polymers by substituting bipyridines on only one side with poly(ethylene oxide) or poly(propylene oxide) chains (Figure 9b), beginning with 4,4'-dimethylbipyridine. By reacting with LDA and subsequently adding an \(\alpha\)-alkyl ether-\(\omega\)-toylate polymer, they produced the desired structure, containing a single bipyridine unit. The addition of metal ions like Ni2+, Co2+, or Ru3+ resulted in star-shaped configurations, which were analyzed via UV/Vis spectroscopy and GPC. Notably, the Ru complexes exhibited stability under GPC shearing conditions, while the Ni2+ and Co2+ complexes dissociated. The architecture of metallosupramolecular assemblies can be controlled through ligand design. For example, linear coordination polymers, one of the simplest metallosupramolecular structures, are formed by combining linear bridging ligands with metals that provide 180\({}^{\circ}\) linkages, such as silver(I), palladium(II), or iron(III).