# Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application
## 4 Polymer-Inorganic Hybrids as Linkers
### Coordination Polymers (CPs) and Metal-Organic Frameworks (MOFs)  
Coordination polymers are metal-ligand coordination compounds that form one-dimensional (1D) extended chains, two-dimensional (2D) sheets, or three-dimensional (3D) frameworks [138]. The dimensionality of CPs exhibits considerable variation, ranging from linear chains to intricate flexible networks. The use of flexible ligands with rotatable covalent bonds, involving sp\({}^{3}\) hybrid atoms, like carbon, oxygen, or nitrogen, allows for a wide range of conformations during the self-assembly process. For example, a recent study showed that a zinc-cystine coordination polymer can self-assemble into a 3D structure resembling chloroplasts, combining light-harvesting and catalytic functions for sustainable fuel production (Figure 10a) [139]. CPs have also demonstrated promising applications in biomedicine due to their versatility and multifunctionality. These applications span drug delivery, bioimaging, and biosensing applications. Nanoscale coordination polymer particles (CPPs), for example, can encapsulate therapeutic agents, protecting drugs from degradation and minimizing side effects while also enabling targeted delivery to cancer cells [140]. Figure 10: (**a**) (**i**) SEM image of Cys(Zn) microspheres obtained from the assembly of cystine (2 mm) and ZnCl\({}_{2}\) (2 mm) at pH 8.0. (**ii**) Enlarged SEM image of the edge of a Cys(Zn) microsphere. (**iii**) SEM image of a section of a Cys(Zn) microsphere. (**iv**) TEM image of a Cys(Zn) microsphere. (**v**) Enlarged TEM image of the edge of a Cys(Zn) microsphere. (**vi**) High-resolution TEM image and SAED pattern (inset) of the nanorods [140]. (**b**) Schematic representation of the various types of SCCs and the scope of their biological applications. [46] Adapted with permission from John Wiley and Sons [139] and the American Chemical Society [46]. On the other hand, MOFs represent a specific category of CPs, characterized by their three-dimensional (3D) structures that frequently display considerable porosity with tunable pore sizes [141]. These properties make MOFs ideal for applications like catalysis, where the increased surface area supports active catalytic substances, while the adjustable pores can selectively filter molecules for specific reactions. Furthermore, MOFs serve as effective delivery systems for a variety of therapeutic agents, including drugs, nucleic acids, proteins, and dyes. Their large surface area, tunable pore sizes, and biocompatibility allow for the efficient encapsulation of these cargos, making them highly versatile in biomedical applications. A detailed review by [PERSON] and [PERSON] provides an in-depth analysis of MOFs and their wide-ranging applications in the biomedical field, offering valuable insights into their synthesis, functionalization, and use in areas like drug delivery, bioimaging, and cancer therapy [142]. In theory, the length of organic linkers scales with the pore size of MOFs within a given network. Recently, the concept of supramolecular templating has emerged as an alternative approach for creating hierarchically ordered MOFs. These templates can be classified as hard, such as polystyrene, or soft, including micelles, surfactants, block co-oligomers, and others [143]. In both compounds, coordination chemistry serves as the foundation for both CPs and MOFs, where metal ions interact with organic ligands to create extended structures via coordination bonds [144; 145; 146]. Supramolecular Coordination Complexes (SCCs) Including Two-Dimensional (2D) Metallacycles and Three-Dimensional (3D) Metallacages  
SCCs, on the other hand, are discrete molecular entities formed through the coordination-driven self-assembly of suitable metal centers and ligands containing multiple binding sites [147; 46]. The combination of SCCs and polymers has resulted in hybrid materials with highly diverse and well-defined topological architectures, offering a platform for exploring their potential in various fields.