Metal-Coordinated Polymer-Inorganic Hybrids: Synthesis, Properties, and Application

Abstract

This review examines the recent advancements and unique properties of polymer-inorganic hybrid materials formed through coordination bonding (Class II hybrids), which enable enhanced functionality and stability across various applications. Here, we categorize these materials based on properties gained through complexation, focusing on electrical conductivity, thermal stability, photophysical characteristics, catalytic activity, and nanoscale self-assembly. Two major synthetic approaches to making these hybrids include homogeneous and heterogeneous methods, each with distinct tradeoffs: Homogeneous synthesis is straightforward but requires favorable mixing between inorganic and polymer species, which are predominantly water-soluble complexes. In contrast, heterogeneous methods are post-processing techniques that provide high area selectivity for inorganic precursors, allowing precise integration within polymer matrices. Finally, we highlight the role of hybrid linkers, namely metallosupramolecular polymers, in creating structural diversity. These can be organized into three main groups: metal-organic frameworks (MOFs), coordination polymers (CPs), and supramolecular coordination complexes (SCCs). Each of these groups introduces unique structural and functional properties that expand the potential applications of hybrid materials.

Keywords: Metal-Coordinated Polymers; Polymer-Inorganic Hybrids; Synthesis Approaches; block copolymers; coordination bonding; metallosupramolecular polymers.

Figure 3

(a) Schematic of atomic layer deposition (ALD) and sequential infiltration synthesis (SIS) processes. ALD provides conformal surface coatings layer by layer, while SIS enables in-depth infiltration of precursors into polymer matrices [65]. (b) Schematic of vapor phase infiltration (VPI) process [68]. (c) Illustration of block copolymer (BCP) templating using annealing techniques as a pre-processing step for vapor phase infiltration (VPI). The self-assembled BCP thin film is annealed to achieve ordered domain structures, which serve as templates for selective infiltration and subsequent material synthesis [79]. (d) Schematics of liquid phase infiltration of BCPs: PS-b-P2VP cylinders are immersed in an acidic metal salt solution, where anionic metal complexes bind to protonated P2VP. O₂ plasma then removes the polymer, reducing metal salts to nanostructures, replicating the BCP morphology [83]. Adapted with permission from the Royal Society of Chemistry [65,68] and American Chemical Society [79].

Figure 8

(a) (i,ii) SEM images of TiO₂ nanowires with a random alignment templated from self-assembled PS-b-PMMA BCP film on a QCM crystal after 8 SIS cycles at 135 °C [125]. (b) (i,ii) Top-view and cross-sectional SEM images of as-infiltrated self-assembled PS-b-P2VP BCP thin films after Pt LPI for 75 s at 22 and 62 °C, respectively. (iii,iv) After oxygen-plasma ashing of the polymer matrix from the Pt-infiltrated PS-b-P2VP BCP thin films in (i,iii). All scale bars denote 100 nm [34]. (c) TEM images and the corresponding schematic illustrations (upper-right insets) of the PS_9.8k-b-P4VP_10k-Pb(II) particles obtained by solvent evaporation of emulsions containing PS_9.8k-b-P4VP_10k in a chloroform phase (10 mg/mL) and Pb(II) ions with varied concentrations, (i) 0 M and (ii) 0.04 M, in PVA aqueous solution (3 mg/mL) [128]. (d) TEM images of the PS_9.8k-b-P4VP_10k-Fe(III) assemblies obtained by solvent evaporation of emulsions containing PS_9.8k-b-P4VP_10k in the chloroform phase (10 mg/mL) and Fe(III) with varied concentrations, (i) 0.001 M and (ii) 0.1 M, in PVA aqueous solution (3 mg/mL) [128]. Adapted with permission from the American Chemical Society [34,125,128].

Figure 1

Synthetic approaches for the MSPs. (A) Post-assembly polymerization approach: metallacycles or metallacages are first formed via coordination-driven self-assembly, followed by polymerization of chains from the core. (B) Post-polymerization assembly approach: pre-synthesized macroligands with polymer chains and coordination sites undergo coordination-driven self-assembly to form MSPs. Red represents the metal ion, green represents the organic linker and blue represents the polymer. Adapted with permission from the Royal Society of Chemistry [52].

Figure 2

Synthetic approaches for the MPNs. (A) Post-assembly polymerization approach: metallacycles or metallacages with multiple reactive sites are first formed through coordination-driven self-assembly. These structures then undergo crosslinking at their reactive sites to create polymer networks with metallacycles/metallacages acting as crosslinking nodes. (B) Post-polymerization assembly approach: polymer chains with coordination sites are synthesized first, followed by coordination-driven self-assembly to form crosslinked MPNs. Red represents the metal ion, green represents the organic linker and blue represents the polymer. Adapted with permission from the Royal Society of Chemistry [52].

Figure 4

(a) Possible tetrahedral coordination complexation of ZnCl₂ with P4VP [102]. (b) A ruthenium bridge between pyridine ligands on two different polymer chains illustrates the concept of coordination crosslinking [96]. (c) Schematic representation of P4VP–metal complexes: sulfate anions coordinated with Cu(II) in monocoordinated and bridged forms. (d) Thiocyanate coordinating through nitrogen, showing structural stabilization within the polymer matrix [93]. (e) Preparation of the PVP–DVB–Cu(II) complex [103]. Adapted with permission from Elsevier [93,96,103].

Figure 5

(a) An illustration of cobalt phthalocyanine (CoPc) encapsulated within a hydrophobic poly-4-vinylpyridine (P4VP) membrane highlighting the postulated primary-, secondary-, and outer-coordination sphere effects [109]. (b) Schematic synthesis of a P4VP–Ru polymer–metal complex by a combination of RAFT polymerization and a pyridine/DMSO exchange reaction [110]. (c) Proposed structure of Ru-PVP/CNT [111]. (d) Proposed Cu(II) structures in the fresh catalysts [112]. (e) Left: structure of the redox polymer osmium bipyridine PVP. Right: schematic cross section of the glucose-sensitive ^EMOSFET [113]. Adapted with permission from the Royal Society of Chemistry [111,113] and Elsevier [112].

Figure 6

(a) Preparation of P4VP-Au (I) polymer complex: the synthesis involves the coordination of poly(4-vinylpyridine) (P4VP) with (Me₂S)AuCl in a mixture of ethanol (EtOH) and dichloromethane (DCM) at room temperature [99]. (b) Suggested structural model showing intrachain and interchain aurophilic interactions in metallopolymers 1 and 2 [114]. Adapted with permission from the American Chemical Society [114].

Figure 7

(a) Schematic representation of [Cu(phen)(L−tyr)BPEI]ClO₄. (b) Morphological analysis of MCF−7 cancer cells stained with acridine orange and ethidium bromide after treatment with [Cu(phen)(L−tyr)BPEI]ClO₄. The images show a time−dependent increase in apoptosis, indicated by chromatin condensation and cell shrinkage. Scale bar: 35 µm [120]. (c) Schematic illustration for fabrication of PEI/Au NPs for colorimetric detection of Cu²⁺ [121]. Adapted with permission from Elsevier [120,121].

Figure 9

(a) Synthesis of the first polymers with pendant [Ru(bpy)₃] complexes. This complex is synthesized via radical polymerization of a polystyrene backbone, followed by bromination, lithiation, and functionalization with 2,2′-bipyridine. (b) Left: preparation of star-shaped polymers by the addition of metal ions to monofunctionalized bipyridine polymers; right: GPC analysis showed a significant shift in the molecular weight after complexation. Adapted with permission from John Wiley and Sons [135].

Figure 10

(a) (i) SEM image of Cys(Zn) microspheres obtained from the assembly of cystine (2 mm) and ZnCl₂ (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].