Inorganic Macrocycle Chemistry and Coordination Complexes

Inorganic macrocycles are large ring-shaped molecules composed predominantly of non-carbon elements, often incorporating group 14 and group 15 atoms, that can bind metal ions and small guests within their cavities. These structures combine the inherent stability of inorganic frameworks with the design flexibility of organic macrocycles, offering unique platforms for catalysis, molecular recognition and materials science. Coordination complexes formed with such macrocycles exploit the directional bonding of metal centres to impose precise geometries, tuning electronic, magnetic and photophysical properties. Recent advances have focused on controlling ring size and topology through modular building‐block strategies, unlocking high-order cyclic architectures that rival organic crown-ethers in cavity dimensions. Parallel efforts in hybrid organic–inorganic systems have demonstrated that pre-arranged ligand motifs can direct the formation of unfolded macrocycles, expanding the toolkit for host–guest chemistry. Together, these developments have elevated inorganic macrocycle chemistry towards applications in ion transport, selective catalysis and the construction of responsive supramolecular assemblies.

Research from Nature Portfolio

Building on modular synthesis, researchers have implemented a “3 + n” cyclisation method to assemble oxygen-bridged phosphazane rings with precise control over macrocycle size. This approach isolated a hexameric cyclodiphosphazane macrocycle whose cavity rivals that of traditional organic crown-ethers, opening pathways for tailored ion encapsulation and selective transport. In a complementary study, a two-step route combining pre-arranged building blocks enabled access to a large unfolded tetrameric cyclodiphosphazane macrocycle not achievable by conventional means. The open-face architecture presents an expanded binding surface and theoretical host–guest simulations suggest promise for proto-rotaxane construction. Together, these contributions demonstrate that increasing building-block complexity and pre-organisation can reliably yield inorganic macrocycles with bespoke cavity shapes and functions.

Inorganic Macrocycle Chemistry and Coordination Complexes publication trend

The graph below shows the total number of articles in inorganic macrocycle chemistry and coordination complexes across all publications each year (not limited to Nature Index journals).

Technical terms

Inorganic macrocycle: A large cyclic molecule composed mainly of non-carbon elements that can encapsulate guests or bind metal ions.

Cyclodiphosphazane: A inorganic ring system containing alternating phosphorus and nitrogen atoms, capable of bridging via oxygen or organic linkers.

Coordination complex: A structure consisting of a central metal ion bonded to surrounding ligands in a defined geometry.

Supramolecular chemistry: The study of non-covalent interactions between molecules that lead to organized assemblies.

Host–guest chemistry: The binding and recognition of a guest molecule or ion within the cavity of a host macrocycle.

References

1. Size-control in the synthesis of oxo-bridged phosphazane macrocycles via a modular addition approach. Communications Chemistry (2021).
2. Steric C–N bond activation on the dimeric macrocycle [{P(μ-NR)} 2 (μ-NR)] 2. Chemical Communications (2015).
3. Pre-arranged building block approach for the orthogonal synthesis of an unfolded tetrameric organic–inorganic phosphazane macrocycle. Communications Chemistry (2022).